(S) -ML188 is a SARS-CoV 3-chymotrypsin-like protease (3CLpro) inhibitor (IC50: 1.5 μM) . (S) -ML188 has antiviral activity with an EC50 value of 12.9 μM against SARS-CoV. (S) -ML188 inhibits the activity of 3CLpro via non-covalent binding and can be used in the study of SARS-CoV[1].