Gamma-Ketobenzyl-Modified Nucleoside Triphosphate Prodrugs As Potential Antivirals

The antiviral activity of nucleoside reverse transcriptase inhibitors is often hampered by insufficient phosphorylation. Nucleoside triphosphate analogues are presented, in which the gamma-phosphate was covalently modified by a non-bioreversible, lipophilic 4-alkylketobenzyl moiety. Interestingly, primer extension assays using human immunodeficiency virus reverse transcriptase (HIV-RT) and three DNA-polymerases showed a high selectivity of these gamma-modified nucleoside triphosphates to act as substrates for HIV-RT, while they proved to be nonsubstrates for DNA-polymerases alpha, beta and gamma. In contrast to d4TTP, the gamma-modified d4TTPs showed a high resistance toward dephosphorylation in cell extracts. A series of acyloxybenzyl-prodrugs of these gamma-ketobenzyl nucleoside triphosphates was prepared. The aim was the intracellular delivery of a stable gamma-modified nucleoside triphosphate to increase the selectivity of such compounds to act in infected versus noninfected cells. Delivery of gamma-ketobenzyl-d4TTPs was proven in T-Iymphocyte cell extracts. The prodrugs were potent inhibitors of HIV-1/2 in cultures of infected CEM/O cells and more importantly in thymidine kinase-deficient CD4(+) T-cells.