NOVEL PEPTIDYL ALPHA-KETO AMIDE INHIBITORS OF CALPAINS AND OTHER CYSTEINE PROTEASES

A series of new dipeptidyl alpha-keto amides of the general structure R(1)-L-Leu-D,L-AA-CONH-R(2) were synthesized and evaluated as inhibito rs for the cysteine proteases calpain I, calpain II, and cathepsin B. They combine 10 different N-protecting groups (R(1)), 3 amino acids re sidues in P1 (AA), and 44 distinct substituents on the cx-keto amide n itrogen (R(2)) In general, calpain II was more sensitive to these inhi bitors than calpain I, with a large number of inhibitors displaying di ssociation constants (K-i) in the 10-100 nM range. Calpain I was also effectively inhibited, but very low K-i values were observed with a sm aller number of inhibitors than with calpain II. Cathepsin B was weakl y inhibited by most compounds in this study. The best inhibitors for c alpain II were Z-Leu-Abu-CONH-CH2-CHOH-C6H5 (K-i = 15 nM), Z-Leu-Abu-C ONH-CH2-2-pyridyl (K-i = 17 nM), and Z-Leu-Abu-CONH-CH2-C6H3(3,5(OMe)( 2)) (K-i = 22 nM). The best calpain I inhibitor in this study was Z-Le u-Nva-CONH-CH2-2-pyridyl (K-i = 19 nM). The peptide alpha-keto amide Z -Leu-Abu-CONH-(CH2)(2)-3-indolyl was the best inhibitor for cathepsin B (K-i = 31 nM). Some compounds acted as specific calpain inhibitors, with comparable activity on both calpains I and II and a lack of activ ity on cathepsin B (e.g., 40, 42, 48, 70). Others were specific inhibi tors for calpain I (e.g., 73) or calpain II (e.g., 18, 19, 33, 35, 56) . Such inhibitors may be useful in elucidating the physiological and p athological events involving these proteases and may become possible t herapeutic agents.