Synthesis, antiviral activity and enzymatic phosphorylation of 9-phosphonopentenyl derivatives of guanine

(E)-9-(5-Phosphonopent-4-enyl)guanine and (E)-9-[3-(hydroxymethyl)-5- phosphonopent-4-enyl]guanine which bear a vinyl phosphonate moiety as a mimic of the phosphate group were synthesized. Their activities against human immunodeficiency virus type-1 (HIV-1), herpes simplex virus type-1 (HSV-1) and human cytomegalovirus (HCMV) were evaluated in vitro in parallel with those of 9-(5-phosphonopentyl)guanine and 9-(5,5-difluoro-5- phosphonopentyl)guanine. Both vinyl phosphonates exhibited anti-HIV-1 and anti-HCMV activities, whereas the methyl- and difluoromethyl phosphonate analogues were inactive. The selectivity index, calculated as the ratio of the toxicity for the host cells (50% reduction in cell viability or in [methyl-3H]thymidine incorporation) to the 50% inhibitory concentration for HIV-1 replication, was the highest for (E)-9-[3-(hydroxymethyl)-5-phosphonopent-4-enyl]guanine. The acyclonucleotide analogues were also studied as substrates of guanylate kinase, an enzyme believed to play a critical role in the conversion of acyclic phosphate and phosphonate derivatives of guanine to their antivirally active diphosphate derivatives. (E)-9-(5-Phosphonopent-4- enyl)guanine and (E)-9-[3-(hydroxymethyl)-5-phosphonopent-4-enyl]guanine were good substrates of guanylate kinase, being phosphorylated with efficiencies of 14 and 36% of that determined for GMP, respectively. These results contrast with the poor efficiency found for 9-(5-phosphonopentyl)guanine (0.3%) and the lack of phosphorylation of 9-(5,5-difluoro-5-phosphonopentyl)guanine by guanylate kinase (Navé et al. (1992) Arch. Biochem. Biophys. 295, 253-257). The role of the vinyl phosphonate group in the expression of the anti-HIV-1 activity of the phosphonopentenyl derivatives of guanine is discussed.