Prodrugs of γ-Alkyl-modified Nucleoside Triphosphates - improved Inhibition of HIV Reverse Transcriptase.

: The development of nucleoside triphosphate prodrugs is one option to apply nucleoside reverse transcriptase inhibitors. Here, we report on the synthesis and evaluation of of d4TTP analogues in which the γ-phosphate was modified covalently by lipophilic alkyl residues and on acyloxybenzyl-prodrugs of such γ-alkyl-modified d4TTPs . Thus, the intracellular delivery of γ-alkyl-d4TTP was aimed. . Selective formation of γ-alkyl-d4TTP was proven with esterase and in CD4+-cell extracts. In contrast to d4TTP, γ-alkyl-d4TTPs proved highly stable against dephosphorylation. Primer extension assays with HIV-RT and DNA-polymerases α, β or γ showed that γ-alkyl-d4TTPs were substrates for RT only. In antiviral assays, compounds were highly potent inhibitors of HIV-1 and HIV-2 also in thymidine kinase-deficient T-cell cultures (CEM/TK-). Thus, the intracellular delivery of such γ-alkyl-NTPs may potentially lead to a higher selectivity of NTPs towards the viral polymerase to act in virus-infected cells.