aziridinyl peptides as inhibitors of cysteine proteases: Effect of a free carboxylic acid function on inhibition Original Research Article

Peptides containing aziridine-2,3-dicarboxylate (Azi) as electrophilic building block are evaluated as inhibitors of the cysteine proteases papain, cathepsin B, cathepsin L and clostripain. The influence of a free carboxylic acid as functional group at different positions of the inhibitor molecule on inhibition is analyzed. Structure–activity relationships and binding mode hypotheses are discussed. In contrast to the bacterial enzyme clostripain, the papain like mammalian proteases (cathepsins) are irreversibly inactivated by aziridinyl peptides. N-Unsubstituted aziridines are much more potent inhibitors of papain and cathepsins if they contain the free carboxylic acid attached to the aziridine ring (HOAzi-Leu-ProOBzl). Two free carboxylic acid functions at the aziridine ring are necessary for good inhibition of these enzymes by N-acylated aziridinyl peptides (BOC-Phe-Azi(OH)2). Chimeric bispeptidyl derivatives are selective CB inhibitors if the free acid is located at the C-terminus of the peptide (BOC-Phe-(EtO)Azi-Leu-ProOH). Clostripain is only inhibited by aziridinyl peptide esters.