Prodrugs of imidazotriazine and pyrrolotriazine C-nucleosides can increase anti-HCV activity and enhance nucleotide triphosphate concentrations in vitro.

A number of prodrugs of HCV-active purine nucleoside analogues 2'-C-methyl 4-aza-9-deaza adenosine 1, 2'-C-methyl 4-aza-7,9-dideaza adenosine 2, 2'-C-methyl 4-aza-9-deaza guanosine 3 and 2'-C-methyl 4-aza-7,9-dideaza guanosine 4 were prepared and evaluated to improve potency, selectivity and liver targeting. Phosphoramidate guanosine prodrugs (3a-3k and 4a, b) showed insufficient cell activity for further profiling. Striking enhancement in replicon activity relative to the parent was observed for phosphoramidate imidazo[2,1-f][1,2,4]triazine-4-amine adenosine prodrugs (1a-1p), but this was accompanied by an increase in cytotoxicity. Improved or similar potency without a concomitant increase in toxicity relative to the parent was demonstrated for phosphoramidate pyrrolo[2,1-f][1,2,4]triazine-4-amine adenosine prodrugs (2a-2k). Carbamate, ester and mixed prodrugs of 2 showed mixed results. Selected prodrugs of 2 were analysed for activation to the triphosphate, with most demonstrating much better activation in hepatocytes over replicon cells. The best activation was observed for a mixed phosphoramidate-3'ester (11) followed by a simple 3'-ester (10).