Add time:07/25/2019         Source:sciencedirect.com

Eight new analogs of l-trans-epoxysuccinyl-l-leucylamido(3-methyl)butane (E-64-c) containing Phe, Tyr, Tyr(1) or Tyr(I2) in place of Leu, were synthesized and tested as inhibitors of papain, bovine spleen cathepsin B, calpain I and II from porcine red cells and porcine kidney, respectively. By use of kinetic methods, the new E-64 analogs proved to irreversibly inactivate both papain and cathepsin B via reversible enzyme-inhibitor intermediates EI. Second-order rate constants for inactivation were in the range 3500-55 100 M−1s−1 for papain and 650–105 000 M−1s−1 for cathepsin B. For the inactivation of calpain I and II they ranged between 250 and 2000 M−1s−1 and were similar to those of the known E-64-c. The effectiveness of the amino acid contained in the inhibitors tested increased in the order Tyr(I) ≈ Tyr(I2) < Tyr < Phe < Leu for papain and Phe < Tyr < Tyr(I) < Leu < Tyr(I2) for cathepsin B inactivation. Replacement of the l with the d-trans-epoxysuccinyl unit caused a 10–100-fold decrease in inhibitor potencies.

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