Aza-peptide epoxides, a new class of irreversible protease inhibitors, are specific for the clan CD cysteine proteases. The inhibitors have second-order rate constants up to 10(5) M(-1) s(-1), with the most potent epoxides having the S,S stereochemistry. The aza-Asn derivatives are effective legumain inhibitors, while the aza-Asp epoxides were specific for caspases. The inhibitors have little or no inhibition with other proteases such as chymotrypsin, papain, or cathepsin B.

Aza-peptide Michael acceptors are a new class of irreversible inhibitors that are highly potent and specific for clan CD cysteine proteases. The aza-Asp derivatives were specific for caspases, while aza-Asn derivatives were effective legumain inhibitors. Aza-Lys and aza-Orn derivatives were potent inhibitors of gingipain K and clostripain. Aza-peptide Michael acceptors showed no cross reactivity toward papain, cathepsin B, and calpain.