γ‑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 γ-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 γ-modified nucleoside triphosphates
to act as substrates for HIV-RT, while they proved to be nonsubstrates
for DNA-polymerases α, β, and γ. In contrast to
d4TTP, the γ-modified d4TTPs showed a high resistance toward
dephosphorylation in cell extracts. A series of acyloxybenzyl-prodrugs
of these γ-ketobenzyl nucleoside triphosphates was prepared.
The aim was the intracellular delivery of a stable γ-modified
nucleoside triphosphate to increase the selectivity of such compounds
to act in infected versus noninfected cells. Delivery of γ-ketobenzyl-d4TTPs
was proven in T-lymphocyte cell extracts. The prodrugs were potent
inhibitors of HIV-1/2 in cultures of infected CEM/0 cells and more
importantly in thymidine kinase-deficient CD4+ T-cells.