Discovery of Novel Small Molecule Anti-HCV Agents via the CypA Inhibitory Mechanism Using O-Acylation-Directed Lead Optimization

In this work, the relationship between cyclophilin A (CypA) and HCV prompted us to screen a series of small molecule CypA inhibitors which were previously reported by our group. Among them, compound 1, discovered as a non-immunosuppressive anti-HCV agent with an EC(50) value of 0.67 μM in a virus assay, was selected for further study. Subsequent chemical modification by O-acylation led to a novel class of molecules, among which compound 25 demonstrated the most potent anti-HCV activity in the virus assay (EC(50) = 0.19 μM), but low cytotoxicity and hERG cardiac toxicity. The following studies (a solution stability assay and a simple pharmacokinetic test together with a CypA enzyme inhibition assay) preliminarily indicated that 25 was a prodrug of 1. To the best of our knowledge, 25 is probably the most potent currently reported small molecule anti-HCV agent acting via the CypA inhibitory mechanism. Consequently, our study has provided a new potential small molecule for curing HCV infection.