Structure and synthesis of E-64, a new thiol protease inhibitor.

E-64, a new thiol protease inhibitor, was isolated from a mold, as described previously.1) This was proved to consist of each one mole of L-leucine, agmatine and L-trans-epoxysuccinic acid by the analysis of the digestion products of E-64 by pronase. Moreover, the absolute structure of E-64 was assumed to be N-[N-(L-3-trans-carboxyoxiran-2-carbonyl)-L-leucyl]-agmatine and the identity was established by the comparison with its optical isomer which was obtained synthetically. The difference of optical activity of trans-epoxysuccinic acid gave no effect on papain inhibitory activity.