Pepsin‐catalyzed peptide synthesis

The use of pepsin as a catalyst for the synthesis of peptide bonds was investigated. It is shown that the enzyme enables the preparation of several protected dipeptides and tripeptides containing two adjacent aromatic residues of the type P‐Al‐Phe‐Y, P‐PHe‐Ar‐Y, or P‐AR‐Phe‐Y where P and Y are amino and carboxyl protecting groups, AL is an aliphatic amino acid residue, and Ar is an aromatic, amino acid residue. They yields are in the rang 25–97%. The high yields, combined with the enzyme's stereospecificity, permit the isolation of optically pure enantiomers from racemic mixtures. For example, when Z‐DL‐Ph‐OH is allowed to react with an excess of H‐L‐Phe‐NH2, the stereoisomer Z‐L‐Phe‐L‐Phe‐NH2 is obtained in practically quantitative yield. At the same time, the unreacted, optically pure Z‐D‐Phe‐OH can be recovered (Z = carbobenzyloxy, Phe = phenylalanine). The advantages and disadvantages of the enzymatic coupling procedure as a possible routine method for peptide synthesis are discussed.