Membrane Permeable, Bioreversibly Modified Prodrugs of Nucleoside Diphosphate-γ-Phosphonates

Nucleoside
reverse transcriptase inhibitors (NRTIs) are widely
used as antiviral and anticancer agents, although they require intracellular
phosphorylation into their antivirally active form, the triphosphorylated
nucleoside analogue metabolites. We report on the synthesis and characterization
of a new class of nucleoside triphosphate analogues comprising a C-alkyl-phosphonate
moiety replacing the γ-phosphate. These compounds were converted
into bioreversibly modified lipophilic prodrugs at the γ-phosphonate
by the attachment of an acyloxybenzyl (ester) or an alkoxycarbonyloxybenzyl
(carbonate) group. Such compounds formed γ-C-(alkyl)-nucleoside
triphosphate analogues with high selectivity because of an enzyme-triggered
delivery mechanism. The latter compounds were very stable in CD4+ T-lymphocyte (CEM cell) extracts, and they were substrates
for HIV-reverse transcriptase without being substrates for DNA-polymerases
α, β, and γ. In antiviral assays, the excellent
antiviral activity of the prodrugs that was found in CEM/0 cells was
completely kept in CEM/TK– cells. The activity was
improved by 3 logs as compared to the parent nucleoside d4T.