Isatin compounds as noncovalent SARS coronavirus 3C-like protease inhibitors

A series of isatin derivatives were synthesized and tested against SARS CoV 3C-like protease. Substitutions at the N-1 and C-5 positions were examined to elucidate the differences in substrate binding sites of the rhinovirus 3C protease and SARS CoV 3C-like protease. Compound 5f shows significant inhibition with an IC50 of 0.37 mu M. Further study showed that, unlike the irreversible covalent binding of isatin derivatives to human rhinovirus 3C protease, the compounds tested in this study are all noncovalent reversible inhibitors.