LIPASE-CATALYZED PEPTIDE-SYNTHESIS USING Z-AMINO ACID-ESTERS AS ACYL DONORS IN AQUEOUS WATER-MISCIBLE ORGANIC-SOLVENTS

The lipase(PPL)-catalyzed peptide synthesis(Z-Phe-Phe-NH2) in aqueous water-miscible organic cosolvents was studied using Z-Phe-OEt as an ester substrate and Phe-NH2 as a nucleophile. It was found that peptide yield increased with an increase of the concentration of DMF. At a higher concentration than 50%(v/v), however, peptide yield decreased rapidly. The optimal pH of an aqueous buffer and concentration of Phe-NH2 were 8 and 10-fold excess over Z-Phe-OEt, respectively. DMF, MeOH and DMSO were found to be effective cosolvents to promote peptide synthesis. The effect of reaction temperature was studied. It was found that both selectivity for peptide synthesis and the stability of PPL increased when the temperature was lowered. The selectivity reached about 90% at -10-degrees-C where the peptide synthesis became rather slow. The rate of peptide synthesis in aqueous-organic solvent mixture was good at room temperature. In a typical experiment (Z-Phe-OEt: 20 mM, Phe-NH2: 200 mM, 10-degrees-C, 50% DMF, PPL: 4 mgmL-1), Z-Phe-OEt was consumed almost completely within 6 h, yielding about 80% Z-Phe-Phe-NH2. The specificity of ester substrates toward PPL was also studied.