Extended purine tricyclic and bicyclic nucleosides and nucleotides for use as antiviral therapeutics

A nucleoside compound selected from at least one of formula (I) or formula (II):

• wherein
• X1 and X2 are each independently selected from C, O, N, or S;
• X3 is C or N;
• X4 is O, NH, S, or CH2;
• X5 is O, NH, S, or CH2;
• Y1 and Y2 are each independently selected from H, OH, SH, ═O, F, NH2, NH-alkyl, O-alkyl, NH—OH, alkyl, CF3, Cl, CN, or N3;
• Z1 and Z2 are each independently selected from C or a heteroatom;
• R1 is H or cyano;
• R2 and R3 are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g., amino acid prodrugs);
• R4 is H, OH, N3, or various prodrugs (e.g., amino acid prodrugs);
• R5 is H, F, ethynyl or cyano;
• and
• R6 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;
• and/or formula (III)
• wherein
• X1 and X2 are each independently selected from C, O, N, or S;
• X3 is C or N;
• X4 is O, NH, S, or CH2;
• X5 is O, NH, S, or CH2;
• Y1 is OH, NH2, NH-alkyl, O-alkyl or NH—Ar
• Y2 is NH2, NH-alkyl, O-alkyl or NH—Ar
• R1 is H or cyano;
• R2 and R3 are each independently selected from H, OH, F, Cl, alkyl, ethynyl, or various prodrugs (e.g., amino acid prodrugs);
• R4 is H, OH, N3, or various prodrugs (e.g., amino acid prodrugs);
• R5 is H, F, ethynyl or cyano;
• and
• R6 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,
• or a pharmaceutically acceptable salt, isomer, hydrate, prodrug or solvate thereof.