Pyrido[2,3-d]pyrimidine and pyrimido[4,5-d]pyrimidine nucleosides

A nucleoside analog according to the formula (I)

• 15
• wherein
• A is O, S, CH2;
• R2, R2′, R3, and R3′ are independently selected from H, F, OH, NH2, CN, N3, CONH2, and R, where R is lower alkyl, lower alkenyl, lower alkynyl, or lower acyl, and optionally containing at least one of a heteroatom and a functional group;
• or R2 and R2′ together, or R3 and R3′ together are selected from ═CH2, ═CHR″, ═CR″2, ═NR″, where R″ is H, F, OH, CN, N3, CONH2, lower alkyl, lower alkenyl, lower alkynyl, or lower acyl;
• R4 and R5′ are independently selected from H, lower alkyl, lower alkenyl, lower alkynyl, or aralkyl, and optionally containing at least one of a heteroatom and a functional group;
• R5 is H, OH, OP(O)(OH)2, P(O)(OH)2, OP(O)(OR′″)2, or P(O)(OR′″)2, where R′″ is a masking group;
• and
• B is selected from the group of heterocyclic radicals consisting of formula (II), (III), (IV), and (V)
• 16
• wherein X is H, NH2 or OH;
• Y is H, NH2, or halogen;
• Z1 in formula (II) and (IV), and Z3 in formula (III) and (V) is O, S, NR″, CHM, or CM2;
• Z1 in formula (III) and (V), and Z3 in formula (II) and (IV) is N, CH, or CM;
• Z2 is N, CH, or CM;
• where M is F, Cl, Br, OH, SH, NH2, CN, COOR″, C(═NH)NH2, lower alkyl, lower alkenyl, lower alkynyl, aralkyl, or aryl.