Enzymatic synthesis of a CCK-4 tripeptide fragment.

To synthesize a tripeptide derivative Phac-Met-Asp(OMe)-Phe -NH2, which is a fragment of the gastrin C-terminal tetrapeptide CCK-4, by enzymatic reaction. Three free enzymes, alpha-chymotrypsin, papain and thermolysin from acyl donor Phac-Met-OCam was involved in three steps. The choice of appropriate enzymes and solvents was selected. All enzymatic reactions were obtained in reasonable yields(63%-92%). FAB-MS and FD-MS verified the correct molecular mass of the peptides. Studies on the alpha-chymotrypsin catalyzed coupling reaction between Phac-Met-OCam and H-Asp(OMe)2 have focused on the low water content media. By papain catalyzed saponification of Phac-Met-Asp(OMe)2, alpha-methyl ester of aspartic acid is selectively hydrolyzed to retain beta-methyl ester, and Phac-Met-Asp(OMe)-OH and H-Phe-NH2 can be coupled efficiently by thermolysin.