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 one or more protected amino groups;
• R1 is an optionally substituted N-linked amino acid or an optionally substituted N-linked amino acid ester derivative;
• R2 is selected from the group consisting of an optionally substituted aryl, an optionally substituted heteroaryl and an optionally substituted heterocyclyl;
• R3a and R3b are independently selected from the group consisting of hydrogen, an optionally substituted C1-6 alkyl, an optionally substituted C2-6 alkenyl, an optionally substituted C2-6 alkynyl, an optionally substituted C1-6 haloalkyl and aryl(C1-6 alkyl), provided that at least one of R3a and R3b is not hydrogen;
• or R3a and R3b are taken together to form a group selected from the group consisting of an optionally substituted C3-6 cycloalkyl, an optionally substituted C3-6 cycloalkenyl, an optionally substituted C3-6 aryl and an optionally substituted C3-6 heteroaryl;
• R4 is hydrogen;
• R5 is selected from the group consisting of hydrogen, —OR9 and —OC(═O)R10;
• R6 is selected from the group consisting of hydrogen, halogen, —OR11 and —OC(═O)R12;
• or R5 and R6 are both oxygen atoms and linked together by a carbonyl group;
• R7 is selected from the group consisting of hydrogen, halogen, an optionally substituted C1-6 alkyl, —OR13 and —OC(═O)R14;
• R8 is hydrogen or an optionally substituted C1-6 alkyl;
• R9, R11 and R13 are independently selected from the group consisting of hydrogen and an optionally substituted C1-6 alkyl;
• and
• R10, R12 and R14 are independently selected from the group consisting of an optionally substituted C1-6 alkyl and an optionally substituted C3-6 cycloalkyl;
• provided a compound of Formula (I) cannot have a structure selected from the group consisting of: