Papain inhibitions by optically active E-64 analogs.

Modification of E-64 focused on the terminal agmatine for practical use led to some potent analogs which were successfully obtained by a stereoselective synthesis using D-tartaric acid as a starting material. Ep-475 (id. E-64-c), in which the agmatine was replaced by 3-methyl-butylamine, was found to react with the essential SH of papain in accord with the decrease of activity. [3H]Ep-475 was irreversibly incorporated into papain in an equimolar ratio. None of the analogs showed any effect on thiol enzymes other than proteolytic ones.