Protease-Catalyzed Oligomerization of Hydrophobic Amino Acid Ethyl Esters in Homogeneous Reaction Media Using L-Phenylalanine as a Model System

Enzymatic synthesis of oligopeptides from L-phenylalanine ethyl ester hydrochloride (L-Phe-Et center dot HCl) and other L-form hydrophobic amino acid ester hydrochlorides in water miscible organic cosolvents was studied. Different proteases, water miscible cosolvents, and effect of different ratios of water miscible cosolvents for protease-catalyzed oligo-phenylalanine [oligo(L-Phe)] were compared. The importance of the use of water miscible cosolvents in transforming reactions from heterogeneous to homogeneous conditions as a potent medium engineering tool for protease-catalyzed oligopeptide synthesis is highlighted. For example, at 0.125 M L-Phe-Et center dot HCl, 20% (v/v) methanol, 18.6 mg/mL bromelain, in phosphate buffer (0.25M, pH 8), 40 degrees C, for 3 h, oligo(L-Phe) precipitated from the solution to yield 45 +/- 5%, in contrast, in the absence of cosolvent oligo(L-Phe) yield of 29 +/- 5% was obtained. The following reaction conditions were optimized for bromelain catalyzed oligo(L-Phe) synthesis: pH, temperature, substrate, enzyme, and cosolvent concentrations. DPavg and chain length distribution in the product peptides were investigated by H-1 NMR and MALDI-TOF.