PROTEASE-CATALYZED PEPTIDE-SYNTHESIS USING INVERSE SUBSTRATES - THE SYNTHESIS OF PRO-XAA-BONDS BY TRYPSIN

Benzyloxycarbonyl-L-proline p-guanidinophenyl ester is an "inverse substrate" for trypsin; i.e., the cationic center is included in the leaving group instead of being in the acyl moiety. This substrate can be used in trypsin-catalyzed acyl-transfer reactions leading to the synthesis of Pro-Xaa peptide bonds. The reaction proceeds about 20 times slower than reactions with similar alanine-containing substrates, but the ratio between synthesis and hydrolysis is more favorable. The investigation of a series of nucleophiles led to information about the specificity of the process. Nucleophiles differing only in the P'1-position show an increasing acyl transfer efficiency in the order Phe < Gly < Ley < Ser < Ala < Ile. C terminal elongation of the nucleophiles is of minor influence on their efficiency. The formation of an H bond between the acyl-enzyme and the nucleophile seems to play an important role in the aminolysis of the acyl-enzyme.