Protease-catalyzed peptide synthesis: prevention of side reactions in kinetically controlled reactions.

One major problem in protease-catalyzed peptide synthesis is the occurrence of unwanted proteolytic side reactions. The objective of this study was to demonstrate that specific acyl donor esters can efficiently prevent the enzymatic hydrolysis of the peptide product. As a model system, we have studied the alpha-chymotrypsin-catalyzed synthesis of peptides which are specific chromogenic substrates for this enzyme. The leaving group of the carboxyl component was shown to be of major influence on this process. The accumulating protease-labile peptide product can be protected against enzyme action by a sufficient concentration of a specific acyl donor ester. The parameter alpha 1 that gives the ratio of second-order rate constants for the enzymatic hydrolysis of the peptide product and the acyl donor plays a key role in the synthesis of protease-labile peptides. We could establish that highly protease-labile peptides can be enzymatically synthesized in a homogeneous phase.