Substituted nucleotide analogs

A compound of Formula (I) or a pharmaceutically acceptable salt thereof:

• wherein:
• B1 is an optionally substituted heterocyclic base or an optionally substituted heterocyclic base with a protected amino group;
• R1 is selected from the group consisting of O−, OH, an optionally substituted N-linked amino acid and an optionally substituted N-linked amino acid ester derivative;
• R2 is absent or selected from the group consisting of hydrogen, an optionally substituted aryl, an optionally substituted heteroaryl, an optionally substituted heterocyclyl and
• wherein R6, R7 and R8 are independently absent or hydrogen, and n is 0 or 1;
• provided that when R1 is O− or OH, then R2 is absent, hydrogen or
• R3 is selected from the group consisting of hydrogen, halogen, —OR9 and —OC(═O)R10;
• R4 is selected from the group consisting of halogen, —OR11 and —OC(═O)R12;
• or R3 and R4 are both oxygen atoms and linked together by a carbonyl group;
• R5 is selected from the group consisting of an optionally substituted C2-6 alkenyl, an optionally substituted C2-6 alkynyl and an optionally substituted C3-6 cycloalkyl;
• or R4 and R5 together form —(C1-6 alkyl)-O— or —O—(C1-6 alkyl)—;
• R9 and R11 are independently hydrogen or an optionally substituted C1-6 alkyl;
• and
• R10 and R12 are independently an optionally substituted C1-6 alkyl or an optionally substituted C3-6 cycloalkyl.