Evaluation of Coumarin and Neoflavone Derivatives as HCV NS5B Polymerase Inhibitors

Coumarins and coumestans represent an important family of compounds with diverse pharmacological properties. We recently identified coumestans as novel inhibitors of hepatitis C virus NS5B polymerase and predicted their binding in thumb pocket-1 (TP-1) of NS5B. As the coumarins are structurally related to coumestans by virtue of their common A- and B-rings, we postulated them to also exhibit similar binding interaction with NS5B and inhibit its polymerase function. We therefore investigated 24 coumarin and neoflavone derivatives as candidate NS5B inhibitors and identified 14 compounds inhibiting NS5B polymerase activity with IC50 values between 17 and 63m. Of these, the newly synthesized 6,8-diallyl-5,7-dihydroxycoumarin (8a) was produced in three steps in high chemical yield from floroglucinol and found to be the most potent of this series, exhibiting activity similar to the reference coumestan LQB-34. The binding site of 8a was mapped to TP-1 of NS5B by counter screening against P495L NS5B mutant, employed as a screen for TP-1 site binders. NS5B-TP-1-8a interaction map provided insight into 8a binding and offered clues for future SAR optimization.