Enzyme-catalyzed peptide segment condensation using 5(4H)-oxazolones as acyl donors

5(4H)-oxazolones are used as acyl donors in the condensation of enzyme-catalyzed peptide segment. Racemization and low yields are involved in the preparation of the peptides having 10 to 15 amino acids. The commercial peptide synthesizers used in the preparations reveal that a kinetically controlled approach, with acyl esters acting as donors and acylamides as nucleophiles, is favored in these enzymatic preparations, though earlier studies indicate that the 5(4H)-oxazolones are unstable for use in peptide synthesis. The oxazolones can be used in the protease-catalyzed condensations of the segment.