Lipase-catalyzed enantioselective hydrolysis of N-protected racemic non-protein amino acid esters

Abstract

Porcine pancreatic lipase (PPL)-catalyzed enantioselective hydrolysis of N-benzyloxycarbonyl-dl-amino acid esters (Z-dl-AA-ORs) was studied for the optical resolution of a variety of non-protein amino acids. The ester moiety (R) of the substrate affected the rate of hydrolysis significantly. The glyceryl (Gl) and carbamoylmethyl (Cam) esters were found to be highly reactive substrates. The hydrolysis of the Gl esters (Z-dl-AA-OGls) of both aliphatic and aromatic amino acids was examined in acetonitrile containing 70% (v/v) of 0.02 M phosphate buffer (pH 7.0) at 30°C. With all amino acids tested, the corresponding l-enantiomers were hydrolyzed preferentially. PPL favored aromatic amino acids, such as phenylalanine and p-chlorophenylalanine, leading to completion of the hydrolysis within 20 min with excellent enantioselectivities (E>100). The PPL-catalyzed hydrolysis of the corresponding Cam esters (Z-dl-AA-OCams) was also examined under the same reaction conditions. Although the hydrolysis of the Cam esters was rapid, the l-enantioselectivities were rather poor with aromatic amino acids, such as 2-phenylglycine and homophenylalanine.