Chalcones isolated from Angelica keiskei inhibit cysteine proteases of SARS-CoV

Two viral proteases of severe acute respiratory syndrome coronavirus (SARS-CoV), a chymotrypsin-like protease (3CL(pro)) and a papain-like protease (PLpro) are attractive targets for the development of anti-SARS drugs. In this study, nine alkylated chalcones (1-9) and four coumarins (10-13) were isolated from Angelica keiskei, and the inhibitory activities of these constituents against SARS-CoV proteases (3CL(pro) and PLpro) were determined (cell-free/based). Of the isolated alkylated chalcones, chalcone 6, containing the perhydroxyl group, exhibited the most potent 3CL(pro) and PLpro inhibitory activity with IC50 values of 11.4 and 1.2 mu M. Our detailed protein-inhibitor mechanistic analysis of these species indicated that the chalcones exhibited competitive inhibition characteristics to the SARS-CoV 3CL(pro), whereas noncompetitive inhibition was observed with the SARS-CoV PLpro.