Papain-catalyzed fragment synthesis of protected cholecystokinin derivatives

Abstract

Sodium salts of methyl esters of N-tert-butyloxycarbonyl-β-tert-butylaspartyl-O4-sulfotyrosine (II) or N-tert-butyloxycarbonyl-O4-sulfotyrosine (III) were condensed with amino components derived from peptide amides IVb-IVe and IVg (simulating the carboxy-terminal part of cholecystokinin) under catalysis with papain. Rates and yields of conversion of these peptides to the corresponding derivatives Ib-If were compared with the results reported previously for analogous papain-catalyzed fragment synthesis of the protected carboxy-terminal octapeptide of cholecystokinin Ia. In the condensation reactions with the individual amino components quantitative changes were observed in the ability of papain to catalyze the peptide bond synthesis which appeared as differences in the maximum yield (and the time required for achieving it) of the condensation reaction, monitored by HPLC. The observed differences are related not only with the distance of the amino acid substitution from the P'1 subsite in the given amino component but also with the side-chain structure of the substituting amino acid.