Sub Micromolar Inhibitors of HCV Generated from Inactive Nucleosides by Application of ProTide Technology

We report the application of our phosphoramidate ProTide technology to various 4′-substituted ribonucleoside analogues, designed as potential inhibitors of hepatitis C virus (HCV) (Fig. 1). Thus, ProTides were prepared from 4′-azidouridine (AZU), -cytidine (AZC), -adenosine (AZA) and -5-methyluridine (AZMeU), besides other 4′-substituted uridines and cytidines. In each case, ProTide families included variations in the aryl, ester, and amino acid regions. A number of compounds showed potent inhibitory properties in cell culture without detectable cytotoxicity. These results confirm that phosphoramidate ProTides can deliver monophosphates of ribonucleoside analogues and suggest a potential path to the generation of novel antiviral agents against HCV infection. Of particular note was the sub-μM potency displayed by certain ProTides of AZU; a nucleoside analogue, which was itself inactive in the assay. In some cases, we were able to separate, and separately evaluate the phosphate stereoisomers generated in the synthesis; in a few cases the absolute phosphate stereochemistry was solved (Fig. 2). The generic message is that ProTide synthesis from inactive parent nucleosides may be a warranted drug discovery strategy.