FLEX-NUCLEOSIDE ANALOGUES, NOVEL THERAPEUTICS AGAINST VIRUSES CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application claims priority to U.S. Provisional Patent Application No.63/351,843 filed on June 14, 2022 in the name of Katherine L. Radtke and entitled “Design, synthesis and methods of use of fleximer nucleoside analogues having anti-virus activity,” U.S. Provisional Patent Application No. 63/391,344 filed on July 22, 2022 in the name of Katherine L. Radtke and entitled “Design, synthesis and methods of use of fleximer nucleoside analogues having anti-viral activity against hepatitis B virus (HBV),” and U.S. Provisional Patent Application No. 63/377,360 filed on September 28, 2022 in the name of Katherine L. Radtke and entitled “Flex-nucleoside analogues, novel therapeutics against coronaviruses, herpesviruses, alphaviruses, polyomaviruses, enteroviruses, filoviruses, matonaviruses, phenuiviruses, and flaviviruses,” which are all hereby incorporated by reference herein in their entirety. FIELD [0002] The present invention is directed to nucleoside analogue compounds, compositions comprising same, and methods for treating or preventing any one of coronaviruses, herpesviruses, alphaviruses, enteroviruses, polyomaviruses, filoviruses, matonaviruses, phenuiviruses, Hepatitis B virus, and/or flaviviruses using said nucleosides analogues. Specifically, the present invention provides for the design and synthesis of fleximer and reverse fleximer nucleoside analogues having increased flexibility and ability to alter their conformation to provide increased antiviral activity potential that can inhibit several viruses. BACKGROUND [0003] Viruses are small infectious agents that can only multiply within the cells of animals, plants, and bacteria. The structures of viruses are simple compared to living cells and contain a small haploid DNA or RNA genome and a protein or glycoprotein coat called a capsid. In addition, some viruses called enveloped viruses are surrounded by a lipid membrane. [0004] A number of viruses appear on the United States National Institutes of Allergy and Infectious Disease (NIAID) list of Emerging Diseases/Pathogens list, which include Coronaviruses (e.g., SARS- 1, SARS-2, Middle East respiratory syndrome (MERS), COVID-19, and mutants thereof), Flaviviruses (e.g., Dengue, Zika, yellow fever, tickborne encephalitis, HCV, and West Nile), Herpesviruses (e.g., herpes simplex virus 1, herpes simplex virus 2, varicella-zoster virus, Epstein-Barr virus, cytomegalovirus, Human herpesvirus-6, Human herpesvirus-7, and Kaposi’s sarcoma herpes virus), alphavirus (e.g., eastern equine encephalomyelitis (EEE), Venezuelan equine encephalomyelitis (VEE) and western equine encephalomyelitis (WEE)), enteroviruses (e.g., echovirus and coxsackievirus), Filoviruses (e.g., Ebola virus, Sudan virus, and Marburg virus), matonaviruses (e.g., Rubella, Rustrela, and Ruhugu), and phenuiviruses (e.g., Rift Valley Fever virus) to name a few. [0005] Filoviruses are enveloped viruses with a genome consisting of one linear single-stranded RNA segment of negative polarity. The viral genome encodes 7 proteins. Nucleoprotein (NP), virion protein 35 kDa (VP35) and virion protein 30 kDa (VP30) are associated with the viral ribonucleoprotein complex. Members of the filovirus genus include Zaire Ebola virus, Sudan Ebola virus, Reston Ebola virus, Cote d'Ivoire Ebola virus and Marburg virus. Ebola and Marburg viruses can cause severe hemorrhagic fever and have a high mortality rate. Ebola virus (Zaire and Sudan species) was first described in 1976 after outbreaks of a febrile, rapidly fatal hemorrhagic illness were reported along the Ebola River in Zaire (now the Democratic Republic of the Congo) and Sudan. The natural host for Ebola viruses is still unknown but is widely speculated to be bats. Marburg virus, named after the German town where it was first reported in 1967, is primarily found in equatorial Africa. The host range of Marburg virus includes non-human and human primates. [0006] Viruses in the genus flavivirus are known to cause viral hemorrhagic fevers (VHFs). Flaviviruses are enveloped viruses with a genome consisting of one linear single-stranded RNA segment of positive polarity. The polyprotein is co- and post-transcriptionally cleaved by cell signal peptidase and the viral protease to generate individual viral proteins. Viral structural proteins include capsid (C), precursor to M (prM), minor envelope (M) and major envelope (E). Members of the flavivirus genus include yellow fever virus, Apoi virus, Aroa virus, Bagaza virus, Banzi virus, Bouboui virus, Bukalasa bat virus, Cacipacore virus, Carey Island virus, Cowbone Ridge virus, Dakar bat virus, dengue virus, Edge Hill virus, Entebbe bat virus, Gadgets Gully virus, Ilheus virus, Israel turkey meningoencephalomyelitis virus, Japanese encephalitis virus, Jugra virus, Jutiapa virus, Kadam virus, Kedougou virus, Kokobera virus, Koutango virus, Kyasanur Forest disease virus, Langat virus, Louping ill virus, Meaban virus, Modoc virus, Montana myotis leukoencephalitis virus, Murray Valley encephalitis virus, Ntaya virus, Omsk hemorrhagic fever virus, Phnom Phenh bat virus, Powassan virus, Rio Bravo virus, Royal Farm virus, Saboya virus, Sal Vieja virus, San Perlita virus, Saumarez Reef virus, Sepik virus, St. Louis encephalitis virus, Tembusu virus, tick-borne encephalitis virus, Tyuleniy virus, Uganda S virus, Usutu virus, Wesselsbron virus, West Nile virus, Yaounde virus, Yokose virus, Zika virus, cell fusing agent virus and Tamana bat virus. [0007] Coronaviruses are enveloped viruses, having a capsid exhibiting a helical symmetry. They have a single-stranded positive sense RNA genome and are capable of infecting cells from birds and mammals. The viruses, which are members of this very wide family, are known to be causative agents for the common cold (for example, human coronaviruses (HCoV) 229E and OC43), bronchiolitis (for example NL63 virus) or even some forms of pneumoniae, e.g., as those observed during the SARS (such as the Severe Acute Respiratory Syndrome Coronavirus, SARS-CoV) epidemic. In January 2020 the World (COVID-19 disease) which has shown a higher mortality rate than MERS-CoV or SARS-CoV and exhibits an ongoing risk of human-to-human transmission. [0008] Viral hepatitis such as hepatitis B is an important and major disease threatening the life and health of people, and the fundamental approach for treatment of hepatitis B is an antiviral treatment. Although there exists a highly effective HBV vaccine, it is not readily available in some nations (e.g., developing nations). At present, clinically effective drugs against hepatitis B virus are mainly interferons or L-nucleosides (such as Lamivudine), which are preferred because they are significantly less toxic compared to D-nucleosides. However, the effective rate of interferon treatment is just 30- 50% and has dose-dependent toxicity and side-effects. Lamivudine has pronounced activity against hepatitis B virus but may result in drug resistance during long-term administration, which is likely since treatment for chronic HBV is life-long. With the increased interest toward effective treatment of HBV, other L-nucleosides were developed such as Emtricitabine, telbivudine (L-dT), 1-(2-deoxy-2-fluoro-β- L-arabinofuranosyl)-5-methyluracil (Clevudine, L-FMAU), and Elvucitabine, or L-d4FC. [0009] There are relatively few prophylactic or therapeutic agents for treatment of viral diseases caused by Coronaviruses, Alphaviruses, Enteroviruses, Herpesviruses, Flaviviruses, Matonaviridae, Phenuiviridae, Hepatitis B virus, and/or Filoviruses. The need for new and more effective antiviral therapeutics, particularly those targeting emerging and reemerging infectious diseases and pathogens continues to increase. Thus, in light of the above discussion, there is a need for discovering and providing new and more efficient antiviral drugs. SUMMARY [0010] The present invention provides for flexible and modified nucleoside analogues that allow access to more potential binding sites with the ability to retain their potency against viral diseases caused by a virus including, but not limited to, Coronaviruses, Polyomaviruses, Herpesviruses, Alphaviruses, Enteroviruses, Flaviviruses, Matonaviruses, Phenuiviruses, Hepatitis B virus, and Filoviruses, since the flexible and modified nucleoside analogues of the present invention can "wiggle and jiggle" in the binding site. These findings are causing a paradigm shift in drug design having antiviral activity. [0011] In one aspect, a flexible nucleoside analogue is described, said flexible nucleoside analogue selected from at least one of: (i) at least one compound comprising a Flex-Cidofovir scaffold selected from:

, wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X ₁ , X ₂ , X ₃ , and X ₄ are each independently selected from C, O, N, or S; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, NH- OH, alkyl, CF ₃ , Cl, CN, or N ₃ ; Y ₃ is H, alkyl, NH ₂ , OH, O-alkyl, or NH-alkyl; W ₁ and W ₂ are each independently selected from H, alkyl, F, Cl, Br, I, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, COOH, CONH ₂ , or NHNH ₂ ; Z1, Z2, and Z3 are each independently selected from C or a heteroatom; and R ₁ is phosphonate, monophosphate phosphonate, and diphosphate phosphonate, or various prodrugs (e.g., esters, McGuigan ProTides, diisoproxyl fumarate, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); (ii) at least one compound comprising a Flex-BCNA scaffold selected from: , wherein R ₁ is H, NH ₂ , OH, O-alkyl, NH-alkyl, or F; R ₂ is H, NH ₂ , OH, NHOH, O-alkyl, or NH-alkyl; R i H OH F Cl CH th l d R ₄ is H, F, Cl, OH, CH ₃ , ethynyl, or prodrug ; R ₅ is H, monophosphate, diphosphate, triphosphate, various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); R ₆ is H, NH ₂ , OH, alkyl, F, Br, Cl, I, CN, CF ₃ , NO ₂ , O-alkyl, NH-alkyl, CO ₂ H, CONH ₂ , NHNH ₂ , esters or prodrugs; Z ₁ , Z ₂ , Z ₃ , Z ₄ , Z ₅ , and Z ₆ are each independently selected from C or N; and Y is null, CH ₂ , NH, O, vinyl, -NH(CH ₂ ) _n -, -O(CH ₂ ) _n -, ethynyl, wherein n = 1-4; (iii) at least one reverse fleximer D-nucleoside selected from: , wherein X ₁ ,X _{2 ,} X ₃ ,and X ₄ are each independently selected from C, O, N, or S; X ₅ is O, NH, S, or CH ₂ ; W ₁ and W ₂ are each independently selected from H, Cl, Br, I, F _, alkyl, CF ₃ , NH ₂ , OH, O- alkyl, NH-alkyl, cyano, amide, NO ₂ , CO ₂ H, CONH ₂ , NHNH ₂ , esters or prodrugs; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, alkyl, CF ₃ , N ₃ , Cl, or CN; Y ₃ is H, alkyl, NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g., amino acid prodrugs); R ₃ is H, OH, N ₃ , or various prodrugs (e.g., amino acid prodrugs); R ₄ is H, F, ethynyl, or cyano; L is null, NH, CH ₂ , O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; and R ₅ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, M

, wherein X ₁ , X ₂ , X ₃ and X ₄ are each independently selected from C, O, N, or S; X ₅ is O, NH, S, or CH ₂ ; W ₁ and W ₂ are each independently selected from H, F, Cl, Br, I, alkyl, CF ₃ , NH ₂ , OH, O- alkyl, NH-alkyl, cyano, amide, CO ₂ H, CONH ₂ , NHNH ₂ , NO ₂ , esters or prodrugs; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, alkyl, CF ₃ , N ₃ , Cl, or CN; Y ₃ is H, CH ₃ , NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g., amino acid prodrugs); R ₃ is H, F, ethynyl, or cyano; L is null, NH, CH ₂ , O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; and R ₄ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); (iv) at least one proximal reverse fleximer L-nucleoside selected from:

, wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X1, X2, X3, and X4 are each independently selected from C, O, N, or S; X ₅ is O, NH, S, or CH ₂ ; W ₁ and W ₂ are each independently selected from H, F, Cl, Br, I, alkyl, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, amide, CO ₂ H, CONH ₂ , NHNH ₂ , NO ₂ , esters or prodrugs; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, NH- OH, alkyl, CF ₃ , Cl, CN, or N ₃ ; Y ₃ is H, alkyl, NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g., amino acid prodrugs); R ₃ is H, OH, N ₃ , or various prodrugs (e.g., amino acid prodrugs); R ₄ is H, F, methyl, ethynyl, azido or cyano; and R ₅ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); or , wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X ₁ , X ₂ , X ₃ , and X ₄ are each independently selected from C, O, N, or S; X ₅ is CH ₂ , O, NH, or S; W ₁ and W ₂ are each independently selected from H, F, Br, Cl, I, alkyl, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, amide, NO ₂ , CO ₂ H, CONH ₂ , or NHNH ₂ ; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, NH- OH, alkyl, CF ₃ , Cl, CN, or N ₃ ; Y ₃ is H, alkyl, NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g., amino acid prodrugs); R ₃ is H, F, ethynyl or cyano; and R ₄ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); and (v) at least one distal reverse fleximer L-nucleoside selected from: wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X ₁ , X ₂ , X ₃ , and X ₄ are each independently selected from C, O, N, or S; X ₅ is O, NH, S, or CH ₂ ; W ₁ and W ₂ are each independently selected from H, F, Cl, Br, I, alkyl, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, COOH, CONH2, or NHNH2; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, or NH- OH, alkyl, CF ₃ , N ₃ , Cl, CN; Y ₃ is H, alkyl, NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl _, alkyl, ethynyl, or various prodrugs (e.g. amino acid prodrugs); R ₃ is H, OH, N ₃ , or various prodrugs (e.g., amino acid prodrugs); R ₄ is H, F, ethynyl or cyano; and R ₅ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); or wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X ₁ , X ₂ , X ₃ , and X ₄ are each independently selected from C, O, N, or S; X ₅ is CH ₂ , O, NH, or S; W ₁ and W ₂ are each independently selected from H, F, Br, Cl, I, alkyl, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, amide, NO ₂ , CO ₂ H, CONH ₂ , or NHNH ₂ ; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, NH- OH, alkyl, CF ₃ , Cl, CN, or N ₃ ; Y ₃ is H, CH ₃ , NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g. amino acid prodrugs); R ₃ is H, F, ethynyl or cyano; and R ₄ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs), or a pharmaceutically acceptable salt, isomer, hydrate, prodrug or solvate thereof. [0012] In another aspect, a pharmaceutical composition comprising at least one of the flexible nucleoside analogue and at least one pharmaceutically acceptable carrier is disclosed, wherein the at least one flexible nucleoside analogue is selected from at least one of: (i) at least one compound comprising a Flex-Cidofovir scaffold selected from: , wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X1, X2, X3, and X4 are each independently selected from C, O, N, or S; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, NH- OH, alkyl, CF ₃ , Cl, CN, or N ₃ ; Y ₃ is H, alkyl, NH ₂ , OH, O-alkyl, or NH-alkyl; W ₁ and W ₂ are each independently selected from H, alkyl, F, Cl, Br, I, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, COOH, CONH ₂ , or NHNH ₂ ; Z ₁ , Z ₂ , and Z ₃ are each independently selected from C or a heteroatom; and R ₁ is phosphonate, monophosphate phosphonate, and diphosphate phosphonate, or various prodrugs (e.g., esters, McGuigan ProTides, diisoproxyl fumarate, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); (ii) at least one compound comprising a Flex-BCNA scaffold selected from: , wherein R ₁ is H, NH ₂ , OH, O-alkyl, NH-alkyl, or F; R ₂ is H, NH ₂ , OH, NHOH, O-alkyl, or NH-alkyl; R ₃ is H, OH, F, Cl, CH ₃ , ethynyl, or prodrug; R ₄ is H, F, Cl, OH, CH ₃ , ethynyl, or prodrug ; R ₅ is H, monophosphate, diphosphate, triphosphate, various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); R ₆ is H, NH ₂ , OH, alkyl, F, Br, Cl, I, CN, CF ₃ , NO ₂ , O-alkyl, NH-alkyl, CO ₂ H, CONH ₂ , NHNH ₂ , esters or prodrugs; Z ₁ , Z ₂ , Z ₃ , Z ₄ , Z ₅ , and Z ₆ are each independently selected from C or N; and Y is null, CH ₂ , NH, O, vinyl, -NH(CH ₂ ) _n -, -O(CH ₂ ) _n -, ethynyl, wherein n = 1-4; (iii) at least one reverse fleximer D-nucleoside selected from: , wherein X ₁ ,X _{2 ,} X ₃ ,and X ₄ are each independently selected from C, O, N, or S; X ₅ is O, NH, S, or CH ₂ ; W ₁ and W ₂ are each independently selected from H, Cl, Br, I, F _, alkyl, CF ₃ , NH ₂ , OH, O- alkyl, NH-alkyl, cyano, amide, NO ₂ , CO ₂ H, CONH ₂ , NHNH ₂ , esters or prodrugs; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, alkyl, CF ₃ , N ₃ , Cl, or CN; Y ₃ is H, alkyl, NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g., amino acid prodrugs); R ₃ is H, OH, N ₃ , or various prodrugs (e.g., amino acid prodrugs); R ₄ is H, F, ethynyl, or cyano; L is null, NH, CH ₂ , O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; and R ₅ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); or , wherein X ₁ , X ₂ , X ₃ and X ₄ are each independently selected from C, O, N, or S; X ₅ is O, NH, S, or CH ₂ ; W ₁ and W ₂ are each independently selected from H, F, Cl, Br, I, alkyl, CF ₃ , NH ₂ , OH, O- alkyl, NH-alkyl, cyano, amide, CO ₂ H, CONH ₂ , NHNH ₂ , NO ₂ , esters or prodrugs; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, alkyl, CF ₃ , N ₃ , Cl, or CN; Y ₃ is H, CH ₃ , NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g., amino acid prodrugs); R ₃ is H, F, ethynyl, or cyano; L is null, NH, CH ₂ , O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; and R ₄ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); (iv) at least one proximal reverse fleximer L-nucleoside selected from: , wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X ₁ , X ₂ , X ₃ , and X ₄ are each independently selected from C, O, N, or S; X ₅ is O, NH, S, or CH ₂ ; W ₁ and W ₂ are each independently selected from H, F, Cl, Br, I, alkyl, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, amide, CO ₂ H, CONH ₂ , NHNH ₂ , NO ₂ , esters or prodrugs; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, NH- OH, alkyl, CF ₃ , Cl, CN, or N ₃ ; Y ₃ is H, alkyl, NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g., amino acid prodrugs); R ₃ is H, OH, N ₃ , or various prodrugs (e.g., amino acid prodrugs); R ₄ is H, F, methyl, ethynyl, azido or cyano; and R ₅ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); or

, wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X ₁ , X ₂ , X ₃ , and X ₄ are each independently selected from C, O, N, or S; X ₅ is CH ₂ , O, NH, or S; W ₁ and W ₂ are each independently selected from H, F, Br, Cl, I, alkyl, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, amide, NO ₂ , CO ₂ H, CONH ₂ , or NHNH ₂ ; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, NH- OH, alkyl, CF ₃ , Cl, CN, or N ₃ ; Y ₃ is H, alkyl, NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g., amino acid prodrugs); R ₃ is H, F, ethynyl or cyano; and R ₄ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); and (v) at least one distal reverse fleximer L-nucleoside selected from:

wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X ₁ , X ₂ , X ₃ , and X ₄ are each independently selected from C, O, N, or S; X ₅ is O, NH, S, or CH ₂ ; W ₁ and W ₂ are each independently selected from H, F, Cl, Br, I, alkyl, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, COOH, CONH ₂ , or NHNH ₂ ; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, or NH- OH, alkyl, CF ₃ , N ₃ , Cl, CN; Y ₃ is H, alkyl, NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl _, alkyl, ethynyl, or various prodrugs (e.g. amino acid prodrugs); R ₃ is H, OH, N ₃ , or various prodrugs (e.g., amino acid prodrugs); R ₄ is H, F, ethynyl or cyano; and R ₅ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); or wherein L i ll CH NH O i l h l O (CH ) NH (CH ) n is any integer from 1-4; X ₁ , X ₂ , X ₃ , and X ₄ are each independently selected from C, O, N, or S; X ₅ is CH ₂ , O, NH, or S; W ₁ and W ₂ are each independently selected from H, F, Br, Cl, I, alkyl, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, amide, NO ₂ , CO ₂ H, CONH ₂ , or NHNH ₂ ; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, NH- OH, alkyl, CF ₃ , Cl, CN, or N ₃ ; Y ₃ is H, CH ₃ , NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g. amino acid prodrugs); R ₃ is H, F, ethynyl or cyano; and R ₄ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs), or a pharmaceutically acceptable salt, isomer, hydrate, prodrug or solvate thereof. [0013] In yet another aspect, a method for treating and/or preventing a viral infection in a subject is disclosed, wherein the viral infection is caused by at least one of a coronavirus, a herpesvirus, an alphavirus, a polyomavirus, an enterovirus, a filovirus, a matonavirus, a phenuivirus, a Hepatitis B virus, and/or a flavivirus, comprising administration, to the subject, of a therapeutically effective amount of at least one fleximer nucleoside analogue, or a pharmaceutical composition comprising same, wherein the at least one fleximer nucleoside analogue is selected from at least one of: (i) at least one compound comprising a Flex-Cidofovir scaffold selected from: , wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X ₁ , X ₂ , X ₃ , and X ₄ are each independently selected from C, O, N, or S; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, NH- OH, alkyl, CF ₃ , Cl, CN, or N ₃ ; Y ₃ is H, alkyl, NH ₂ , OH, O-alkyl, or NH-alkyl; W ₁ and W ₂ are each independently selected from H, alkyl, F, Cl, Br, I, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, COOH, CONH ₂ , or NHNH ₂ ; Z ₁ , Z ₂ , and Z ₃ are each independently selected from C or a heteroatom; and R ₁ is phosphonate, monophosphate phosphonate, and diphosphate phosphonate, or various prodrugs (e.g., esters, McGuigan ProTides, diisoproxyl fumarate, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); (ii) at least one compound comprising a Flex-BCNA scaffold selected from: , wherein R ₁ is H, NH ₂ , OH, O-alkyl, NH-alkyl, or F; R ₂ is H, NH ₂ , OH, NHOH, O-alkyl, or NH-alkyl; R ₃ is H, OH, F, Cl, CH ₃ , ethynyl, or prodrug; R ₄ is H, F, Cl, OH, CH ₃ , ethynyl, or prodrug ; R ₅ is H, monophosphate, diphosphate, triphosphate, various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); R ₆ is H, NH ₂ , OH, alkyl, F, Br, Cl, I, CN, CF ₃ , NO ₂ , O-alkyl, NH-alkyl, CO ₂ H, CONH ₂ , NHNH ₂ , esters or prodrugs; Z ₁ , Z ₂ , Z ₃ , Z ₄ , Z ₅ , and Z ₆ are each independently selected from C or N; and Y is null, CH ₂ , NH, O, vinyl, -NH(CH ₂ ) _n -, -O(CH ₂ ) _n -, ethynyl, wherein n = 1-4; (iii) at least one reverse fleximer D-nucleoside selected from:

, wherein X ₁ ,X _{2 ,} X ₃ ,and X ₄ are each independently selected from C, O, N, or S; X ₅ is O, NH, S, or CH ₂ ; W ₁ and W ₂ are each independently selected from H, Cl, Br, I, F _, alkyl, CF ₃ , NH ₂ , OH, O- alkyl, NH-alkyl, cyano, amide, NO ₂ , CO ₂ H, CONH ₂ , NHNH ₂ , esters or prodrugs; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, alkyl, CF ₃ , N ₃ , Cl, or CN; Y ₃ is H, alkyl, NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g., amino acid prodrugs); R ₃ is H, OH, N ₃ , or various prodrugs (e.g., amino acid prodrugs); R ₄ is H, F, ethynyl, or cyano; L is null, NH, CH ₂ , O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; and R ₅ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); or , wherein X ₁ , X ₂ , X ₃ and X ₄ are each independently selected from C, O, N, or S; X ₅ is O, NH, S, or CH ₂ ; W ₁ and W ₂ are each independently selected from H, F, Cl, Br, I, alkyl, CF ₃ , NH ₂ , OH, O- alkyl, NH-alkyl, cyano, amide, CO ₂ H, CONH ₂ , NHNH ₂ , NO ₂ , esters or prodrugs; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, alkyl, CF ₃ , N ₃ , Cl, or CN; Y ₃ is H, CH ₃ , NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g., amino acid prodrugs); R ₃ is H, F, ethynyl, or cyano; L is null, NH, CH ₂ , O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; and R ₄ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); (iv) at least one proximal reverse fleximer L-nucleoside selected from: , wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X ₁ , X ₂ , X ₃ , and X ₄ are each independently selected from C, O, N, or S; X ₅ is O, NH, S, or CH ₂ ; W ₁ and W ₂ are each independently selected from H, F, Cl, Br, I, alkyl, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, amide, CO ₂ H, CONH ₂ , NHNH ₂ , NO ₂ , esters or prodrugs; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, NH- OH, alkyl, CF ₃ , Cl, CN, or N ₃ ; Y ₃ is H, alkyl, NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g., amino acid prodrugs); R ₃ is H, OH, N ₃ , or various prodrugs (e.g., amino acid prodrugs); R ₄ is H, F, methyl, ethynyl, azido or cyano; and R ₅ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); or , wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X ₁ , X ₂ , X ₃ , and X ₄ are each independently selected from C, O, N, or S; X ₅ is CH ₂ , O, NH, or S; W ₁ and W ₂ are each independently selected from H, F, Br, Cl, I, alkyl, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, amide, NO ₂ , CO ₂ H, CONH ₂ , or NHNH ₂ ; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, NH- OH, alkyl, CF ₃ , Cl, CN, or N ₃ ; Y3 is H, alkyl, NH2, OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g., amino acid prodrugs); R ₃ is H, F, ethynyl or cyano; and R ₄ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); and (v) at least one distal reverse fleximer L-nucleoside selected from: wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X ₁ , X ₂ , X ₃ , and X ₄ are each independently selected from C, O, N, or S; X ₅ is O, NH, S, or CH ₂ ; W1 and W2 are each independently selected from H, F, Cl, Br, I, alkyl, CF3, NH2, OH, O-alkyl, NH-alkyl, cyano, COOH, CONH ₂ , or NHNH ₂ ; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, or NH- OH, alkyl, CF ₃ , N ₃ , Cl, CN; Y ₃ is H, alkyl, NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl _, alkyl, ethynyl, or various prodrugs (e.g. amino acid prodrugs); R ₃ is H, OH, N ₃ , or various prodrugs (e.g., amino acid prodrugs); R ₄ is H, F, ethynyl or cyano; and R ₅ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); or

wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X ₁ , X ₂ , X ₃ , and X ₄ are each independently selected from C, O, N, or S; X ₅ is CH ₂ , O, NH, or S; W ₁ and W ₂ are each independently selected from H, F, Br, Cl, I, alkyl, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, amide, NO ₂ , CO ₂ H, CONH ₂ , or NHNH ₂ ; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, NH- OH, alkyl, CF ₃ , Cl, CN, or N ₃ ; Y ₃ is H, CH ₃ , NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g. amino acid prodrugs); R ₃ is H, F, ethynyl or cyano; and R ₄ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs), or a pharmaceutically acceptable salt, isomer, hydrate, prodrug or solvate thereof. [0014] Other aspects, features and embodiments of the invention will be more fully apparent from the ensuing disclosure and appended claims. BRIEF DESCRIPTION OF THE FIGURES [0015] Figure 1. Proposed synthesis of CHK-01, CHK-02, CHK-03, CHK-04, CHK-05, CHK-06, CHK-07, and CHK-08. DETAILED DESCRIPTION [0016] Although the claimed subject matter will be described in terms of certain embodiments, other embodiments, including embodiments that do not provide all of the benefits and features set forth herein, are within the scope of this disclosure as well. Various structural and parameter changes may be made without departing from the scope of this disclosure. [0017] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict, the present document, including definitions, will control. Preferred methods and materials are described below, although methods and materials similar or equivalent to those described herein can be used in practice or testing of the present disclosure. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. The materials, methods, and examples disclosed herein are illustrative only and not intended to be limiting. [0018] “About” and “approximately” are used to provide flexibility to a numerical range endpoint by providing that a given value may be “slightly above” or “slightly below” the endpoint without affecting the desired result, for example, +/- 5%. [0019] The phrase “in one embodiment” or “in some embodiments” as used herein does not necessarily refer to the same embodiment, though it may. Furthermore, the phrase “in another embodiment” as used herein does not necessarily refer to a different embodiment, although it may. Thus, as described below, various embodiments of the invention may be readily combined, without departing from the scope or spirit of the invention. [0020] The terms “comprise(s),” “include(s),” “having,” “has,” “can,” “contain(s),” and variants thereof, as used herein, are intended to be open-ended transitional phrases, terms, or words that do not preclude the possibility of additional acts or structures. The singular forms “a,” “and” and “the” include plural references unless the context clearly dictates otherwise. The present disclosure also contemplates other embodiments “comprising,” “consisting of” and “consisting essentially of,” the embodiments or elements presented herein, whether explicitly set forth or not. [0021] As defined herein, “alkyl” group corresponds to a C ₁ -C ₆ straight or branched-chain group, having the general formula of C _n H _2n+1 including, but not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, t-butyl, n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1- ethylpropyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, n-hexyl, 4-methylpentyl, 3- methylpentyl, 2-methylpentyl, 1-methylpentyl, 1,3-dimethylbutyl, 1,2-dimethylbutyl, 3,3- dimethylbutyl, 1-methyl-2,2-dimethylpropyl, 1-ethylbutyl, 1-ethyl-2-methylpropyl, and 2-ethylbutyl. In addition, an alkyl group includes a C ₃ -C ₆ cycloalkyl group having the general formula of C _n H _2n−1 including, but not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclopentenyl, and cyclohexyl. [0022] As defined herein, a “halide” corresponds to fluoride, chloride, bromide or iodide. [0023] As defined herein, an “aryl” group corresponds to a functional group derived from an aromatic ring (e.g., an aromatic hydrocarbon ring) by the removal of one hydrogen atom. [0024] As defined herein, a “heteroatom” includes nitrogen, oxygen, sulfur, and silicon. In some embodiments, the heteroatom is nitrogen. [0025] “Subject” as used herein refers to any vertebrate such as mammals, birds, reptiles, amphibians and fish including, but not limited to, a bear, cow, cattle, pig, camel, llama, horse, goat, rabbit, sheep, hamster, guinea pig, cat, tiger, lion, cheetah, jaguar, bobcat, mountain lion, dog, wolf, coyote, rat, mouse, monkey, chimpanzee, and humans. In some embodiments, the subject is a human. [0026] “Treat,” “treating” or “treatment” are each used interchangeably herein to describe reversing, alleviating, or inhibiting the progress of a disease and/or injury, or one or more symptoms of such disease, to which such term applies. Depending on the condition of the subject, the term also refers to preventing a disease, and includes preventing the onset of a disease, or preventing the symptoms associated with a disease. A treatment may be either performed in an acute or chronic way. The term also refers to reducing the severity of a disease or symptoms associated with such disease prior to affliction with the disease. Such prevention or reduction of the severity of a disease prior to affliction refers to administration of a pharmaceutical composition to a subject that is not at the time of administration afflicted with the disease. “Preventing” also refers to preventing the recurrence of a disease or of one or more symptoms associated with such disease. “Treatment” and “therapeutically,” refer to the act of treating, as “treating” is defined above. [0027] As defined herein, “lipid phosphates” include, but are not limited to, [0028] As defined herein, “McGuigan ProTides” correspond to prodrugs of monophosphate nucleotide analogs, including phosphoramidate prodrugs (known as “ProTide” prodrugs). These nucleotide ProTide prodrugs were developed by Prof. McGuigan, for example as described in PCT Applications WO90/05736; WO90/10012; WO9629336; WO2000/047591; WO2001/083501; WO2001085749; WO2003/061670; and WO2005/012327, which are incorporated herein by reference in their entirety. The McGuigan ProTides have been successfully applied to a vast number of nucleoside analogues with antiviral and anticancer activity. ProTides consist of a 5′-nucleoside monophosphate in which the two hydroxyl groups are masked with an amino acid ester and an aryloxy component which once in the cell is enzymatically metabolized to deliver free 5′-monophosphate, which is further transformed to the active 5′-triphosphate form of the nucleoside analogue. In some embodiments, the McGuigan Protide has the structure: , wherein X is a substituted or unsubstituted aryl, naphthalene or biphenyl, wherein the substitutions include, but are not limited to, OH, NH ₂ , F, alkyl, O-alkyl, and/or NH-alkyl; Z is the side chain of the amino acid including, but not limited to, methyl (i.e., the amino acid is alanine), and isopropyl (i.e., the amino acid is valine); ^{Y is O or CH} _{2; and} R is an alkyl or aryl group including, but not limited to, methyl, isopropyl, isobutyl, sec-butyl, or ethyl butyl. [0029] As defined herein, “Tol” is a toluoyl group, having the formula CH ₃ -C ₆ H ₄ -C(=O)-, wherein the methyl group can be ortho-, meta-, or para-. In some embodiments, the methyl group is positioned in the para- position. Flexible nucleoside analogues [0030] Unique nucleoside analogues have been termed “fleximers” and were designed to explore how nucleobase flexibility affects the recognition, binding, and activity of nucleoside(tide) analogues. The fleximers possess a purine base scaffold in which the imidazole (i.e., fleximers) or pyrimidine (i.e., reverse fleximers) moieties are attached by a single carbon–carbon bond, rather than being ‘fused’ as is typical for the purines. These analogues are designed to retain all of the requisite purine hydrogen bonding patterns while allowing the nucleobase to explore alternative binding modes. In some embodiments, fleximers and reverse fleximers allow access to more potential binding sites with the ability to retain their potency against resistant cancers and viral strains since they can "wiggle and jiggle" in the binding site. These findings are causing a paradigm shift in drug design having anticancer and antiviral activity. [0031] The fleximers and reverse fleximers described herein may include several types of modifications: that being parent prox- and distal fleximers connected at 4,5 or 5,6, fleximers connected at 4,6 and 5,5, as well as fleximers and reverse fleximers with a linker positioned between the two heterocyclic base pieces, substituent(s) on the inside of the two heterocyclic pieces to hold the rotation of the flex-base in a particular conformation referred to as T3 analogues ("tune the twist"). Advantageously, the fleximers and reverse fleximers described herein have high bioavailability. [0032] It should be appreciated that any of the fleximer and reverse fleximer nucleoside analogues described herein can be present as tautomers, or interchangeable forms, of the specific molecule described. Tautomers contemplated include the interchange between an enol form and a keto form, between a lactam form and a lactim form, between an amide form and an imidic acid form, and between an amine form and an imine form. [0033] In a first aspect, the present invention broadly relates to fleximer and reverse fleximer nucleoside analogues. In some embodiments of the first aspect, a series of fleximer and reverse fleximer nucleoside analogues are described, wherein the flexible nucleoside analogues are selected from at least one of: (i) at least one compound comprising a Flex-Acyclovir scaffold selected from: R R wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X ₁ and X ₂ are each independently selected from C, O, N, or S; X ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, NH- OH, alkyl, CF ₃ , Cl, CN, or N ₃ ; W ₁ and W ₂ are each independently selected from H, F, alkyl, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, or amide; Z ₁ and Z ₂ are each independently selected from C or a heteroatom; and R ₁ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); (ii) at least one compound comprising a Flex-tenofovir scaffold selected from: , wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X1 and X2 are each independently selected from C, O, N, or S; X ₃ is C or N; W ₁ and W ₂ are each independently selected from H, alkyl, F, Cl, Br, I, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, or amide; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, NH- OH, alkyl, CF ₃ , Cl, CN, or N ₃ ; Z ₁ and Z ₂ are each independently selected from C or a heteroatom; and R ₁ is phosphonate, monophosphate phosphonate, and diphosphate phosphonate, or various prodrugs (e.g., esters, McGuigan ProTides, diisoproxyl fumarate, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); (iii) at least one compound comprising a Flex-Cidofovir scaffold selected from:

, wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X ₁ , X ₂ , X ₃ , and X ₄ are each independently selected from C, O, N, or S; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, NH- OH, alkyl, CF ₃ , Cl, CN, or N ₃ ; Y ₃ is H, alkyl, NH ₂ , OH, O-alkyl, or NH-alkyl; W ₁ and W ₂ are each independently selected from H, alkyl, F, Cl, Br, I, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, COOH, CONH ₂ , or NHNH ₂ ; Z ₁ , Z ₂ , and Z ₃ are each independently selected from C or a heteroatom; and R ₁ is phosphonate, monophosphate phosphonate, and diphosphate phosphonate, or various prodrugs (e.g., esters, McGuigan ProTides, diisoproxyl fumarate, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); (iv) at least one compound comprising a Flex-BCNA scaffold selected from: , wherein R ₁ is H, NH ₂ , OH, O-alkyl, NH-alkyl, or F; R2 is H, NH2, OH, NHOH, O-alkyl, or NH-alkyl; R R ₄ is H, F, Cl, OH, CH ₃ , ethynyl, or prodrug ; R ₅ is H, monophosphate, diphosphate, triphosphate, various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); R ₆ is H, NH ₂ , OH, alkyl, F, Br, Cl, I, CN, CF ₃ , NO ₂ , O-alkyl, NH-alkyl, CO ₂ H, CONH ₂ , NHNH ₂ , esters or prodrugs; Z ₁ , Z ₂ , Z ₃ , Z ₄ , Z ₅ , and Z ₆ are each independently selected from C or N; and Y is null, CH ₂ , NH, O, vinyl, -NH(CH ₂ ) _n -, -O(CH ₂ ) _n -, ethynyl, wherein n = 1-4; (v) at least one compound comprising a fleximer selected from: wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X ₁ and X ₂ are each independently selected from C, O, N, or S; X ₃ is C or N; X ₄ is O NH S or CH ₂ ; W ₁ and W ₂ are each independently selected from H, F, alkyl, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, or amide; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, NH- OH, alkyl, CF ₃ , Cl, CN, or N ₃ ; Z ₁ and Z ₂ are each independently selected from C or a heteroatom; R ₁ is H or cyano; R ₂ and R ₃ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g., amino acid prodrugs); R ₄ is H, OH, N ₃ , or various prodrugs (e.g., amino acid prodrugs); R ₅ is H, F, ethynyl or cyano; and R ₆ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); (vi) at least one reverse fleximer D-nucleoside selected from: , wherein X ₁ ,X _{2 ,} X ₃ ,and X ₄ are each independently selected from C, O, N, or S; X ₅ is O, NH, S, or CH ₂ ; W ₁ and W ₂ are each independently selected from H, Cl, Br, I, F _, alkyl, CF ₃ , NH ₂ , OH, O- alkyl, NH-alkyl, cyano, amide, NO ₂ , CO ₂ H, CONH ₂ , NHNH ₂ , esters or prodrugs; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, alkyl, CF ₃ , N ₃ , Cl, or CN; Y ₃ is H, alkyl, NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g., amino acid prodrugs); R ₃ is H, OH, N ₃ , or various prodrugs (e.g., amino acid prodrugs); R ₄ is H, F, ethynyl, or cyano; L is null, NH, CH ₂ , O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; and R ₅ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); or , wherein X ₁ , X ₂ , X ₃ and X ₄ are each independently selected from C, O, N, or S; X ₅ is O, NH, S, or CH ₂ ; W ₁ and W ₂ are each independently selected from H, F, Cl, Br, I, alkyl, CF ₃ , NH ₂ , OH, O- alkyl, NH-alkyl, cyano, amide, CO ₂ H, CONH ₂ , NHNH ₂ , NO ₂ , esters or prodrugs; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, alkyl, CF ₃ , N ₃ , Cl, or CN; Y ₃ is H, CH ₃ , NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g., amino acid prodrugs); R ₃ is H, F, ethynyl, or cyano; L is null, NH, CH ₂ , O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; and R4 is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); (vii) at least one proximal reverse fleximer L-nucleoside selected from:

, wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X1, X2, X3, and X4 are each independently selected from C, O, N, or S; X ₅ is O, NH, S, or CH ₂ ; W ₁ and W ₂ are each independently selected from H, F, Cl, Br, I, alkyl, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, amide, CO ₂ H, CONH ₂ , NHNH ₂ , NO ₂ , esters or prodrugs; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, NH- OH, alkyl, CF ₃ , Cl, CN, or N ₃ ; Y ₃ is H, alkyl, NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g., amino acid prodrugs); R ₃ is H, OH, N ₃ , or various prodrugs (e.g., amino acid prodrugs); R ₄ is H, F, methyl, ethynyl, azido or cyano; and R ₅ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); or , wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X ₁ , X ₂ , X ₃ , and X ₄ are each independently selected from C, O, N, or S; X ₅ is CH ₂ , O, NH, or S; W ₁ and W ₂ are each independently selected from H, F, Br, Cl, I, alkyl, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, amide, NO ₂ , CO ₂ H, CONH ₂ , or NHNH ₂ ; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, NH- OH, alkyl, CF ₃ , Cl, CN, or N ₃ ; Y ₃ is H, alkyl, NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g., amino acid prodrugs); R ₃ is H, F, ethynyl or cyano; and R ₄ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); and (viii) at least one distal reverse fleximer L-nucleoside selected from: wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X ₁ , X ₂ , X ₃ , and X ₄ are each independently selected from C, O, N, or S; X ₅ is O, NH, S, or CH ₂ ; W ₁ and W ₂ are each independently selected from H, F, Cl, Br, I, alkyl, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, COOH, CONH ₂ , or NHNH ₂ ; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, or NH- OH, alkyl, CF ₃ , N ₃ , Cl, CN; Y ₃ is H, alkyl, NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl _, alkyl, ethynyl, or various prodrugs (e.g. amino acid prodrugs); R ₃ is H, OH, N ₃ , or various prodrugs (e.g., amino acid prodrugs); R ₄ is H, F, ethynyl or cyano; and R ₅ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); or wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X ₁ , X ₂ , X ₃ , and X ₄ are each independently selected from C, O, N, or S; X ₅ is CH ₂ , O, NH, or S; W ₁ and W ₂ are each independently selected from H, F, Br, Cl, I, alkyl, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, amide, NO2, CO2H, CONH2, or NHNH2; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, NH- OH, alkyl, CF3, Cl, CN, or N3; Y ₃ is H, CH ₃ , NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g. amino acid prodrugs); R ₃ is H, F, ethynyl or cyano; and R ₄ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs), or a pharmaceutically acceptable salt, isomer, hydrate, prodrug or solvate thereof. [0034] In some embodiments of the first aspect, the flexible nucleoside analogue comprises at least one of: , wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X ₁ , X ₂ , X ₃ , and X ₄ are each independently selected from C, O, N, or S; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, NH- OH, alkyl, CF ₃ , Cl, CN, or N ₃ ; Y ₃ is H, alkyl, NH ₂ , OH, O-alkyl, or NH-alkyl; W ₁ and W ₂ are each independently selected from H, alkyl, F, Cl, Br, I, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, COOH, CONH ₂ , or NHNH ₂ ; Z ₁ , Z ₂ , and Z ₃ are each independently selected from C or a heteroatom; and R ₁ is phosphonate, monophosphate phosphonate, and diphosphate phosphonate, or various prodrugs (e.g., esters, McGuigan ProTides, diisoproxyl fumarate, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs), or a pharmaceutically acceptable salt, isomer, hydrate, prodrug or solvate thereof. In some embodiments, X ₁ = X ₃ = N and X ₂ =X ₄ = C. In some embodiments, Z ₁ = Z ₂ = N and Z ₃ = C. In some embodiments, L is null. In some embodiments, X ₁ = X ₃ = N, X ₂ =X ₄ = C, Z ₁ = Z ₂ = N and Z ₃ = C. In some embodiments, X ₁ = X ₃ = N, X ₂ =X ₄ = C, and L is null. In some embodiments, Z ₁ = Z ₂ = N, Z ₃ = C and L is null. In some embodiments, X ₁ = X ₃ = N, X ₂ =X ₄ = C, Z ₁ = Z ₂ = N, Z ₃ = C, and L is null. [0035] In some embodiments of the first aspect, the flexible nucleoside analogue comprises at least one of: , wherein R ₁ is H, NH ₂ , OH, O-alkyl, NH-alkyl, or F; R ₂ is H, NH ₂ , OH, NHOH, O-alkyl, or NH-alkyl; R ₃ is H, OH, F, Cl, CH ₃ , ethynyl, or prodrug; R ₄ is H, F, Cl, OH, CH ₃ , ethynyl, or prodrug ; R ₅ is H, monophosphate, diphosphate, triphosphate, various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); R ₆ is H, NH ₂ , OH, alkyl, F, Br, Cl, I, CN, CF ₃ , NO ₂ , O-alkyl, NH-alkyl, CO ₂ H, CONH ₂ , NHNH ₂ , esters or prodrugs; Z ₁ , Z ₂ , Z ₃ , Z ₄ , Z ₅ , and Z ₆ are each independently selected from C or N; and Y is null, CH ₂ , NH, O, vinyl, -NH(CH ₂ ) _n -, -O(CH ₂ ) _n -, ethynyl, wherein n = 1-4, or a pharmaceutically acceptable salt, isomer, hydrate, prodrug or solvate thereof. In some embodiments, Z ₁ = Z ₂ = N. In some embodiments, Y is null. In some embodiments, Z ₁ = Z ₂ = N and Y is null. In some embodiments, one of Z ₃ , Z ₄ , Z ₅ or Z ₆ is N while the other three are C. In some embodiments, Z ₃ = Z ₅ = N and Z ₄ = Z ₆ = C. In some embodiments, Z ₄ = Z ₆ = N and Z ₃ = Z ₅ = C. In some embodiments, one of Z ₃ , Z ₄ , Z ₅ or Z ₆ is N while the other three are C, and Z ₁ = Z ₂ = N. In some embodiments, one of Z ₃ , Z ₄ , Z ₅ or Z ₆ is N while the other three are C, and L is null. In some embodiments, one of Z ₃ , Z ₄ , Z ₅ or Z ₆ is N while the other three are C, Z ₁ = Z ₂ = N and L is null. In some embodiments, (i) Z ₄ = Z ₆ = N and Z ₃ = Z ₅ = C or Z ₃ = Z ₅ = N and Z ₄ = Z ₆ = C, and (ii) Z ₁ = Z ₂ = N. In some embodiments, (i) Z ₄ = Z ₆ = N and Z ₃ = Z ₅ = C or Z ₃ = Z ₅ = N and Z ₄ = Z ₆ = C, and (ii) L is null. In some embodiments, (i) Z ₄ = Z ₆ = N and Z ₃ = Z ₅ = C or Z ₃ = Z ₅ = N and Z ₄ = Z ₆ = C, (ii) Z ₁ = Z ₂ = N, and (iii) L is null. [0036] In some embodiments of the first aspect, the flexible nucleoside analogue comprises at least one of:

, wherein X ₁ ,X _{2 ,} X ₃ ,and X ₄ are each independently selected from C, O, N, or S; X ₅ is O, NH, S, or CH ₂ ; W ₁ and W ₂ are each independently selected from H, Cl, Br, I, F _, alkyl, CF ₃ , NH ₂ , OH, O- alkyl, NH-alkyl, cyano, amide, NO ₂ , CO ₂ H, CONH ₂ , NHNH ₂ , esters or prodrugs; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, alkyl, CF ₃ , N ₃ , Cl, or CN; Y ₃ is H, alkyl, NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g., amino acid prodrugs); R ₃ is H, OH, N ₃ , or various prodrugs (e.g., amino acid prodrugs); R ₄ is H, F, ethynyl, or cyano; L is null, NH, CH ₂ , O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; and R ₅ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); or , wherein X ₁ , X ₂ , X ₃ and X ₄ are each independently selected from C, O, N, or S; X ₅ is O, NH, S, or CH ₂ ; W ₁ and W ₂ are each independently selected from H, F, Cl, Br, I, alkyl, CF ₃ , NH ₂ , OH, O- alkyl, NH-alkyl, cyano, amide, CO ₂ H, CONH ₂ , NHNH ₂ , NO ₂ , esters or prodrugs; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, alkyl, CF ₃ , N ₃ , Cl, or CN; Y ₃ is H, CH ₃ , NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g., amino acid prodrugs); R ₃ is H, F, ethynyl, or cyano; L is null, NH, CH ₂ , O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; and R ₄ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs), or a pharmaceutically acceptable salt, isomer, hydrate, prodrug or solvate thereof. In some embodiments, X ₁ = X ₃ = N and X ₂ =X ₄ = C. In some embodiments, Z ₁ = Z ₂ = N and W ₃ = C. In some embodiments, L is null. In some embodiments, X ₁ = X ₃ = N, X ₂ =X ₄ = C, Z ₁ = Z ₂ = N and W ₃ = C. In some embodiments, X ₁ = X ₃ = N, X ₂ =X ₄ = C, and L is null. In some embodiments, Z ₁ = Z ₂ = N, W ₃ = C and L is null. In some embodiments, X ₁ = X ₃ = N, X ₂ =X ₄ = C, Z ₁ = Z ₂ = N, W ₃ = C, and L is null. [0037] In some embodiments of the first aspect, the flexible nucleoside analogue comprises at least one of: , wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 14; X ₁ , X ₂ , X ₃ , and X ₄ are each independently selected from C, O, N, or S; X ₅ is O, NH, S, or CH ₂ ; W ₁ and W ₂ are each independently selected from H, F, Cl, Br, I, alkyl, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, amide, CO ₂ H, CONH ₂ , NHNH ₂ , NO ₂ , esters or prodrugs; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, NH- OH, alkyl, CF ₃ , Cl, CN, or N ₃ ; Y ₃ is H, alkyl, NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g., amino acid prodrugs); R ₃ is H, OH, N ₃ , or various prodrugs (e.g., amino acid prodrugs); R ₄ is H, F, methyl, ethynyl, azido or cyano; and R ₅ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs), or a pharmaceutically acceptable salt, isomer, hydrate, prodrug or solvate thereof. In some embodiments, X ₁ = X ₃ = N and X ₂ =X ₄ = C. In some embodiments, X ₁ = O or S and X ₂ = X ₃ =X4 = C. In some embodiments, X5 = O. In some embodiments, Z1 = Z2 = N and W3 = C. In some embodiments, L is null. In some embodiments, R ₃ = OH. In some embodiments, X ₁ = X ₃ = N, X ₂ =X ₄ = C, Z ₁ = Z ₂ = N and W ₃ = C. In some embodiments, X ₁ = X ₃ = N, X ₂ =X ₄ = C, and L is null. In some embodiments, Z ₁ = Z ₂ = N, W ₃ = C and L is null. In some embodiments, X ₁ = X ₃ = N, X ₂ =X ₄ = C, Z ₁ = Z ₂ = N, W ₃ = C, and L is null. In some embodiments, X ₁ = O or S and X ₂ = X ₃ =X ₄ = C and X ₅ = O. In some embodiments, X ₁ = O or S and X ₂ = X ₃ =X ₄ = C, Z ₁ = Z ₂ = N and W ₃ = C. In some embodiments, X ₁ = O or S and X ₂ = X ₃ =X ₄ = C and L = null. In some embodiments, X ₁ = O or S and X ₂ = X ₃ =X ₄ = C and R ₃ = OH. In some embodiments, X ₅ = O, Z ₁ = Z ₂ = N and W ₃ = C. In some embodiments, X ₅ = O and L = null. In some embodiments, X ₅ = O and R ₃ = OH. In some embodiments, X ₁ = O or S, X ₂ = X ₃ =X ₄ = C, X ₅ = O, and L = null. In some embodiments, X ₁ = O or S, X ₂ = X ₃ =X ₄ = C, X ₅ = O, L = null, and R ₃ = OH. In some embodiments, X ₁ = O or S, X ₂ = X ₃ =X ₄ = C, X ₅ = O, L = null, R ₃ = OH, Z ₁ = Z ₂ = N and W ₃ = C. [0038] In some embodiments of the first aspect, the flexible nucleoside analogue comprises at least one of:

, wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X ₁ , X ₂ , X ₃ , and X ₄ are each independently selected from C, O, N, or S; X ₅ is CH ₂ , O, NH, or S; W ₁ and W ₂ are each independently selected from H, F, Br, Cl, I, alkyl, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, amide, NO ₂ , CO ₂ H, CONH ₂ , or NHNH ₂ ; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, NH- OH, alkyl, CF ₃ , Cl, CN, or N ₃ ; Y ₃ is H, alkyl, NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g., amino acid prodrugs); R ₃ is H, F, ethynyl or cyano; and R ₄ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs), or a pharmaceutically acceptable salt, isomer, hydrate, prodrug or solvate thereof. In some embodiments, X ₁ = X ₃ = N and X ₂ =X ₄ = C. In some embodiments, X ₁ = O or S and X ₂ = X ₃ =X ₄ = C. In some embodiments, X ₅ = O or S. In some embodiments, Z ₁ = Z ₂ = N and W ₃ = C. In some embodiments, L is null. In some embodiments, X1 = X3 = N, X2 =X4 = C, Z1 = Z2 = N and W3 = C. In some embodiments, X ₁ = X ₃ = N, X ₂ =X ₄ = C, and L is null. In some embodiments, Z ₁ = Z ₂ = N, W ₃ = C and L is null. In some embodiments, X ₁ = X ₃ = N, X ₂ =X ₄ = C, Z ₁ = Z ₂ = N, W ₃ = C, and L is null. In some embodiments, X ₁ = O or S and X ₂ = X ₃ =X ₄ = C and X ₅ = O or S. In some embodiments, X ₁ = O or S and X ₂ = X ₃ =X ₄ = C, Z ₁ = Z ₂ = N and W ₃ = C. In some embodiments, X ₁ = O or S and X ₂ = X ₃ =X ₄ = C, X ₅ is O or S, and L = null. In some embodiments, X ₅ = O or S, Z ₁ = Z ₂ = N and W ₃ = C. In some embodiments, X ₅ = O or S and L = null. In some embodiments, X ₁ = O or S, X ₂ = X ₃ =X ₄ = C, X ₅ = O or S L = null Z ₁ = Z ₂ = N and W ₃ = C [0039] In some embodiments of the first aspect, the flexible nucleoside analogue comprises at least one of: wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X ₁ , X ₂ , X ₃ , and X ₄ are each independently selected from C, O, N, or S; X5 is O, NH, S, or CH2; W ₁ and W ₂ are each independently selected from H, F, Cl, Br, I, alkyl, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, COOH, CONH ₂ , or NHNH ₂ ; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, or NH- OH, alkyl, CF ₃ , N ₃ , Cl, CN; Y ₃ is H, alkyl, NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl _, alkyl, ethynyl, or various prodrugs (e.g. amino acid prodrugs); R ₃ is H, OH, N ₃ , or various prodrugs (e.g., amino acid prodrugs); R ₄ is H, F, ethynyl or cyano; and R ₅ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); or

wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X ₁ , X ₂ , X ₃ , and X ₄ are each independently selected from C, O, N, or S; X ₅ is CH ₂ , O, NH, or S; W ₁ and W ₂ are each independently selected from H, F, Br, Cl, I, alkyl, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, amide, NO ₂ , CO ₂ H, CONH ₂ , or NHNH ₂ ; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, NH- OH, alkyl, CF ₃ , Cl, CN, or N ₃ ; Y ₃ is H, CH ₃ , NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g. amino acid prodrugs); R ₃ is H, F, ethynyl or cyano; and R ₄ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs), or a pharmaceutically acceptable salt, isomer, hydrate, prodrug or solvate thereof. In some embodiments, X ₁ = X ₂ = N. In some embodiments, Z ₁ = Z ₂ = N and W ₃ = C. In some embodiments, L is null. In some embodiments, X ₁ = X ₂ = N, Z ₁ = Z ₂ = N and W ₃ = C. In some embodiments, X ₁ = X ₂ = N and L is null. In some embodiments, Z ₁ = Z ₂ = N, W ₃ = C and L is null. In some embodiments, X ₁ = X ₂ = N, Z ₁ = Z ₂ = N, W ₃ = C, and L is null. [0040] In some embodiments of the first aspect, the flexible nucleoside analogue comprises at least one of:

wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X ₁ , X ₂ , X ₃ , and X ₄ are each independently selected from C, O, N, or S; X ₅ is O, NH, S, or CH ₂ ; W ₁ and W ₂ are each independently selected from H, F, Cl, Br, I, alkyl, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, amide, CO ₂ H, CONH ₂ , NHNH ₂ , or NO ₂ , esters or prodrugs; W3 is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, NH- OH, alkyl, CF ₃ , Cl, CN, or N ₃ ; Y ₃ is H, alkyl, NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g., amino acid prodrugs); R ₃ is H, OH, N ₃ , or various prodrugs (e.g., amino acid prodrugs); R ₄ is H, F, ethynyl or cyano; and R ₅ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs), or a pharmaceutically acceptable salt, isomer, hydrate, prodrug or solvate thereof. [0041] In some embodiments of the first aspect, the flexible nucleoside analogue comprises at least one of:

wherein L is null; X ₁ is selected from O or S; X ₂ , X ₃ , and X ₄ are each C; X ₅ is O; W ₁ and W ₂ are each independently selected from H and alkyl; W ₃ is C; Y ₁ and Y ₂ are each independently selected from OH, NH ₂ , H; Y ₃ is H; Z ₁ and Z ₂ are each N; R ₁ and R ₂ are each H; R3 is OH; R ₄ is H; and R ₅ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs), or a pharmaceutically acceptable salt, isomer, hydrate, prodrug or solvate thereof. [0042] In some embodiments of the first aspect, the flexible nucleoside analogue comprises at least one of: , wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X ₁ , X ₂ , X ₃ , and X ₄ are each independently selected from C, O, N, or S; X ₅ is CH ₂ , O, NH, or S; W ₁ and W ₂ are each independently selected from H, F, Br, Cl, I, alkyl, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, amide, NO ₂ , CO ₂ H, CONH ₂ , NHNH ₂ , esters or prodrugs; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, NH- OH, alkyl, CF ₃ , Cl, CN, or N ₃ ; Y ₃ is H, alkyl, NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g., amino acid prodrugs); R ₃ is H, F, ethynyl or cyano; and R ₄ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs), or a pharmaceutically acceptable salt, isomer, hydrate, prodrug or solvate thereof. [0043] In some embodiments of the first aspect, the flexible nucleoside analogue comprises at least one of: , wherein L is null; X ₁ is O or S; X ₂ , X ₃ , and X ₄ are each C; X ₅ is O or S; W ₁ and W ₂ are each independently selected from H or alkyl; W ₃ is C; Y d Y h i d d tl l t d f H NH OH Y ₃ is H; Z ₁ and Z ₂ are each N; R ₁ , R ₂ and R ₃ are each H; and R ₄ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs), or a pharmaceutically acceptable salt, isomer, hydrate, prodrug or solvate thereof. [0044] In some embodiments of the first aspect, the flexible nucleoside analogue comprises at least one of: (A) 5-(furan-2-yl)-1-((2S,4R,5S)-4-hydroxy-5-(hydroxymethyl)tetr ahydrofuran-2-yl)pyrimidine- 2,4(1H,3H)-dione (CHK-01); (B) 1-((2S,4R,5S)-4-hydroxy-5-(hydroxymethyl)tetrahydrofuran-2-y l)-5-(thiophen-2- yl)pyrimidine-2,4(1H,3H)-dione (CHK-02); (C) 1-((2S,4R,5S)-4-hydroxy-5-(hydroxymethyl)tetrahydrofuran-2-y l)-5-(5-methylthiophen-2- yl)pyrimidine-2,4(1H,3H)-dione (CHK-03); (D) 1-((2S,4R,5S)-4-hydroxy-5-(hydroxymethyl)tetrahydrofuran-2-y l)-5-(5-methylfuran-2- yl)pyrimidine-2,4(1H,3H)-dione (CHK-04); (E) 4-amino-5-(furan-2-yl)-1-((2S,4R,5S)-4-hydroxy-5-(hydroxymet hyl)tetrahydrofuran-2-yl)pyrimidin- 2(1H)-one (CHK-05);(F) 4-amino-1-((2S,4R,5S)-4-hydroxy-5-(hydroxymethyl)tetrahydrof uran-2-yl)-5-(thiophen-2- yl)pyrimidin-2(1H)-one (CHK-06); (G) 4-amino-1-((2S,4R,5S)-4-hydroxy-5-(hydroxymethyl)tetrahydrof uran-2-yl)-5-(5- methylthiophen-2-yl)pyrimidin-2(1H)-one (CHK-07); (H) 4-amino-1-((2S,4R,5S)-4-hydroxy-5-(hydroxymethyl)tetrahydrof uran-2-yl)-5-(5- methylfuran-2-yl)pyrimidin-2(1H)-one (CHK-08); and (I) 4-amino-5-(furan-2-yl)-1-((2R,5S)-2-(hydroxymethyl)-1,3-oxat hiolan-5-yl)pyrimidin-2(1H)- one (CHK-50), or a pharmaceutically acceptable salt, isomer, hydrate, prodrug or solvate thereof. [0045] In some embodiments of the first aspect, the flexible nucleoside analogue comprises at least one of:

wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X ₁ and X ₂ are each independently selected from C, O, N, or S; X ₃ is C or N; X ₄ is O, NH, S, or CH ₂ ; W ₁ and W ₂ are each independently selected from H, F, alkyl, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, or amide; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, NH- OH, alkyl, CF ₃ , Cl, CN, or N ₃ ; Z ₁ and Z ₂ are each independently selected from C or a heteroatom; R ₁ is H or cyano; R ₂ and R ₃ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g., amino acid prodrugs); R ₄ is H, OH, N ₃ , or various prodrugs (e.g., amino acid prodrugs); R ₅ is H, F, ethynyl or cyano; and R ₆ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs), or a pharmaceutically acceptable salt, isomer, hydrate, prodrug or solvate thereof. In some embodiments, X ₁ = X ₃ = N and X ₂ is C. In some embodiments, Z ₁ = Z ₂ = N. In some embodiments, W ₁ = W ₂ = H. In some embodiments, R ₂ is CH ₃ , R ₃ is F, R ₄ is OH and/or R ₅ is H. In some embodiments, L is null. In some embodiments, X ₁ = X ₃ = N, X ₂ is C, and Z ₁ = Z ₂ = N. In some embodiments, X ₁ = X ₃ = N, X ₂ is C, and W ₁ = W ₂ = H. In some embodiments, X ₁ = X ₃ = N, X ₂ is C, and R ₂ is CH ₃ , R ₃ is F, R ₄ is OH and/or R ₅ is H. In some embodiments, X ₁ = X ₃ = N, X ₂ is C, and L is null. In some embodiments, R ₂ is CH ₃ , R ₃ is F, R ₄ is OH and/or R ₅ is H and Z ₁ = Z ₂ = N. In some embodiments, R ₂ is CH ₃ , R ₃ is F, R ₄ is OH and/or R ₅ is H and W ₁ = W ₂ = H. In some embodiments, R ₂ is CH ₃ , R ₃ is F, R ₄ is OH and/or R ₅ is H and L is null. In some embodiments, Z ₁ = Z ₂ = N and L is null. In some embodiments, Z ₁ = Z ₂ = N and W ₁ = W ₂ = H. In some embodiments, W ₁ = W ₂ = H and L is null. In some embodiments, X ₁ = X ₃ = N, X ₂ is C, Z ₁ = Z ₂ = N, W ₁ = W ₂ = H, R ₂ is CH ₃ , R ₃ is F, R ₄ is OH and/or R ₅ is H, and L is null. Compositions comprising the flexible nucleoside analogues described herein [0046] The fleximer and reverse fleximer nucleoside analogues described herein may be administered in various ways and in various forms. In some embodiments, the fleximer or reverse fleximer nucleoside analogues described herein may be administered systemically, orally (including buccal or sublingual), topically, by inhalation (or spray) or by injection (e.g., intravenously, intramuscularly, subcutaneously, intravasularly, intrathecally, intradermally, intra-arterially). For the injections, the fleximer or reverse fleximer nucleoside analogues are generally present in the form of liquid suspensions, which can be injected by means of syringes or infusions, for example. In this regard, the fleximer or reverse fleximer nucleoside analogues described herein are generally dissolved in solutions that can be buffered, isotonic, physiological, and/or saline, and which are compatible with pharmaceutical use and known to those skilled in the art. [0047] Accordingly, in a second aspect, a composition formulated for therapeutic use is described, wherein the composition comprises, consists of, or consists essentially of at least one fleximer or reverse fleximer nucleoside analogue of the first aspect, and at least one pharmaceutically acceptable carrier, excipient, or diluent. The pharmaceutical composition will typically be formulated in a format suitable for administration to the subject, for example, as a syrup, elixir, tablet, troche, lozenge, hard or soft capsule, pill, suppository, oily or aqueous suspension, dispersible powder or granule, emulsion, injectable, solution, sustained release formulation, or aerosol. Some examples of acceptable excipients are those that are non-toxic, will aid administration to the patient, and do not adversely affect the therapeutic benefit of the fleximer or reverse fleximer nucleoside analogue compound. Such excipient may be a solid, liquid, semi-solid or, in the case of an aerosol composition, a gaseous excipient, that is generally include, but are not limited to, starch, cellulose, talc, glucose, lactose, sucrose, gelatin, malt, rice, flour, chalk, silica gel, magnesium stearate, sodium stearate, glycerol monostearate, sodium chloride, dried skim milk and the like. Liquid and semisolid excipients include, but are not limited to, glycerol, propylene glycol, water, ethanol, and various oils, including those of petroleum, animal, vegetable, or synthetic origin, e.g., peanut oil, soybean oil, mineral oil, sesame oil, etc. Preferred liquid carriers, particularly for injectable solutions, include, but are not limited to, water, saline, aqueous dextrose, and glycols. Liquid compositions may contain one or more agents or carriers chosen from dispersants, solubilizing agents, stabilizers, preservatives, and any combination thereof. Agents or carriers which can be used in liquid and/or injectable formulations include, but are not limited to, methylcellulose, hydroxymethylcellulose, carboxymethylcellulose, polysorbate 80, mannitol, gelatin, lactose, vegetable oils, and acacia. Other suitable pharmaceutical excipients and their formulations are described in Remington's Pharmaceutical Sciences, edited by E. W. Martin (Mack Publishing Company, 18th ed., 1990). [0048] The amount of a fleximer or reverse fleximer nucleoside analogue of the first aspect in the composition can vary within the full range employed by those skilled in the art. In some embodiments, a composition may contain, on a weight percent (wt %) basis, from about 0.01-99.99 wt % of a fleximer or reverse fleximer nucleoside analogue, based on the total weight of the composition, with the balance being one or more suitable pharmaceutical excipients. In some embodiments, the composition comprises an amount of a fleximer or reverse fleximer nucleoside analogue of the first aspect of between 5 μg and 1000 mg, preferably between 1 and 500 mg, preferably between 5 and 100 mg. The ratio between the amounts by weight of a fleximer or reverse fleximer nucleoside analogue and of pharmaceutically acceptable carrier is between 5/95 and 95/5, preferably between 20/80 and 80/20. [0049] The fleximer or reverse fleximer nucleoside analogues may be the only active ingredients in the composition of the second aspect, or they may be combined with other active ingredients. Accordingly, in some embodiments of the second aspect, the composition may comprise, consist of, or consist essentially of at least one fleximer or reverse fleximer nucleoside analogue of the first aspect, at least one other pharmaceutically active agent, e.g., at least one other medicament used for the treatment of viral infection, and at least one pharmaceutically acceptable carrier, excipient, or diluent. In some embodiments, the composition may comprise, or be combined with, one or more other antivirals or antiretrovirals (e.g., nucleoside or nucleotide and non-nucleoside inhibitors, protease inhibitors, entry inhibitors, integrase inhibitors, etc.). Methods of using [0050] In a third aspect, a method for treating and/or preventing a filoviral, flaviviral, herpesviral, alphaviral, polyomaviral, enteroviral, matonaviral, phenuiviral, Hepatitis B viral, and/or coronaviral infection is described, comprising the administration, to a patient, of an effective amount of at least one fleximer o (i.e., a composition of the second aspect). In some embodiments, the fleximer or reverse fleximer nucleoside analogues, as active agents, will be administered in a therapeutically effective amount by any of the accepted modes of administration for agents that serve similar utilities. The “effective amount” will be an amount of a fleximer or reverse fleximer nucleoside analogue, as described herein, that would be understood by one skilled in the art to provide therapeutic benefits. The active agent can be administered once a week, two or more times per week, once a day, or more than once a day. As indicated above, all of the factors to be considered in determining the effective amount will be well within the skill of the attending clinician or other health care professional. In some embodiments, therapeutically effective amounts of a fleximer or reverse fleximer nucleoside analogue, as described herein, may range from approximately 0.05 to 50 mg per kilogram body weight of the subject per day; preferably about 0.1-25 mg/kg/day, more preferably from about 0.5 to 10 mg/kg/day. Thus, for administration to a 70 kg person, the dosage range would most preferably be about 35-700 mg per day. [0051] In some embodiments of the third aspect, a method for treating and/or preventing a viral infection in a subject is described, wherein the viral infection is caused by at least one of a coronavirus, a herpesvirus, an alphavirus, a polyomavirus, an enterovirus, a filovirus, a matonavirus, a phenuivirus, a Hepatitis B virus, and/or a flavivirus, comprising administration, to the subject, of a therapeutically effective amount of at least one fleximer or reverse fleximer nucleoside analogue selected from the first aspect described herein, or a composition of the second aspect described herein. In some embodiments, a therapeutically effective amount of the fleximer or reverse fleximer nucleoside analogue is from 0.05 to 50 mg per kilogram body weight of the subject per day. In some embodiments, the fleximer or reverse fleximer nucleoside analogue is present in, and administered as, a composition, as described in the second aspect herein. In some embodiments, the viral infection is caused by a coronavirus. In some embodiments, the viral infection is caused by a herpesvirus. In some embodiments, the viral infection is caused by an alphavirus. In some embodiments, the viral infection is caused by a polyomavirus. In some embodiments, the viral infection is caused by an enterovirus. In some embodiments, the viral infection is caused by a filovirus. In some embodiments, the viral infection is caused by a matonavirus. In some embodiments, the viral infection is caused by a phenuivirus. In some embodiments, the viral infection is caused by a Hepatitis B virus. In some embodiments, the viral infection is caused by a flavivirus. In some embodiments, the method of administration is selected from systemically, orally, buccally, sublingually, topically, by inhalation, by spraying, intravenously, intramuscularly, subcutaneously, intrathecally, intradermally, intravascularly or intra-arterially. [0052] In some embodiments of the third aspect, a method of treating and/or reducing the effects of Epstein Barr virus in a subject in need of such treatment is described, the method comprising administering to the subject a therapeutically effective amount of a reverse fleximer nucleoside analogue selected from: CHK-05 CHK-03 , and a pharmaceutically acceptable salt, isomer, hydrate, prodrug or solvate thereof. In some embodiments, a therapeutically effective amount of the reverse fleximer nucleoside analogue is from 0.05 to 50 mg per kilogram body weight of the subject per day. [0053] In some embodiments of the third aspect, a method of treating and/or reducing the effects of a coronavirus, enterovirus, Chikungunya virus, Ebola virus and/or Dengue virus in a subject in need of such treatment is described, the method comprising administering to the subject a therapeutically effective amount of a reverse fleximer nucleoside analogue having the following structure: and a pharmaceutically acceptable salt, isomer, hydrate, prodrug or solvate thereof. In some embodiments, a therapeutically effective amount of the reverse fleximer nucleoside analogue is from 0.05 to 50 mg per kilogram body weight of the subject per day. [0054] In some embodiments of the fourth aspect, a method of treating and/or reducing the effects of Ebola virus in a subject in need of such treatment is described, the method comprising administering to the subject a therapeutically effective amount of a reverse fleximer nucleoside analogue selected from: CHK-05 and a pharmaceutically acceptable salt, isomer, hydrate, prodrug or solvate thereof. In some embodiments, a therapeutically effective amount of the reverse fleximer nucleoside analogue is from 0.05 to 50 mg per kilogram body weight of the subject per day. [0055] In some embodiments of the third aspect, a method of treating and/or reducing the effects of Hepatitus B virus in a subject in need of such treatment is described, the method comprising administering to the subject a therapeutically effective amount of a proximal reverse fleximer L- nucleoside having the following structure: , wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X ₁ , X ₂ , X ₃ , and X ₄ are each independently selected from C, O, N, or S; X ₅ is O, NH, S, or CH ₂ ; W ₁ and W ₂ are each independently selected from H, F, Cl, Br, I, alkyl, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, amide, CO ₂ H, CONH ₂ , NHNH ₂ , NO ₂ , esters or prodrugs; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, NH- OH, alkyl, CF ₃ , Cl, CN, or N ₃ ; Y ₃ is H, alkyl, NH ₂ , OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g., amino acid prodrugs); R ₃ is H, OH, N ₃ , or various prodrugs (e.g., amino acid prodrugs); R ₄ is H, F, methyl, ethynyl, azido or cyano; and R ₅ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs); or

, wherein L is null, CH ₂ , NH, O, vinyl, ethynyl, -O-(CH ₂ ) _n -, or -NH-(CH ₂ ) _n -; n is any integer from 1-4; X ₁ , X ₂ , X ₃ , and X ₄ are each independently selected from C, O, N, or S; X ₅ is CH ₂ , O, NH, or S; W ₁ and W ₂ are each independently selected from H, F, Br, Cl, I, alkyl, CF ₃ , NH ₂ , OH, O-alkyl, NH-alkyl, cyano, amide, NO ₂ , CO ₂ H, CONH ₂ , or NHNH ₂ ; W ₃ is C or N; Y ₁ and Y ₂ are each independently selected from H, OH, SH, F, NH ₂ , NH-alkyl, O-alkyl, NH- OH, alkyl, CF ₃ , Cl, CN, or N ₃ ; Y3 is H, alkyl, NH2, OH, O-alkyl, or NH-alkyl; Z ₁ and Z ₂ are each independently selected from C or N; R ₁ and R ₂ are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g., amino acid prodrugs); R ₃ is H, F, ethynyl or cyano; and R ₄ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs), or a pharmaceutically acceptable salt, isomer, hydrate, prodrug or solvate thereof. [0056] In some embodiments of the third aspect, a method of treating and/or reducing the effects of Hepatitus B virus in a subject in need of such treatment is described, the method comprising administering to the subject a therapeutically effective amount of a proximal reverse fleximer L- nucleoside having the following structure:

wherein L is null; X ₁ is selected from O or S; X ₂ , X ₃ , and X ₄ are each C; X ₅ is O; W ₁ and W ₂ are each independently selected from H and alkyl; W ₃ is C; Y ₁ and Y ₂ are each independently selected from OH, NH ₂ , H; Y ₃ is H; Z ₁ and Z ₂ are each N; R ₁ and R ₂ are each H; R ₃ is OH; R ₄ is H; and R5 is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs), or a pharmaceutically acceptable salt, isomer, hydrate, prodrug or solvate thereof. [0057] In some embodiments of the third aspect, a method of treating and/or reducing the effects of Hepatitus B virus in a subject in need of such treatment is described, the method comprising administering to the subject a therapeutically effective amount of a proximal reverse fleximer L- nucleoside having the following structure:

, wherein L is null; X ₁ is O or S; X2, X3, and X4 are each C; X ₅ is O or S; W ₁ and W ₂ are each independently selected from H or alkyl; W ₃ is C; Y ₁ and Y ₂ are each independently selected from H, NH ₂ , or OH; Y ₃ is H; Z ₁ and Z ₂ are each N; R ₁ , R ₂ and R ₃ are each H; and R ₄ is H, monophosphate, diphosphate, triphosphate, or various prodrugs (e.g., esters, McGuigan ProTides, lipid phosphates, lipid esters, HepDirect, amino acid prodrugs), or a pharmaceutically acceptable salt, isomer, hydrate, prodrug or solvate thereof. [0058] In some embodiments, the viral infection is caused by a coronavirus selected from human coronaviruses (HCoV), Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV), SARS-CoV- 2, and Middle East respiratory syndrome (MERS), and mutants thereof. In some embodiments, the viral infection is caused by a herpesvirus selected from herpes simplex virus 1, herpes simplex virus 2, varicella-zoster virus, Epstein-Barr virus, cytomegalovirus, Human herpesvirus-6, Human herpesvirus- 7, and Kaposi’s sarcoma herpes virus. In some embodiments, the viral infection is caused by an alphavirus selected from eastern equine encephalomyelitis (EEE), Venezuelan equine encephalomyelitis (VEE), and western equine encephalomyelitis (WEE). In some embodiments, the viral infection is caused by a polyomavirus. In some embodiments, the viral infection is caused by an enterovirus selected from echovirus and coxsackievirus. In some embodiments, the viral infection is caused by a filovirus selected from Zaire Ebola virus, Sudan Ebola virus, Reston Ebola virus, Cote d'Ivoire Ebola virus and Marburg virus. In some embodiments, the viral infection is caused by a matonavirus selected from Rubella, Rustrela, and Ruhugu. In some embodiments, the viral infection is caused by is caused by a flavivirus selected from the group consisting of yellow fever virus, Apoi virus, Aroa virus, Bagaza virus, Banzi virus, Bouboui virus, Bukalasa bat virus, Cacipacore virus, Carey Island virus, Cowbone Ridge virus, Dakar bat virus, dengue virus, Edge Hill virus, Entebbe bat virus, Gadgets Gully virus, Ilheus virus, Israel turkey meningoencephalomyelitis virus, Japanese encephalitis virus, Jugra virus, Jutiapa virus, Kadam virus, Kedougou virus, Kokobera virus, Koutango virus, Kyasanur Forest disease virus, Langat virus, Louping ill virus, Meaban virus, Modoc virus, Montana myotis leukoencephalitis virus, Murray Valley encephalitis virus, Ntaya virus, Omsk hemorrhagic fever virus, Phnom Phenh bat virus, Powassan virus, Rio Bravo virus, Royal Farm virus, Saboya virus, Sal Vieja virus, San Perlita virus, Saumarez Reef virus, Sepik virus, St. Louis encephalitis virus, Tembusu virus, tick-borne encephalitis virus, Tyuleniy virus, Uganda S virus, Usutu virus, Wesselsbron virus, West Nile virus, Yaounde virus, Yokose virus, Zika virus, cell fusing agent virus and Tamana bat virus. [0059] In some embodiments of the third aspect, a method for binding to, or interacting with, natural and/or mutated polymerases of a filovirus, flavivirus, alphaviruses, polyomaviruses, enteroviruses, herpesvirus, matonavirus, phenuivirus, Hepatitis B virus, or coronavirus to induce inhibition activity of said virus is described, the method comprising administering to the subject a therapeutically effective amount of at least one fleximer or reverse fleximer nucleoside analogue of the first aspect, or a composition including same (i.e., the second aspect described herein). Additional target enzymes include, but not limited to, various viral methyltransferases for all of the viruses, including the exonuclease (for CoVs), the RNA dependent RNA polymerases (RdRps) for all of the viruses, and the NiRAN (RdRp associated nucleotidyl transferase domain) for CoVs. [0060] In another aspect, a use of at least one fleximer or reverse fleximer nucleoside analogue of the first aspect, or a composition including same, in a medicament for medicine is described. In a more specific embodiment hereof, said use as a medicine is for the prevention or treatment of a filovirus, herpesvirus, flavivirus, alphavirus, polyomavirus, enterovirus, matonavirus, phenuivirus, Hepatitis B virus, and/or coronavirus in a subject, mammal or human. In some embodiments, a therapeutically effective amount of the fleximer or reverse fleximer nucleoside analogue is from 0.05 to 50 mg per kilogram body weight of the subject per day. In some embodiments, the use as a medicine is for the prevention or treatment of a coronavirus, SARS and MERS-CoV in a subject. In some embodiments, the use as a medicine is for the prevention or treatment of an infection of a COVID-19 coronavirus or a mutant thereof in a subject. In some embodiments, the use as a medicine is for the prevention or treatment of viruses including, but not limited to, filoviruses such as Ebola, Marburg and Sudan, and flaviviruses such as dengue, zika, yellow fever, and tickborne encephalitis, in a subject. In some embodiments, the use as a medicine is for the prevention or treatment of an infection of a Hepatitis B virus in a subject. [0061] In another aspect, the manufacture of a medicament comprising at least one fleximer or reverse fleximer nucleoside analogue of the first, or a composition including same (i.e., the second aspect described herein), for the treatment of a coronavirus, herpesvirus, alphaviruses, enteroviruses, filovirus, matonavirus, phenuivirus, Hepatitis B virus, and/or flavivirus is described. [0062] In another aspect, novel intermediates or prodrugs which are useful for preparing at least one fleximer or reverse fleximer nucleoside analogue of the first aspect or converted to active agents in vivo is described. Prodrugs are selected and prepared in order to improve some selected property of the molecule, such as water solubility or ability to cross a membrane, temporarily. Most common (biologically labile) functional groups utilized in prodrug design include, but are not limited to, carbonates, esters, amino acyl esters, amides, carbamates, oximes, imines, ethers, or phosphates. [0063] In a still further aspect, the present application provides for a method of treating a filovirus, flavivirus. alphaviruses, polyomaviruses, enteroviruses, herpesvirus, matonavirus, phenuivirus, Hepatitis B virus, or coronavirus in a patient, comprising administering to said patient a therapeutically effective amount of at least one fleximer or reverse fleximer nucleoside analogue of the first aspect, or a composition including same (i.e., the second aspect described herein), and at least one additional therapeutic agent having anti-viral properties. [0064] In another aspect, a method for treating a viral infection comprises the administration, to a patient, of an effective amount of at least one fleximer or reverse fleximer nucleoside analogue of the first aspect, or a composition including same (i.e., the second aspect described herein), is described. In some embodiments, the fleximer or reverse fleximer nucleoside analogue can be a prodrug or otherwise capable of releasing the active ingredient after in vivo metabolism. [0065] In another aspect, a method for treating a CoV viral infection is described, comprising the administration, to a patient, of an effective amount of at least one fleximer or reverse fleximer nucleoside analogue of the first aspect, or a composition including same. The fleximer or reverse fleximer nucleoside analogue can further be a prodrug or in form of capable of releasing the active ingredient after in vivo metabolism. [0066] In another aspect, a cell infected with a virus or to be infected with the virus is contacted with at least one fleximer or reverse fleximer nucleoside analogue of the first aspect, or a composition including same (i.e., the second aspect described herein), wherein the virus is selected from a filovirus, flavivirus. alphaviruses, polyomaviruses, enteroviruses, herpesvirus, matonavirus, phenuivirus, Hepatitis B virus, or coronavirus. In some embodiments, the amount of the at least one fleximer or reverse fleximer nucleoside analogue used is from about 1 μg/ml to about 40 μg/ml, and more preferably, from about 3 μg/ml to about 20 μg/ml. [0067] In another aspect, methods for synthesis, analysis, separation, isolation, purification, characterization, and testing of the compounds of the first aspect are provided. [0068] The features and advantages of the invention are more fully illustrated by the following non- limiting examples, wherein all parts and percentages are by weight, unless otherwise expressly stated. EXAMPL [0069] The following schematics show embodiments of a method of synthesis for reverse fleximer nucleoside analogues described herein: (A) ; (B ; (C

; and (D) . EXAMPLE 2 [0070] Synthesis schemes for mono-, di-, and triphosphates attached to lamivudine (3TC) analogues are set forth below: (A)

; and (B) . EXAMPLE 3 [0071] Below are embodiments of synthesis schemes as shown in Figure 1 herein. [0072] (2S,3R,5S)-5-(5-iodo-2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl )-2-(((4- methylbe To a suspension of 5-iodouracil (3.979 g, 16.72 mmol, 1.3 eq) in dichloroethane, N,O- Bis(trimethylsilyl)acetamide (6.3 mL, 25.73 mmol, 2.0 eq) was added. The reaction mixture was heated to 85 °C and refluxed under nitrogen until a clear solution was obtained (ca.30 minutes). The reaction mixture was cooled quickly to room temperature using an ice-water bath. Compound 1 (5.002 g, 12.6 mmol, 1.0 eq) was added and stirred at room temperature overnight. The reaction mixture was diluted with ethanol and allowed to stir for 10 minutes. Solvent was removed via rotary evaporation to yield crude product 2a ((2S,3R,5S)-5-(5-iodo-2,4-dioxo-3,4-dihydropyrimidin-1(2H)-y l)-2-(((4- methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl 4-methylbenzoate) as a yellow syrup. The purified product was obtained via flash chromatography (50% EtOAc:Hexanes) as a white, crystalline solid in 7.364 g (12.47 mmol, 97% yield). TLC R _f : 0.44 (50% EtOAc:Hexanes). ¹ H NMR (400 MHz, DMSO-d ₆ ): δ 11.63 (s, 3-NH, 1H), 8.41 (s, H-6, 1H), 7.79 (t, Tol, 4H), 7.22 (t, Tol, 4H), 6.22 (t, H-1’, 1H), 5.51 (m, H-3’, 1H), 4.55 (d, H-5’, 2H), 4.50 (m, H-4’, 1H), 2.64 (m, H-2’, 2H), 2.28 (s, Tol-CH ₃ , 3H), 2.25 (s, Tol-CH ₃ , 3H). ¹³ C NMR (101 MHz, DMSO-d ₆ ): δ 164.4, 164.1, 161.2, 149.5, 143.8, 143.2, 142.7, 129.5, 125.7, 84.8, 81.1, 72.0, 70.1, 63.9, 36.2, 20.6. MS calcd for C ₂₅ H ₂₃ IN ₂ O ₇ [M] ⁺ : 591.06, found: 591.1. [0073] (2S,3R,5S)-5-(4-amino-5-iodo-2-oxopyrimidin-1(2H)-yl)-2-(((4 - methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl 4-methylbenzoate (2b) To a suspension of 5-iodocytosine (7.913 g, 33.39 mmol, 1.3 eq) in dichloroethane, N,O- Bis(trimethylsilyl)acetamide (12.6 mL, 51.53 mmol, 2.0 eq) was added. The reaction mixture was heated to 85 °C and refluxed under nitrogen until a clear solution was obtained (ca. 30 minutes). The reaction mixture was cooled quickly to room temperature using an ice-water bath. Compound 1 (10.000 g, 25.72 mmol, 1.0 eq) was added and stirred at room temperature overnight. The reaction mixture was diluted with ethanol and allowed to stir for 10 minutes. The solvent was removed via rotary evaporation to yield the crude product 2b ((2S,3R,5S)-5-(4-amino-5-iodo-2-oxopyrimidin-1(2H)-yl)-2-((( 4- methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl 4-methylbenzoate) as an amber syrup. The purified product was obtained via flash chromatography (50% EtOAc:Hexanes) as an off-white, crystalline solid in 13.642 g (23.15 mmol, 90% yield). TLC R _f : 0.32 (50% EtOAc:Hexanes). ¹ H NMR (400 MHz, DMSO-d ₆ ): δ 8.98 (s, H-6, 1H), 7.81 (t, Tol, 4H), 7.61 (br s, 4-NH ₂ , 1H), 7.21 (t, Tol, 4H), 6.68 (br s, 4-NH ₂ , 1H), 6.17 (t, H-1’, 1H), 5.76 (m, H-3’, 1H), 4.49 (d, H-5’, 2H), 4.04 (m, H- 4’, 1H), 2.49 (m, H-2’, 2H), 2.26 (s, Tol-CH ₃ , 3H), 2.22 (s, Tol-CH ₃ , 3H). ¹³ C NMR (101 MHz, DMSO-d ₆ ): δ 164.8, 164.6, 161.6, 154.8, 149.3, 142.9, 142.6, 130.3, 126.4, 85.3, 82.8, 72.7, 70.5, 62.7, 38.1, 20.8. MS calcd for C ₂ [M + H] ⁺ : 590.08, found: 589.9. [0074] 5-(furan-2-yl)-1-((2S,4R,5S)-4-hydroxy-5-(hydroxymethyl)tetr ahydrofuran-2- yl)pyrimidine-2,4(1H,3H)-dione, CHK-01 (4a) Method A: To a solution of 2a (0.751 g, 1.27 mmol, 1.0 eq) and dichlorobis(triphenylphosphine)Pd(II) (0.090 g, 0.13 mmol, 0.1 eq) dissolved in a 6:1 solution of dioxanes (30.0 mL) and water (5.0 mL), furan-2-boronic acid (0.289 g, 2.58 mmol, 2.0 eq) and sodium carbonate (0.407 g, 3.84 mmol, 3.0 eq) were added. The reaction mixture was heated to 80 °C under nitrogen and allowed to stir for 4h. The reaction mixture was then cooled to rt and filtered over a celite pad. The TLC of the crude reaction mixture showed the product as a vibrant blue spot under UV light. Solvent was removed via rotary evaporation to afford the crude product 3a (2S,3R,5S)-5-(5-(furan-2-yl)-2,4-dioxo-3,4- dihydropyrimidin-1(2H)-yl)-2-(((4-methylbenzoyl)oxy)methyl)t etrahydrofuran-3-yl 4-methylbenzoate as a slightly yellow oil. Compound 3a was then used without further purification in the next step. TLC R _f : 0.65 (10% MeOH:DCM). Method B: In a 35-mL pressure vessel, 2a (0.258 g, 0.44 mmol, 1.0 eq) was dissolved in anhydrous 1,4- dioxanes (18.0 mL) and diH ₂ O (3.0 mL). To the vessel was also added furan-2-boronic acid (0.099 g, 0.88 mmol, 2.0 eq), PdCl ₂ (PPh ₃ ) ₂ (0.031 g, 0.04 mmol, 0.1 eq), and Na ₂ CO ₃ (0.141 g, 1.33 mmol, 3.0 eq). The pressure vessel was then flushed with Ar (g) for 5 minutes. Using a CEM Discover 2.0 Microwave Synthesizer, the reaction vessel was stirred for 3h at 90 °C. Afterwards, the crude reaction mixture was filtered over a celite pad with dichloromethane. The filtrate was then washed with saturated Na ₂ S ₂ O ₃ f remove drying agent. The TLC of the reaction mixture showed the product 3 as a vibrant blue spot under UV light. The solvent was removed via rotary evaporation to afford the crude product 3a as an amber oil and used without further purification in the next step. To a solution of 3a in 5% THF:MeOH, potassium carbonate (0.443 g, 3.21 mmol, 2.5 eq) was added. The reaction mixture was stirred at room temperature and monitored via TLC (10% MeOH:DCM) until completion. Solvent was removed via rotary evaporation, yielding the crude product as an amber oil. Purification via flash chromatography (10% MeOH:DCM) afforded the purified product CHK-01 as white solid in 0.341 g (1.16 mmol, 91% yield). TLC R _f : 0.38 (10% MeOH:DCM). ¹ H NMR (400 MHz, DMSO): δ 11.60 (s, 3-NH, 1H), 8.31 (s, H-6, 1H), 7.56 (s, H-5’’, 1H), 6.82 (s, H-3’’, 1H), 6.48 (m, H-4’’, 1H), 6.18 (t, H-1’, 1H), 5.33 (d, 3’-OH, 1H), 5.06 (t, 5’-OH, 1H), 4.22 (m, H-3’, 1H), 3.81 (m, H-4’, 1H), 3.58 (m, H-5’, 2H), 2.13 (t, H-2’, 2H) ^{MS calcd for C} _{13H14N2O6 [M + H]} ⁺ _{: 295.10, found: 295.0.} Elemental Analysis calcd for C ₁₃ H ₁₄ N ₂ O ₆ + 0.15 MeOH + 0.1 H ₂ O: C, 52.50; H, 4.96; N, 9.31. Found: C, 52.50; H, 4.93; N, 9.33. [0075] 1-((2S,4R,5S)-4-hydroxy-5-(hydroxymethyl)tetrahydrofuran-2-y l)-5-(thiophen-2- yl)pyrimidine-2,4(1H,3H)-dione, CHK-02 (4b) Method A: To a solution of 2a (0.507 g, 0.86 mmol, 1.0 eq) and dichlorobis(triphenylphosphine)Pd(II) (0.092 g, 0.13 mmol, 0.15 eq) dissolved in a 6:1 solution of dioxanes (30.0 mL) and water (5.0 mL), thiophene-2-boronic acid (0.223 g, 1.73 mmol, 2.0 eq) and sodium carbonate (0.274 g, 2.58 mmol, 3.0 eq) were added. The reaction mixture was heated to 80 °C under nitrogen and allowed to stir for 4h. The reaction mixture was then cooled to rt and filtered over a celite pad. The TLC of the crude reaction mixture showed the product as a vibrant blue spot under UV light. Solvent was removed via rotary evaporatio t ff d th d d t 3b (2S3R5S) 5 (24 di 5 (thi h 2 l) 34 dihydropyrimidin-1(2H)-yl)-2-(((4-methylbenzoyl)oxy)methyl)t etrahydrofuran-3-yl 4-methylbenzoate as an amber oil. Compound 3b was then used without further purification in the next step. TLC R _f : 0.67 (10% MeOH:DCM). Method B: In a 35-mL pressure vessel, 2a (0.250 g, 0.42 mmol, 1.0 eq) was dissolved in anhydrous 1,4- dioxanes (18.0 mL) and diH ₂ O (3.0 mL). To the vessel was also added thiophene-2-boronic acid (0.109 g, 0.85 mmol, 2.0 eq), PdCl ₂ (PPh ₃ ) ₂ (0.046 g, 0.06 mmol, 0.15 eq), and Na ₂ CO ₃ (0.137 g, 1.29 mmol, 3.0 eq). The pressure vessel was then flushed with Ar (g) for 5 minutes. Using a CEM Discover 2.0 Microwave Synthesizer, the reaction vessel was stirred for 3h at 90 °C. Afterwards, the crude reaction mixture was filtered over a celite pad with dichloromethane. The filtrate was then washed with saturated Na ₂ S ₂ O ₃ followed by brine. The combined organic phases were then dried over MgSO ₄ and filtered to remove drying agent. The TLC of the reaction mixture showed the product 3b as a vibrant blue spot under UV light. The solvent was removed via rotary evaporation to afford the crude product 3b as a dark amber oil and used without further purification in the next step. To a solution of 3b in 5% THF:MeOH, potassium carbonate (0.147 g, 1.07 mmol, 2.5 eq) was added. The reaction mixture was stirred at room temperature and monitored via TLC (15% MeOH:DCM) until completion. Solvent was removed via rotary evaporation, yielding the crude product as an amber oil. Purification via flash chromatography (15% MeOH:DCM) afforded the purified product CHK-02 as white solid in 0.114 g (0.37 mmol, 87% yield). TLC R _f : 0.52 (15% MeOH:DCM). ¹ H NMR (400 MHz, DMSO): δ 11.68 (s, 3-NH, 1H), 8.54 (s, H-6, 1H), 7.46 (d, H-5’’, 1H), 7.37 (d, H-3’’, 1H), 7.01 (t, H-4’’, 1H), 6.22 (t, H-1’, 1H), 5.31 (d, 3’-OH, 1H), 5.27 (d, 5’-OH, 1H), 4.25 (m, H-3’, 1H), 3.83 (m, H-4’, 1H), 3.63 (m, H-5’, 2H), 2.17 (m, H-2’, 2H) MS calcd for C ₁₃ H ₁₄ N ₂ O ₅ S [M + H] ⁺ : 311.07, found: 311.1. Elemental Analysis calcd for C ₁₃ H ₁₄ N ₂ O ₅ S + 0.3 H ₂ O: C, 49.45; H, 4.66; N, 8.87. Found: C, 49.33; H, 4.46; N, 8.79. [0076] 1-((2S,4R,5S)-4-hydroxy-5-(hydroxymethyl)tetrahydrofuran-2-y l)-5-(5-methylthiophen- 2-yl)pyrimidine-2,4(1H,3H)-dione, CHK-03 (4c) Method A: To a solution of 2a (0.500 g, 0.85 mmol, 1.0 eq) and dichlorobis(triphenylphosphine)Pd(II) (0.091, 0.13 mmol, 0.15 eq) dissolved in a 6:1 solution of dioxanes (30.0 mL) and water (5.0 mL), 5- methylthiophene-2-boronic acid (0.241 g, 1.70 mmol, 2.0 eq) and sodium carbonate (0.269 g, 2.54 mmol, 3.0 eq) were added. The reaction mixture was heated to 80 °C under nitrogen and allowed to stir for 4h. The reaction mixture was then cooled to rt and filtered over a celite pad. The TLC of the crude reaction mixture showed the product as a vibrant blue spot under UV light. Solvent was removed via rotary evaporation to afford the crude product 3 (((2S,3R,5S)-3-((4-methylbenzoyl)oxy)-5-(5-(5- methylthiophen-2-yl)-2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl )tetrahydrofuran-2-yl)methyl-4- methylbenzoate) as an amber oil. Compound 3c was then used without further purification in the next step. TLC R _f : 0.68 (10% MeOH:DCM). Method B: In a 35-mL pressure vessel, 2a (0.252 g, 0.42 mmol, 1.0 eq) was dissolved in anhydrous 1,4- dioxanes (18.0 mL) and diH ₂ O (3.0 mL). To the vessel was also added 5-methyl-thiophene-2-boronic acid (0.125 g, 0.85 mmol, 2.0 eq), PdCl ₂ (PPh ₃ ) ₂ (0.031 g, 0.04 mmol, 0.1 eq), and Na ₂ CO ₃ (0.135 g, 1.27 mmol, 3.0 eq). The pressure vessel was then flushed with Ar (g) for 5 minutes. Using a CEM Discover 2.0 Microwave Synthesizer, the reaction vessel was stirred for 3h at 90 °C. Afterwards, the crude reaction mixture was filtered over a celite pad with dichloromethane. The filtrate was then washed with saturated Na ₂ S ₂ O ₃ followed by brine. The combined organic phases were then dried over MgSO ₄ and filtered to remove drying agent. The TLC of the reaction mixture showed the product 3c as a vibrant blue spot under UV light. The solvent was removed via rotary evaporation to afford the crude product 3c as a dark brown oil and used without further purification in the next step. To a solution of 3c in 5% THF:MeOH, potassium carbonate (0.296 g, 2.14 mmol, 2.5 eq) was added. The reaction mixture was stirred at room temperature and monitored via TLC (15% MeOH:CHCl ₃ ) until completion. Solvent was removed via rotary evaporation, yielding the crude product as an amber oil. Purification via flash chromatography (15% MeOH:CHCl ₃ ) afforded the purified product CHK-03 (1-((2S,4R,5S)-4-hydroxy-5-(hydroxymethyl)tetrahydrofuran-2- yl)-5-(5-methylthiophen-2- yl)pyrimidine-2,4(1H,3H)-dione) as a pale yellow powder in 0.112 g (0.35 mmol, 42% yield). ^{TLC R} _{f: 0.48 (15% MeOH:CHCl3).} ¹ H NMR (400 MHz, DMSO-d ₆ ): δ 11.61 (s, 3-NH, 1H), 8.42 (s, H-6, 1H), 7.17 (d, H-3’’, 1H), 6.73 (d, H-4’’, 1H), 6.22 (t, H-1’, 1H), 5.30 (d, 3’-OH, 1H), 5.28 (d, 5’-OH, 1H), 4.29 (m, H-3’, 1H), 3.81 (m, H-4’, 1H), 3.65 (br s, H-5’, 2H), 2.38 (s, 5’’-Me, 3H), 2.20 (t, H-2’, 2H). ¹³ C NMR (101 MHz, DMSO-d ₆ ): δ 162.4, 149.1, 139.3, 134.7, 131.2, 123.6, 122.2, 107.3, 87.4, 84.6, 70.1, 61.6, 13.9. MS calcd for C ₁₄ H ₁₆ N ₂ O ₅ S [M + H] ⁺ : 325.09, found: 325.0. Elemental Analysis calcd for C ₁₄ H ₁₆ N ₂ O ₅ S + 0.05 MeOH + 0.45 H ₂ O: C, 52.07; H, 5.46; N, 7.66. Found: C, 52.34; H, 5.16; N, 7.39. [0077] 1-((2S,4R,5S)-4-hydroxy-5-(hydroxymethyl)tetrahydrofuran-2-y l)-5-(5-methylfuran-2- yl)pyrimidine-2,4(1H,3H)-dione, CHK-04 (4d) Method A: To a solution of 2a (0.502 g, 0.85 mmol, 1.0 eq) and dichlorobis(triphenylphosphine)Pd(II) (0.061 g, 0.09 mmol, 0.1 eq) dissolved in a 6:1 solution of dioxanes (30.0 mL) and water (5.0 mL), 5- methyl-furan-2-boronic acid (0.215 g, 1.71 mmol, 2.0 eq) and sodium carbonate (0.269 g, 2.55 mmol, 3.0 eq) were added. The reaction mixture was heated to 80 °C under nitrogen and allowed to stir for 4h. The reaction mixture was then cooled to rt and filtered over a celite pad. The TLC of the crude reaction mixture showed the product as a vibrant blue spot under UV light. Solvent was removed via rotary evaporation to afford the crude product 3d ((2S,3R,5S)-3-((4-methylbenzoyl)oxy)-5-(5-(5- methylfuran-2-yl)-2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)te trahydrofuran-2-yl)methyl 4- methylbenzoate as a pale yellow oil. Compound 3d was then used without further purification in the next step. TLC R _f : 0.68 (10% MeOH:DCM). Method B: In a 35-mL pressure vessel, 2a (0.251 g, 0.43 mmol, 1.0 eq) was dissolved in anhydrous 1,4- dioxanes (18.0 mL) and diH ₂ O (3.0 mL). To the vessel was also added 5-methyl-furan-2-boronic acid (0.108 g, 0.87 mmol, 2.0 eq), PdCl ₂ (PPh ₃ ) ₂ (0.033 g, 0.04 mmol, 0.1 eq), and Na ₂ CO ₃ (0.137 g, 1.27 mmol, 3.0 eq). The pressure vessel was then flushed with Ar (g) for 5 minutes. Using a CEM Discover 2.0 Microwave Synthesizer, the reaction vessel was stirred for 3h at 90 °C. Afterwards, the crude reaction m saturated Na ₂ S ₂ O ₃ followed by brine. The combined organic phases were then dried over MgSO ₄ and filtered to remove drying agent. The TLC of the reaction mixture showed the product 3d as a vibrant blue spot under UV light. The solvent was removed via rotary evaporation to afford the crude product 3d as an amber oil and used without further purification in the next step. To a solution of 3d in 5% THF:MeOH, potassium carbonate (0.294 g, 2.13 mmol, 2.5 eq) was added. The reaction mixture was stirred at room temperature and monitored via TLC (10% MeOH:DCM) until completion. Solvent was removed via rotary evaporation, yielding the crude product as an amber oil. Purification via flash chromatography (10% MeOH:DCM) afforded the purified product CHK-04 as an off-white solid in 0.207 g (0.67 mmol, 79% yield). TLC R _f : 0.39 (10% MeOH:DCM). ¹ H NMR (400 MHz, DMSO): δ 11.71 (s, 3-NH, 1H), 8.48 (s, H-6, 1H), 7.21 (d, H-3’’, 1H), 6.78 (d, H-4’’, 1H), 6.24 (t, H-1’, 1H), 5.32 (d, 3’-OH, 1H), 5.26 (d, 5’-OH, 1H), 4.31 (m, H-3’, 1H), 3.84 (m, H-4’, 1H), 3.67 (m, H-5’, 2H), 2.34 (s, 5’’-Me, 3H), 2.22 (m, H-2’, 2H) MS calcd for C ₁₄ H ₁₆ N ₂ O ₆ [M + H] ⁺ : 309.11, found: 309.0. Elemental Analysis calcd for C ₁₄ H ₁₆ N ₂ O ₆ + 0.6 H ₂ O: C, 52.70; H, 5.43; N, 8.78. Found: C, 52.52; H, 5.15; N, 8.70. [0078] 4-amino-5-(furan-2-yl)-1-((2S,4R,5S)-4-hydroxy-5-(hydroxymet hyl)tetrahydrofuran-2- yl)pyrimidin-2(1H)-one, CHK-05 (4e) Method A: Furan-2-boronic acid (0.286 g, 2.55 mmol, 2.0 eq) and sodium carbonate (4.03 g, 3.80 mmol, 3.0 eq) were added to a solution of 2b (0.751 g, 1.27 mmol, 1.0 eq) and dichlorobis(triphenylphosphine)Pd(II) (0.088 g, 0.13 mmol, 0.1 eq) dissolved in a 6:1 solution of dioxanes (30.0 mL) and water (5.0 mL). The reaction mixture was heated to 80 °C under nitrogen and allowed to stir for 4h. The reaction mixture was then cooled to room temperature and filtered over a celite pad. The TLC of the crude reaction mixture showed the product as a vibrant blue spot under UV light. The solvent was removed via rotary evaporation to afford the crude product 3e ((2S,3R,5S)-5-(4- amino-5-(furan-2-yl)-2-oxopyrimidin-1(2H)-yl)-2-(((4-methylb enzoyl)oxy)methyl)tetrahydrofuran-3- yl 4-methylbenzoate) as an amber oil and used without further purification in the next step. TLC R _f : 0.40 (10% MeOH:DCM). Method B: In a 35-mL pressure vessel, 2b (0.500 g, 0.85 mmol, 1.0 eq) was dissolved in anhydrous 1,4-dioxanes (18.0 mL) and diH ₂ O (3.0 mL). To the vessel was also added furan-2-boronic acid (0.191 g, 1.7 mmol, 2.0 eq), PdCl ₂ (PPh ₃ ) ₂ (0.060 g, 0.08 mmol, 0.1 eq), and Na ₂ CO ₃ (0.271 g, 2.54 mmol, 3.0 eq). The pressure vessel was then flushed with Ar (g) for 5 minutes. Using a CEM Discover 2.0 Microwave Synthesizer, the reaction vessel was stirred for 2h at 90 °C. Afterwards, the crude reaction mixture was filtered over a celite pad with dichloromethane. The filtrate was then washed with saturated Na ₂ S ₂ O ₃ followed by brine. The combined organic phases were then dried over MgSO ₄ and filtered to remove drying agent. The TLC of the reaction mixture showed the product 3e as a vibrant blue spot under UV light. The solvent was removed via rotary evaporation to afford the crude product as an amber oil and used without further purification in the next step. To a solution of 3e in 5% THF:MeOH potassium carbonate (0.442 g, 3.20 mmol, 2.5 eq) was added. The reaction mixture was stirred at room temperature and monitored via TLC (15% MeOH:CHCl ₃ ) until completion. Solvent was removed via rotary evaporation, yielding the crude product as an amber oil. Purification via flash chromatography (15% MeOH:CHCl ₃ ) followed by preparative TLC (15% MeOH:CHCl ₃ ) afforded the purified product CHK-05 (4-amino-5-(furan-2-yl)-1-((2S,4R,5S)-4- hydroxy-5-(hydroxymethyl)tetrahydrofuran-2-yl)pyrimidin-2(1H )-one) as a crystalline white solid in 0.172 g (0.59 mmol, 47% yield). TLC R _f : 0.35 (15% MeOH:CHCl ₃ ). ¹ H NMR (400 MHz, DMSO-d ₆ ): δ 8.22 (s, H-6, 1H) ,7.68 (m, H-5’’, 1H), 7.63 (br s, 4-NH ₂ , 1H), 6.65 (br s, 4NH ₂ , 1H), 6.54 (m, H-4” + H-3”, 2H), 6.13 (t, H-1’, 1H), 5.18 (t, 3’-OH, 1H), 5.04 (t, 5’-OH, 1H), 4.16 (m, H-3’, 1H), 3.77 (m, H-4’, 1H), 3.54 (m, H-5’, 2H), 2.15 (m, H-2’, 1H), 2.02 (m, H-2’, 1H). ¹³ C NMR (101 MHz, DMSO-d ₆ ): δ 162.6, 154.2, 147.6, 142.8, 140.6, 111.8, 107.5, 98.0, 87.7, 86.0, 70.7, 61.9, 39.8. MS calcd for C ₁₃ H ₁₅ N ₃ O ₅ [M + H] ⁺ : 294.11, found: 294.0. Elemental Analysis calcd for C ₁₃ H ₁₅ N ₃ O ₅ + 0.2 MeOH + 0.45 H ₂ O: C, 51.51; H, 5.47; N, 13.65. Found: C, 51.44; H, 5.27; N, 13.44. [0079] 4-amino-1-((2S,4R,5S)-4-hydroxy-5-(hydroxymethyl)tetrahydrof uran-2-yl)-5-(thiophen- 2-yl)pyrimidin-2(1H)-one, CHK-06 (4f) Method A: To a solution of 2b (0.506 g, 0.86 mmol, 1.0 eq) dissolved in a 6:1 solution of dioxanes (30.0 mL) and water (5.0 mL), was added dichlorobis(triphenylphosphine)Pd(II) (0.092 g, 0.13 mmol, 0.15 eq). Thiophene-2-boronic acid (0.223 g, 1.74 mmol, 2.0 eq) and sodium carbonate (0.274, 2.58 mmol, 3.0 eq) were then added to the reaction mixture. The reaction mixture was heated to 80 °C under nitrogen and allowed to stir for 4h. The reaction mixture was then cooled to room temperature and filtered over a celite pad. The TLC of the crude reaction mixture showed the product as a vibrant blue spot under UV light. The solvent was removed via rotary evaporation to afford the crude product 3f (2S,3R,5S)-5-(4-amino-2-oxo-5-(thiophen-2-yl)pyrimidin-1(2H) -yl)-2-(((4- methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl 4-methylbenzoate) as an amber oil and used without ^{further purification in the next step. TLC R} _{f: 0.41 (10% MeOH:DCM).} Method B: In a 35-mL pressure vessel, 2b (0.250 g, 0.42 mmol, 1.0 eq) was dissolved in anhydrous 1,4-dioxanes (18.0 mL) and diH ₂ O (3.0 mL). To the vessel was also added thiophene-2-boronic acid (0.110 g, 0.86 mmol, 2.0 eq), PdCl2(PPh3)2 (0.046 g, 0.06 mmol, 0.15 eq), and Na2CO3 (0.136 g, 1.29 mmol, 3.0 eq). The pressure vessel was then flushed with Ar (g) for 5 minutes. Using a CEM Discover 2.0 Microwave Synthesizer, the reaction vessel was stirred for 2h at 90 °C. Afterwards, the crude reaction mixture was filtered over a celite pad with dichloromethane. The filtrate was then washed with saturated Na ₂ S ₂ O ₃ followed by brine. The combined organic phases were then dried over MgSO ₄ and filtered to remove drying agent. The TLC of the reaction mixture showed the product 3f as a vibrant blue spot under UV light. The solvent was removed via rotary evaporation to afford the crude product 3f as an amber oil and used without further purification in the next step. To a solution of 3f in 5% THF:MeOH potassium carbonate (0.301 g, 2.16 mmol, 2.5 eq) was added. The reaction mixture was stirred at room temperature and monitored via TLC (15% MeOH:CHCl ₃ ) until completion. Solvent was removed via rotary evaporation, yielding the crude product as a dark amber oil. Purification via flash chromatography (15% MeOH:CHCl ₃ ) afforded the purified product CHK-06 as a pale yellow solid in 0.101 g (0.33 mmol, 38% yield). TLC R _f : 0.39 (15% MeOH:CHCl ₃ ). ¹ H NMR (400 MHz, DMSO): δ 8.19 (s, H-6, 1H) ,7.66 (m, H-5’’, 1H), 7.57 (br s, 4-NH ₂ , 1H), 6.61 (br s, 4NH ₂ , 1H), 6.48 (m, H-4” + H-3”, 2H), 6.05 (t, H-1’, 1H), 5.16 (t, 3’-OH, 1H), 4.98 (t, 5’-OH, 1H), 4.14 (m, H-3’, 1H), 3.72 (m, H-4’, 1H), 3.54 (m, H-5’, 2H), 2.13 (m, H-2’, 1H), 2.06 (m, H-2’, 1H) MS calcd for C ₁₃ H ₁₅ N ₃ O ₄ S [M + H] ⁺ : 310.09, found: 310.0. Elemental Analysis calcd for C ₁₃ H ₁₅ N ₃ O ₄ S + 0.05 H ₂ O: C, 50.33; H, 4.91; N, 13.54. Found: C, 50.18; H, 4.72; N, 13.49. [0080] 4-amino-1-((2S,4R,5S)-4-hydroxy-5-(hydroxymethyl)tetrahydrof uran-2-yl)-5-(5- methylthiophen-2-yl)pyrimidin-2(1H)-one, CHK-07 (4g) Method A: To a solution of 2b (0.258 g, 0.44 mmol, 1.0 eq) dissolved in a 6:1 solution of dioxanes (30.0 mL) and water (5.0 mL), was added dichlorobis(triphenylphosphine)Pd(II) (0.045 g, 0.07 mmol, 0.15 eq).5-Methyl-thiophene-2-boronic acid (0.126 g, 0.89 mmol, 2.0 eq) and sodium carbonate (0.142, 1.32 mmol, 3.0 eq) were then added to the reaction mixture. The reaction mixture was heated to 80 °C under nitrogen and allowed to stir for 4h. The reaction mixture was then cooled to room temperature and filtered over a celite pad. The TLC of the crude reaction mixture showed the product as a vibrant blue spot under UV light. The solvent was removed via rotary evaporation to afford the crude product 3g ((2S,3R,5S)-5-(4-amino-5-(5-methylthiophen-2-yl)-2-oxopyrimi din-1(2H)-yl)-2-(((4- methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl 4-methylbenzoate) as an amber oil and used without further purification in the next step. TLC R _f : 0.49 (10% MeOH:DCM). To a solution of 3g in 5% THF:MeOH potassium carbonate (0.152 g, 1.10 mmol, 2.5 eq) was added. The reaction mixture was stirred at room temperature and monitored via TLC (15% MeOH:CHCl ₃ ) until completion. Solvent was removed via rotary evaporation, yielding the crude product as a dark amber oil. Purification via flash chromatography (15% MeOH:CHCl ₃ ) afforded the purified product CHK-07 as a yellow solid in 0.048 g (0.14 mmol, 33% yield). TLC R _f : 0.43 (15% MeOH:CHCl ₃ ). ¹ H NMR (400 MHz, DMSO): δ 8.14 (s, H-6, 1H), 7.52 (br s, 4-NH ₂ , 1H), 6.56 (br s, 4-NH ₂ , 1H), 6.33 (m, H-4” + H-3”, 2H), 6.12 (m, H-1’, 1H), 5.14 (t, 3’-OH, 1H), 5.05 (t, 5’-OH, 1H), 4.12 (m, H-3’, 1H), 3.74 (m, H-4’, 1H), 3.53 (m, H-5’, 2H), 2.24 (s, 5’’-Me), 2.11 (m, H-2’, 1H), 2.07 (m, H-2’, 1H) MS calcd for C ₁₄ H ₁₇ N ₃ O ₄ S [M + H] ⁺ : 324.10, found: 324.0. Elemental Analysis calcd for C ₁₄ H ₁₇ N ₃ O ₄ S + 0.5 MeOH + 0.15 H ₂ O: C, 50.91; H, 5.69; N, 12.28. Found: C, 50.68; H, 5.42; N, 12.01. [0081] 4-amino-1-((2S,4R,5S)-4-hydroxy-5-(hydroxymethyl)tetrahydrof uran-2-yl)-5-(5- methylfuran-2-yl)pyrimidin-2(1H)-one, CHK-08 (4h) Method A: To a solution of 2b (0.251 g, 0.43 mmol, 1.0 eq) dissolved in a 6:1 solution of dioxanes (30.0 mL) and water (5.0 mL), was added dichlorobis(triphenylphosphine)Pd(II) (0.030 g, 0.04 mmol, 0.1 eq).5-Methyl-furan-2-boronic acid (0.111 g, 0.87 mmol, 2.0 eq) and sodium carbonate (0.135, 1.28 mmol, 3.0 eq) were then added to the reaction mixture. The reaction mixture was heated to 80 °C under nitrogen and allowed to stir for 4h. The reaction mixture was then cooled to room temperature and filtered over a celite pad. The TLC of the crude reaction mixture showed the product as a vibrant blue spot under UV light. The solvent was removed via rotary evaporation to afford the crude product 3h ((2S,3R,5S)-5-(4-amino-5-(5-methylfuran-2-yl)-2-oxopyrimidin -1(2H)-yl)-2-(((4- methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl 4-methylbenzoate) as an yellow oil and used without further purification in the next step. TLC R _f : 0.49 (10% MeOH:DCM). To a solution of 3h in 5% THF:MeOH potassium carbonate (0.148 g, 1.07 mmol, 2.5 eq) was added. The reaction mixture was stirred at room temperature and monitored via TLC (15% MeOH:CHCl ₃ ) until completion. Solvent was removed via rotary evaporation, yielding the crude product as an amber oil. Purification via flash chromatography (15% MeOH:CHCl ₃ ) afforded the purified product CHK-08 as an off-white solid in 0.038 g (0.12 mmol, 29% yield). TLC R _f : 0.42 (15% MeOH:CHCl ₃ ). ¹ H NMR (400 MHz, DMSO): δ 8.17 (s, H-6, 1H), 7.57 (br s, 4-NH ₂ , 1H), 6.59 (br s, 4-NH ₂ , 1H), 6.38 (m, H-4” + H-3”, 2H), 6.10 (m, H-1’, 1H), 5.17 (t, 3’-OH, 1H), 5.02 (t, 5’-OH, 1H), 4.18 (m, H-3’, 1H), 3.76 (m, H-4’, 1H), 3.57 (m, H-5’, 2H), 2.26 (s, 5’’-Me), 2.15 (m, H-2’, 1H), 2.03 (m, H-2’, 1H) MS calcd for C ₁₄ H ₁₇ N ₃ O ₅ [M + H] ⁺ : 308.13, found: 308.1. Elemental Analysis calcd for C ₁₄ H ₁₇ N ₃ O ₅ + 0.45 MeOH + 0.05 H ₂ O: C, 53.43; H, 5.84; N, 12.89. Found: C, 53.49; H, 5.76; N, 12.79. EXAMPLE 4 [0082] Below is an embodiment of a method of making the CHK-50 compound. [0083] 4-amino-5-bromo-1-((2R,5S)-2-(hydroxymethyl)-1,3-oxathiolan- 5-yl)pyrimidin-2(1H)- one (compound 2) In a round bottom flask, 3TC (5.002g, 21.8 mmol, 1.0 eq) was dissolved in anhydrous pyridine (60.0 mL). The solution was cooled to 0°C in an ice bath. A 5% w/w solution of Br ₂ (1.23 mL, 24.0 mmol, 1.1 eq) in anhydrous tetrachloromethane (48.2 mL) was slowly added to the reaction mixture dropwise at 0°C under Ar(g) while stirring. The reaction was then gradually warmed to rt and stirred under inert atmosphere for 24h to afford an opaque yellow solution. To this, was added Na ₂ CO ₃ (1.158 g, 11.2 mmol, 0.5 eq) and the reaction mixture was stirred for 1h. The majority of the pyridine solvent was then removed via rotary evaporation, followed by co-evaporation with toluene (3 x 25 mL). Purification via flash chromatography (10% MeOH:DCM) afforded the purified product 2 (4-amino-5-bromo-1- ((2R,5S)-2-(hydroxymethyl)-1,3-oxathiolan-5-yl)pyrimidin-2(1 H)-one) as a white solid in 0.851 g (2.76 mmol, 13% yield). ¹ H NMR (400 MHz, DMSO): δ 8.19 (s, 1H), 7.79 (br s, 1H, NH), 6.92 (br s, 1H, NH), 6.11 (dd, 1H), 5.34 (br t, 1H, OH), 5.12 (t, 1H), 3.76 (dt, 1H), 3.65 (dt, 1h), 3.29 (dd, 1H), 3.12 (dd, 1H). ¹³ C NMR (101 MHz, DMSO): δ 162.0, 153.4, 142.2, 87.2, 86.6, 86.0, 61.7, 37.4. [0084] 4-amino-5-(furan-2-yl)-1-((2R,5S)-2-(hydroxymethyl)-1,3-oxat hiolan-5-yl)pyrimidin- 2(1H)-one, CHK-50 In a round bottom flask, 2 (0.445 g, 1.44 mmol, 1.0 eq) was dissolved in a 6:1 solution of anhydrous 1,4-dioxanes (30.0 mL) and water (5.0 mL). Furan-2-boronic acid (0.325 g, 2.89 mmol, 2.0 eq), Na ₂ CO ₃ (0.458 g, 4.33 mmol, 3.0 eq), and PdCl ₂ (PPh ₃ ) ₂ (0.103 g, 0.14 mmol, 0.1 eq) were then added to the reaction flask. The reaction was then heated to 80°C under Ar (g) and allowed to stir for 12 h. The reaction mixture was then cooled to room temperature and filtered over a celite pad. The filtrate was then washed with Na ₂ S ₂ O ₃ followed by a wash with NaHCO ₃ (100 mL) then extraction with DCM (2 x 100 mL). The combined organic layers were then washed with brine (100 mL) and dried over MgSO ₄ . The drying agent was removed via filtration. Solvent was removed via rotary evaporation to afford the crude product as a tan residue. Purification via flash chromatography (10% MeOH:DCM) afforded the purified product CHK-50 (4-amino-5-(furan-2-yl)-1-((2R,5S)-2-(hydroxymethyl)-1,3-oxa thiolan-5- yl)pyrimidin-2(1H)-one) as a pale yellow solid in 0.081 g (0.27 mmol, 19% yield). ¹ H NMR (400 MHz, DMSO): δ 8.29 (s, 1H), 7.66 (br s, 1H, NH), 6.70 (br s, 1H, NH), 6.58 (s, 1H), 6.53 (s, 1H), 6.22 (t, 1H), 5.42 (br t, 1H, OH), 5.19 (t, 1H), 3.74 (dt, 1H), 3.46 (dt, 1h), 3.29 (dd, 1H), 3.12 (dd, 1H). MS calcd for C ₁₂ H ₁₃ N ₃ O ₄ S [M + H] ⁺ : 296.07, found: 296.1. Elemental Analysis calcd for C ₁₂ H ₁₃ N ₃ O ₄ S + 0.15 MeOH + 0.1 H ₂ O: C, 48.34; H, 4.61; N, 13.92. Found: C, 48.33; H, 4.45; N, 13.76. EXAMPLE 5 Testing Methods and Results Primary CPE test method (USU). [0085] Four-concentration CPE inhibition assays are performed on confluent or near-confluent cell culture monolayers in 96-well plates. Cells are maintained in MEM or DMEM supplemented with FBS as required for each cell line. For antiviral assays the same medium is used but with FBS at 2% or less and supplemented with 50 µg/ml gentamicin (10 µg/mL EDTA and 1 IU/mL trypsin are added for ^{influenza, and 25 mM MgCl} _{2 for rhinovirus and enterovirus-D68). The test compound is prepared for} testing at 4-concentrations, usually 100, 10, 1.0, and 0.1 µg/ml or µM. Higher or lower concentrations are used at the direction of the sponsor/COR. Five microwells are used per dilution: three for infected wells and two for uninfected toxicity evaluation wells that are run in parallel. Controls for the experiment consist of six microwells that are infected but not treated (virus controls) and six that are untreated (cell controls). The virus control and cell control wells are on every 96-well test plate. A known active drug is tested in parallel with each assay run as a positive control, using the same method as is used for test compounds. [0086] Growth medium is removed from the 96-well plates of cells, then the test compound is applied in 0.1 ml volume to wells at 2x concentration. Virus, normally <10050% cell culture infectious doses (CCID ₅₀ ) in 0.1 ml volume, is added to wells designated for virus infection. Medium devoid of virus is placed in enterovirus-D68) with 5% CO ₂ until maximum CPE is observed microscopically in virus control wells. Plates are then stained with 0.011% neutral red for approximately two hours at 37 ^o C with 5% CO ₂ . The neutral red medium is removed by complete aspiration, and the cells rinsed with phosphate buffered saline (PBS) to remove residual dye. The PBS is completely removed, and the incorporated neutral red is eluted with 50% Sorensen’s citrate buffer/50% ethanol for at least 30 minutes. Neutral red dye penetrates living cells, thus, the more intense the red color, the larger the number of viable cells present. The dye content in each well is quantified by optical density (OD) on a spectrophotometer at 540 nm wavelength. The OD for each set of wells is converted to a percentage compared to untreated control wells using a Microsoft Excel™ computer-based spreadsheet. Infected wells are normalized to the virus control. The 50% effective (EC ₅₀ , virus-inhibitory) concentrations and 50% cytotoxic (CC ₅₀ , cell- inhibitory) concentrations are then calculated by regression analysis. The quotient of CC ₅₀ divided by EC ₅₀ gives the selectivity index (SI ₅₀ ) value. The percent CPE in each well may also be read microscopically, calculated as above, and reported as a second data set from the same plate for verification. [0087] Compounds showing SI ₅₀ values ≥10 are considered active and merit further investigation at the discretion of the COR. For certain viruses that are difficult to inhibit, such as West Nile virus, compounds with SI ₅₀ values ≥5 may be considered for further testing as well. One set of data is provided to NIH for each compound tested and includes EC ₅₀ , CC ₅₀ , and SI ₅₀ obtained from the neutral red assay. For fastidious viruses that don’t cause observable CPE (e.g., LCMV, Heartland, and SFTS), the cell lysate can be harvested and titrated as described in the secondary assay below. An EC ₉₀ is then reported instead of an EC ₅₀ value, and visual readings are used to determine the toxicity (CC ₅₀ ). Secondary assay method: CPE and virus yield reduction (VYR) test (USU). [0088] Active compounds are submitted for secondary assays at the discretion of the COR. The secondary assay confirms the CPE assay result, with the principal assessment being virus yield reduction (VYR). It employs a similar method as described for the primary assay in section 2C.8.1, with the differences noted in this section. The secondary assay is run independently of the primary test with cells, culture media, infectious virus solution, and test compound dilutions all newly prepared for this assay. Eight half-log ₁₀ concentrations are tested for antiviral activity and cytotoxicity. After sufficient virus replication occurs (normally 3 days post infection), a sample of supernatant is taken from each infected well (three replicate wells are pooled) and titrated immediately (as with RSV) or frozen and stored for virus titration at a later time. Alternately, a separate plate may be prepared, and the plate may be frozen and then thawed to release intracellular or cell-associated virus to test the cell lysate rather than supernatant fluid. After maximum CPE is observed, the plates are stained with neutral red dye as described above to generate the neutral red EC ₅₀ , CC ₅₀ , and SI ₅₀ values. Uninfected wells are tested in parallel for compound toxicity as in the primary assay explained above. The positive control compound is evaluated in parallel with each test. [0089] The second step is to determine the virus titer in the supernatant or lysate samples. Samples from triplicate wells, collected as described above, are pooled and tested by endpoint dilution. This is a direct determination virus produced in the presence of the test compound compared to virus from untreated, infected controls. This is accomplished by making log ₁₀ dilutions of the pooled samples and plating each dilution on 3 or 4 microwells with fresh monolayers of cells in 96-well plates. Plates are incubated until maximum CPE is observed, then each well is scored for presence (+) or absence (-) of virus and the virus titer calculated using the Reed-Meunch method (1938). Plotting the log of the inhibitor concentration versus log ₁₀ of virus produced at each concentration allows calculation of the 90% (one log ₁₀ reduction) effective concentration by linear regression. Dividing CC ₅₀ toxicity obtained in the CPE assay by the EC ₉₀ gives the SI ₉₀ value (so named because it is derived from a 90% virus- inhibitory value). Two sets of data are provided to NIH: (1) EC ₅₀ , CC ₅₀ , and SI ₅₀ obtained from the neutral red assay, and (2) EC ₉₀ obtained from the VYR assay, CC ₅₀ , and SI ₉₀ . For fastidious viruses that do not cause notable CPE, the EC ₉₀ and CC ₅₀ will be reported, but no EC ₅₀ value. Primary plaque reduction assay method for BSL-4 viruses (Lassa fever, Ebola, Marburg, and Nipah). [0090] Confluent or near-confluent cell culture monolayers in 12-well disposable cell culture plates are prepared.24- or 48- well plates could be used for EBOV and MARV as well. Cells are maintained in MEM supplemented with 5 to 10% FBS. The test compound is prepared at four log ₁₀ final concentrations, usually 100, 10, 1.0, and 0.1 μg/ml or μM (depending upon the sponsor’s preference) in 2X MEM. Lower concentrations are used when insufficient compound is provided, after discussion with the PI and COR. The virus control and cell control are run in parallel with each tested compound. Further, a known active drug is tested as a positive control drug (e.g., favipiravir) using the same experimental set-up as described for the virus and cell control. The positive control is tested with each test run. Test compounds and positive controls are typically tested in biological triplicates. The assay is initiated by first removing growth media from the 12-well plates of cells, and infecting cells with 0.01 MOI of virus or about 50 to 100 plaque forming units (pfu). Cells are incubated for 60 min: 100μl inoculum/ well, at 37°C, 5% CO ₂ with constant gentle rocking. Virus inoculum is removed, cells washed and overlaid with either 1% agarose, 1.8% Tragacanth, or 1% methylcellulose diluted 1:1 with 2x MEM and supplemented with 2 to 5% FBS, 1% penicillin/streptomycin, and with the corresponding drug concentration. Cells are incubated at 37 ⁰ C with 5% CO ₂ for 5 (Lassa fever), 10-12 (Ebola, Marburg), or 2-3 (Nipah) days. The overlay is then removed, and plates stained with 0.05% crystal violet in 10% buffered formalin for approximately twenty minutes at room temperature. The plates are then washed, dried, and the number of plaques counted. The number of plaques in each set of compound dilution is converted to a percentage relative to the untreated virus control. The 50% effective (EC ₅₀ , virus-inhibitory) concentrations are then calculated by linear regression analysis. Cytotoxicity is evaluated in parallel to the actual primary PR assay. [0091] The cytotoxicity assay (In vitro Toxicology Assay Kit, Neutral red based; Sigma) is being performed in 96-well plates following the manufacturer’s instructions. Briefly, growth medium is removed from confluent cell monolayers and replaced with fresh medium (total of 100µl) containing the test compound with the concentrations as indicated for the primary assay. Control wells will contain medium with the positive control or medium devoid of compound. Wells without cells and growth medium only serve as blanks. A total of up to five replicates are performed for each condition. Plates are then incubated for 2 to 12 days (depending on the virus used) at 37ºC with 5% CO ₂ . The plates are then stained with 0.033% neutral red for approximately two hours at 37 ^o C in a 5% CO ₂ incubator. The neutral red medium is removed by complete aspiration, and the cells rinsed with phosphate buffered saline (PBS) to remove residual dye. The PBS is completely removed, and the incorporated neutral red is eluted with 1% acetic acid/50% ethanol for at least 10 minutes. Neutral red dye penetrates into living cells, thus, the more intense the red color, the more viable cells are present in the wells. The dye content in each well is quantified using a 96-well spectrophotometer at 540 nm wavelength and 690 nm wavelength (background reading). The 50% cytotoxic (CC ₅₀ , cell-inhibitory) concentrations are then calculated by linear regression analysis. In addition, cytotoxic effects may be visually evaluated in infected cell monolayers of the plaque assay test, and these may be used to calculate the CC50 value when this is more applicable. The quotient of CC ₅₀ divided by EC ₅₀ gives the selectivity index (SI ₅₀ ) value. The positive control compound is evaluated in parallel in each test. One set of data is provided to NIH for each compound tested: EC ₅₀ , CC ₅₀ , and SI ₅₀ obtained from the plaque reduction assay. Secondary VYR assay for BSL-4 viruses (Lassa fever, Ebola, Marburg, and Nipah). [0092] The secondary assay involves similar methodology to what is described in the previous paragraphs using 12, 24, or 48-well plates of cells. The differences are noted in this section. The secondary assay is run independently of the primary test by using fresh cells, fresh culture medium, freshly prepared virus (from frozen stock), and newly prepared compound dilutions. The test compound is prepared at eight half-log ₁₀ final concentrations, usually 100, 32, 10, 3.2, 0.1, and 0.032 µg/ml or µM (depending upon the sponsor’s preference). Lower concentrations are used when insufficient compound is provided upon approval of the PI. Test compound is applied in 0.2 to 1 ml (depending on the plate type used) of total volume. Tissue culture supernatant (TCS) aliquots are collected at appropriate time points and then be used to determine the compounds inhibitory effect on virus replication. Virus that was replicated in the presence of test compound is titrated and compared to virus from untreated, infected controls. For titration of TCS, serial ten-fold dilutions are prepared and used to infect fresh monolayers of cells. Cells are overlaid with overlay media as described in the previous section and the number of plaques is determined. Test compounds and positive controls are typically tested in biological triplicates untreated virus control. Plotting the log ₁₀ of the inhibitor concentration versus log virus titer or percentage of virus produced at each concentration allows calculation of the 90% (one log ₁₀ ) effective concentration by linear regression. Cytotoxicity is determined in uninfected cells as described in the previous section, and 50% cytotoxic (CC ₅₀ ). One set of data is provided to NIH for each compound tested: EC ₉₀ , CC ₅₀ , and SI ₉₀ obtained from the virus yield reduction assay. The positive control compound is evaluated in parallel in each test. Antiviral Materials and Methods Cell culture and virus strains. [0093] Human foreskin fibroblast (HFF) cells prepared from human foreskin tissue were obtained from the University of Alabama at Birmingham tissue procurement facility with approval from its IRB. The tissue was incubated at 4°C for 4 h in Clinical Medium consisting of minimum essential media (MEM) with Earl’s salts supplemented with 10% fetal bovine serum (FBS) (Hyclone, Inc. Logan UT), L- glutamine, fungizone, and vancomycin. Tissue is then placed in phosphate buffered saline (PBS), minced, rinsed to remove the red blood cells, and resuspended in trypsin/EDTA solution. The tissue suspension is incubated at 37°C and gently agitated to disperse the cells, which are collected by ^{centrifugation. Cells are resuspended in 4 ml Clinical Medium and placed in a 25 cm2} _{flask and} incubated at 37°C in a humidified CO ₂ incubator for 24 h. The media is then replaced with fresh Clinical Medium, and the cell growth is monitored daily until a confluent monolayer has formed. The HFF cells are then expanded through serial passages in standard growth medium of MEM with Earl’s salts supplemented with 10% FBS, L-glutamine, penicillin, and gentamycin. The cells are passaged routinely and used for assays at or below passage 10 (1,2). COS7, C-33 A, Guinea Pig Lung, and Mouse embryo fibroblast cells were obtained from ATCC and maintained in standard growth medium of MEM with Earl’s salts supplemented with 10% FBS, L-glutamine, penicillin, and gentamycin. [0094] Akata cells were kindly provided by John Sixbey (Louisiana State University, Baton Rouge, LA). BCBL-1 cells were obtained through the NIH AIDS Research and Reference Reagent Program, Division of AIDS, NIAID, NIH. Molt-3 cells were obtained from Scott Schmid at the Centers for Disease Control and Prevention, Atlanta, GA. Lymphocytes are maintained routinely in RPMI 1640 (Mediatech, Inc., Herndon, VA) with 10% FBS, L-glutamine and antibiotics and passaged twice a week, as described previously (Keith et al., 2018; Prichard et al., 2011). [0095] The E-377 strain of HSV-1 (herpes simplex virus-1) was a gift of Jack Hill (Burroughs Wellcome). The HCMV strain AD169, HSV-2 strain G (herpes simplex virus-2), AdV5 strain Adenoid 75, GPCMV strain 22122 and MCMV (cytomegalovirus) strain Smith were obtained from the American Type Culture Collection (ATCC, Manassas, VA). The Copenhagen strain of VACV (vaccinia virus) and Brighton strain, CPXV (Cowpox Virus) were kindly provided by John W. Huggins (Department of Viral The Disease). VZV (varicella zoster virus), strain Ellen, the polyomavirus BK virus Gardner strain (BKV) and JC virus (JCV) MAD4 strain were obtained from the ATCC. Akata cells latently infected with EBV were obtained from John Sixbey. The Z29 strain of HHV-6B (human herpesvirus) was a gift of Scott Schmid at the Centers for Disease Control and Prevention, Atlanta GA. HHV-8 (human herpesvirus) was obtained as latently infected BCBL-1 cells through the NIH AIDS Research and Reference Reagent Program. Antiviral Assays. [0096] Each experiment that evaluates the antiviral activity of the compounds includes both positive and negative control compounds to ensure the performance of each assay. Concurrent assessment of cytotoxicity is also performed for each study in the same cell line and with the same compound exposure (see below). i. CPE assays for HSV-1, HSV-2, VZV, HCMV (Human cytomegalovirus), MCMV (Murine cytomegalovirus), GPCMV (Guinea Pig cytomegalovirus), AdV (Adenovirus), VACV, CPXV. Assays were performed in monolayers as described (Hartline et al., 2018). Briefly, cells were seeded in 384 well plates and incubated for 24h to allow the formation of confluent monolayers. Dilutions of test drug were prepared directly in the plates and the monolayers infected at a predetermined MOI based on virus used. After incubation, cytopathology was determined by the addition of CellTiter-Glo (CTG) reagent. Concentrations of test compound sufficient to reduce CPE by 50% (EC ₅₀ ) or decrease cell viability by 50% (CC ₅₀ ) were interpolated using standard methods in Microsoft Excel. For MCMV, the assays were run in 96 well plates in mouse embryo fibroblast cells, with drug dilutions performed as above. After a 7 d incubation, DNA was extracted and a qPCR was run to calculate drug efficacy using primers 5’-TCA GCC ATC AAC TCT GCT ACC AAC-3’ (SEQ ID NO: 1) , 5’-ATC TGA AAC AGC CGT ATA TCA TCT TG- 3’ (SEQ ID NO: (SEQ ID NO: 2), and probe 5’-TTC TCT GTC AGC TAG CCA ATG ATA TCT TCG AGC-3’(SEQ ID NO: 3). Toxicity was measured using CTG as above. For GPCMV, the assays were run in 384 well plates in Guinea Pig Lung cells, with drug dilutions performed as above. After a 7 d incubation, DNA was extracted and a qPCR was run to calculate drug efficacy using primers 5’-GAGGTCGAGAAGCTGATATTGG-3’ (SEQ ID NO: 4), 5’- GTCTCTTCCTATGCGGGTTATC -3’(SEQ ID NO: 5), and probe 5’- ACGTCACTTTGAGGGCCAACTGAT-3’ (SEQ ID NO: 6). Toxicity was measured using CTG as above. ii. Plaque reduction assays for HSV-1, HSV-2, VZV, VACV, CPXV. Monolayers of HFF cells we confluency. Media was then aspirated from the wells and 0.2 ml of virus was added to each of three wells to yield 20-30 plaques in each well. The virus was allowed to adsorb to the cells for 1 h and the plates were agitated every 15 minutes. Compounds were diluted in assay media consisting of MEM with Earl’s salts supplemented with 2% FBS, L-glutamine, penicillin, and gentamycin. Diluted drug was added to duplicate wells and the plates were incubated for various times, depending on the virus used. For VACV and CPXV, dilutions of 2X drug was added to an equal volume of 1% agarose. For HSV-1 and -2, the monolayers were then stained with 1% crystal violet in 20% methanol and the unbound dye removed by washing with dH ₂ 0. For all other assays, the cell monolayer was stained with 1% Neutral Red solution for 4 - 6h then the stain was aspirated, and the cells were washed with PBS. For all assays, plaques were enumerated using a stereomicroscope and the concentration of compound that reduced plaque formation by 50% (EC ₅₀ ) was interpolated from the experimental data. iii. Yield reduction assays for HSV-1, HSV-2, HCMV, VACV, CPXV and AdV. Monolayers of HFF cells were prepared in 96-well plates and incubated at 37°C for 1 d to allow the cells to reach confluency. Media was then aspirated from the wells and cells infected at a high MOI. At 1 h following infection, the inocula were removed and the monolayers rinsed with fresh media. Compounds were then diluted in assay media consisting of MEM with Earl’s salts supplemented w ^{ith 2% FBS,} _{L-glutamine, penicillin, and gentamycin. Drug dilutions were added to the wells} and the plates were incubated for various times, depending on the virus used and represents a single replication cycle for the virus. A duplicate set of dilutions were also performed but remained uninfected to serve as a cytotoxicity control and received equal compound exposure. Supernatants from each of the infected wells were subsequently titered using CTG in a TCID ₅₀ assay to quantify the progeny virus. For HCMV only, viral yield in the supernatants from the infected cells were titered using qPCR with HCMV primers 5’- AGG TCT TCA AGG AAC TCA GCA AGA-3’ (SEQ ID NO: 7), 5’-CGG CAA TCG GTT TGT TGT AAA-3’(SEQ ID NO: 8), and probe 5’-CCG TCA GCC ATT CTC TCG GC-3’(SEQ ID NO: 9). For cytotoxicity controls, cytotoxicity was assessed using CTG according to the manufacturer’s suggested protocol. For all assays, the concentration of compound that reduced virus titer by 90% (EC ₉₀ ) was interpolated from the experimental data. iv. Secondary Assay for GPCMV. Compounds that were positive in the CPE assay were confirmed in a similar assay in 96-well plates according to established laboratory protocols with the compounds added 1h post infection to identify compounds that inhibit early stages of replication including adsorption and penetration. Genome copy number was determined by qPCR using primers 5’-GAG GTC GAG AAG CTG ATA TTG G-3’ (SEQ ID NO: 10), 5’-GTC TCT TCC TAT GCG GGT TAT C-3’ (SEQ ID NO: 11), and probe 5’-ACG TCA CTT TGA GG v. Secondary assay for MCMV. Compounds that were positive in the CPE assay were confirmed in a similar assay in 96-well plates according to established laboratory protocols with the compounds added 1h post infection to identify compounds that inhibit early stages of replication including adsorption and penetration. Additionally, 121:3 dilutions were done instead of 61:5 dilutions for added accuracy. Genome copy number was determined by qPCR using primers 5’- TCAGCCATCAACTCTGCTACCAAC-3’ (SEQ ID NO: 13), 5’ ATCTGAAACAGCCGTATATCATCTTG-3’ (SEQ ID NO: 14), and probe 5’- TTCTCTGTCAGCTAGCCAATGATATCTTCGAGC-3’ (SEQ ID NO: 15). vi. Assays for EBV 9 (Epstein Barr), HHV-6B (Human Herpesvirus), and HHV-8 Assays for EBV (Epstein Barr), HHV-6B and HHV-8 were performed by methods previously reported (Keith et al., 2018). For EBV assays, Akata cells were induced to undergo a lytic infection with 50 µg/ml of a goat anti-human IgG antibody. Experimental compounds were diluted within plates; the cells were added and incubated for 72 h. For HHV-6 assays, compounds were serially diluted in plates then uninfected Molt-3 cells were added to each well. Infection was initiated by adding HHV-6B infected Molt-3 cells, at a ratio of approximately 1 infected cell for every 10 uninfected cells. Assay plates were incubated for seven days at 37°C. Assays for HHV-8 were performed in BCBL-1 cells. Similar plates were initiated without virus induction/addition and used for measuring cytotoxicity by the addition of CTG. For all assays, the replication of the virus was assessed by the quantification of viral DNA. For EBV, primers 5’-CCC AGG AGT CCC AGT AGT CA-3’ (SEQ ID NO: 16), and 5’-CAG TTC CTC GCCTTAGGTTG-3 (SEQ ID NO: 17), amplified a fragment corresponding to coordinates 96802–97234 in EBV genome (AJ507799). For HHV-8, 5’-TTC CCC AGA TAC ACG ACA GAA TC-3’ (SEQ ID NO: 18), reverse primer 5’-CGG AGC GCA GGC TAC CT-3’ (SEQ ID NO: 19), and probe 5'-(FAM) CCT ACG TGT TCG TCG AC (TAMRA)-3' (SEQ ID NO: 20). Plasmid pMP218 containing a DNA sequence corresponding to nucleotides 14120-14182 (AF148805.2) was used to provide absolute quantification of viral DNA. For HHV-6B, 5’-GTT AGG GTA TAC CGA TGT GCG TGA T-3’ (SEQ ID NO: 21), 5’-TAC AGA TAC GGA GGC AAT AGA TTC G-3’ (SEQ ID NO: 22), and 5'-(FAM) TCC GAA ACA ACT GTC TGA CTG GCA AAA-3' (SEQ ID NO: 23), were used to quantify virus DNA. Compound concentrations sufficient to reduce genome copy number by 50% were calculated from experimental data as well as compound cytotoxicity. Secondary assays are performed similarly, with the addition of 50 µg/ml of goat anti-human- IgG antibody to cells (EBV), initiation of infection by adding infected cells to uninfected cells (HHV-6B) or induction of HHV-8 in BCBL-1 cells - all performed and incubated for 1h prior to adding the cells to plates containing diluted compounds at 12 three-fold concentrations. vii. Assays for BK virus and JC virus. Primary assays for BKV and JCV were performed by methods previously reported (Keith et al., 2018). For BKV, compound dilutions were prepared in plates containing cells, subsequently infected and incubated for 7d. Total DNA was prepared and genome copy number was quantified by real time PCR using the primers 5’- AGT GGA TGG GCA GCC TAT GTA-3’ (SEQ ID NO: 24), 5’- TCA TAT CTG GGT CCC CTG GA-3’ (SEQ ID NO: 25), and probe 5’-6-FAM AGG TAG AAG AGG TTA GGG TGT TTG ATG GCA CAG TAMRA-3’ (SEQ ID NO: 26), (Leung et al., 2001). Plasmid pMP526 serves as the DNA standard for quantification purposes. Compounds that were positive in this assay were confirmed in a similar assay in 96-well plates according to established laboratory protocols with the compounds added 1h post infection to identify compounds that inhibit early stages of replication including adsorption and penetration. Genome copy number was determined by methods described above. Primary evaluation of compounds against JC virus were also performed by methods similar to those for BK virus primary assays but were done in COS7 cells and utilized the 1-4 strain of JCV in COS7 cells. Viral DNA was quantified using primers 5’-CTG GTC ATG TGG ATG CTG TCA-3’(SEQ ID NO: 27), and 5’-GCC AGC AGG CTG TTG ATA CTG-3’ (SEQ ID NO: 28), and probe 5’-6-FAM-CCC TTT GTT TGG CTG CT-TAMRA-3 (SEQ ID NO: 29), together with the plasmid pMP508 to provide a standard curve for absolute quantification. Secondary assays against JCV were also performed in COS7 cells by methods similar to those for BK virus to identify compounds that inhibited adsorption or penetration of the virus. viii. Assays for HPV (Human papillomavirus) Primary assay: An HPV11 replicon assay was developed and expresses the essential E1 and E2 proteins from the native promoter. The E2 origin binding protein interacts with the virus origin of replication and recruits the E1 replicative helicase which unwinds the DNA and helps to recruit the cellular DNA replication machinery (including DNA polymerases, type I and type II topoisomerases, DNA ligase, single-stranded DNA binding proteins, proliferating cell nuclear antigen). The replication complex then drives the amplification of the replicon which can be assessed by the expression of a destabilized NanoLuc reporter gene carried on the replicon. In this assay, the replicon (pMP619) is transfected into C-33 A cells grown as monolayers in 384- well plates. At 48 h post transfection, the enzymatic activity of the destabilized NanoLuc reporter is assessed with NanoGlo reagent. The reference compound for this assay is PMEG and its EC50 value is within the prescribed range of 2 - 9.2 µM and is similar to a compound reported previously (Beadle et al., 2016). Secondary Assay: HPV genome replication is done by methods similar to HPV 11 but in a plasmid, system utilizing HPV16 and/or HPV18. If only one strain is tested, an additional replicate is tested to ensure that the estimates of EC ₅₀ and EC ₉₀ values are more precise. Recent publications demonstrate our ability to perform these studies (Beadle et al., 2016). [0097] The results of the effectiveness of specific structures relating to different viruses are shown in Tables 1 to 7 set forth below. When reviewing the results, it should be noted that the lower the EC ₅₀ , the less the concentration of a drug is required to produce 50% of maximum effect and the higher the potency. [0098] Table 1 relates to the use of the following structures to treat Epstein-Barr Virus. Reviewing the EC ₅₀ values, the control showed an EC ₅₀ value of 3.92. However, CHK-03 showed an EC ₅₀ value of 2.97. [0099] Table 2 relates to the use of the following structure to treat Epstein-Barr Virus. Reviewing the EC ₅₀ values, the control showed an EC ₅₀ value of 5.49. Notably the CHK-05 structure showed an EC ₅₀ value of 69.85. [00100] Table 3 relates to the use of the following structure to treat MERS Coronavirus. Reviewing the EC ₅₀ values, the control showed an EC ₅₀ value of 0.036. Notably the CHK-05 molecule showed an EC ₅₀ value of >45. Notably this molecule also showed an SI value >10. [00101] Table 4 relates to the use of the following structure to treat Enterovirus. Reviewing the EC ₅₀ values, the control showed an EC ₅₀ value of 0.12. Notably the CHK-05 molecule showed an EC ₅₀ value of 24 and >36. [00102] Table 5 relates to the use of the following structure to treat Chikungunya virus. Reviewing the EC ₅₀ values, the control showed an EC ₅₀ value of 3.2 and 7.9 respectively depending on the assay. Notably the CHK-05 molecule showed an EC ₅₀ value of >68 and >42 again, depending on the assay. [00103] Table 6 relates to the use of the following structures to treat Ebola virus. Reviewing the EC ₅₀ values, the control showed an EC ₅₀ value of 12. The CDW3-002 molecule showed an EC ₅₀ of 30. The CHK-05 showed an EC ₅₀ of 18. Notably the CHK-05 molecule showed an EC ₅₀ value of >68 and >42 again depending on the assay. [00104] Table 7 relates to the use of the following structure to treat Dengue Virus. Reviewing the EC ₅₀ values, the control showed an EC ₅₀ value of 0.36 and 0.43 depending on the assays used. Notably the CHK-05 molecule showed an EC ₅₀ value of 79. [00105] Although the invention has been variously disclosed herein with reference to illustrative embodiments and features, it will be appreciated that the embodiments and features described hereinabove are not intended to limit the invention, and that other variations, modifications and other embodiments will suggest themselves to those of ordinary skill in the art, based on the disclosure herein. The invention therefore is to be broadly construed, as encompassing all such variations, modifications and altern

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