Synthesis of cholecystokinin peptide CCK-4 exclusively by enzymatic methods

The synthesis of CCK-4 (H-Trp-Met-Asp-Phe-NH2) by using enzymes exclusively was described. As protection group for the amino group we used the Phenylacetyl group (Phac) which had been cleaved at the end of the synthesis with Penicillin G Amidase (PGA) without affecting the peptide bonds. Thus, beginning with Phac-Trp-OH we had successfully synthesized the target peptide with following 4 enzymes, alpha-Chymotrypsin, Papain, Thermolysin and PGA in four reaction steps. All reactions were carried out in aqueous buffer in reasonable yields (> 65%). FAB-MS or FD-MS verified the correct molecular mass of all peptides.