Iodo and diiodotyrosine epoxysuccinyl derivatives as selective inhibitors of cathepsin B

Abstract

Eight new analogs of l- trans-epoxysuccinyl- l-leucylamido(3-methyl)butane (E-64-c) containing Phe, Tyr, Tyr(1) or Tyr(I 2) 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(I 2) < Tyr < Phe < Leu for papain and Phe < Tyr < Tyr(I) < Leu < Tyr(I 2) for cathepsin B inactivation. Replacement of the l with the d- trans-epoxysuccinyl unit caused a 10–100-fold decrease in inhibitor potencies.