The synthesis, in vitro anti-HIV-1 activity, and decomposition pathways of several mononucleoside phosphotriester derivatives of 3'-azido-2',3'-dideoxythymidine (AZT) incorporating a new kind of carboxylate esterase-labile transient phosphate-protecting group, namely, S-acyl-2-thioethyl, are reported. All the described compounds showed marked antiviral activity in thymidine kinase-deficient CEM cells in which AZT was virtually inactive. The results strongly support the hypothesis that such pronucleotides exert their biological effects via intracellular delivery of the 5'-mononucleotide of AZT. This point was corroborated by decomposition studies in cell extracts and culture medium.
The decomposition pathways and kinetics in various biological media and the in vitro anti-HIV-1 and anti-HIV-2 activities of four derivatives of the 5'-mononucleotide of isoddA incorporating carboxylate esterase-labile transient phosphate protecting groups are reported and compared: namely, two mononucleoside aryl phosphoramidate derivatives 1a,b and two mononucleoside phosphotriester derivatives incorporating two S-acyl-2-thioethyl groups 2a,b. All four compounds show better antiviral activity, compared to the parent nucleoside analog isoddA. The results highlight that both types of compounds act as pronucleotides, i.e. they exert their antiviral effect via intracellular delivery of the 5'-mononucleotide of isoddA. The results may give insights for the design of new more efficient pronucleotides.
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