Synthesis of tetrapeptide Bz-RGDS-NH2 by a combination of chemical and enzymatic methods

The tetrapeptide Bz-Arg-Gly-Asp-Ser-NH2 (Bz-RGDS-NH2) was successfully synthesized by a combination of chemical and enzymatic methods in this study. Firstly, the precursor tripeptide Gly-Asp-Ser-NH2 (GDS-NH2) was synthesized by a novel chemical method in four steps including chloroacetylation of l-aspartic acid, synthesis of chloroacetyl l-aspartic acid anhydride, the synthesis of ClCH2COAsp-SerOMe and ammonolysis of ClCH2COAsp-SerOMe. Secondly, lipase (PPL) was used to catalyze the formation of Bz-RGDS-NH2 in aqueous water-miscible organic cosolvent systems using Bz-Arg-OEt as the acyl donor and GDS-NH2 as the nucleophile. The optimum conditions were Bz-Arg-OEt 50 mM; GDS-NH2 400 mM; 10 °C, 0.1 M phosphate buffer, pH 7.5; 60% DMF or 58% DMSO, PPL: 10 mg ml−1 with the maximum yields of the tetrapeptide of 73.6% for DMF and 70.4% for DMSO, respectively. The secondary hydrolysis of the tetrapeptide product did not take place due to the absence of amidase activity of lipase.