Kinetic Resolution of β-Amino Esters by Acylation Using Immobilized Penicillin Amidohydrolase
作者:Bryan H. Landis、Patrick B. Mullins、Karen E. Mullins、Ping T. Wang
DOI:10.1021/op0255130
日期:2002.7.1
Penicillin amidohydrolase [EC 3.5.1.11] was used to resolve stereoisomers of a beta-amino acid ester (ethyl 3-amino-5-(trimethylsilyl)-4-pentynoate) by phenylacetylation. After screening commercially available sources of the immobilized enzyme, one was found to be significantly more efficient, and this was developed at 1-L scale reaction. The effects of phenylacetic acid concentration, beta-amino acid ester concentration, and pH on bioconversion rates and side reactions were examined. The enzymatic reaction was monitored off-line by naphthoylation of samples and chiral analytical chromatography. The best conditions for the bioconversion were pH 5.7, 28 degreesC, and 14 000 units of enzyme activity per liter. The phenylacetic acid concentration was set at 50 g/L (0.37 M), and the amine at 100 g/L (0.47 M). Under these conditions, yields of the desired (S)amino acid ester were on the order of 90% with ee's of 95% or greater in less than 12 h. This process, along with a slight modification, was tested through 15 cycles at 0.4-L scale, and was scaled to 70 L. Recycle results extrapolated to approximately 25 reaction cycles before the enzyme lost 50% of its initial activity. Through three runs at 70 L, overall yield of (S)-amine was 42.7 +/- 0.6%, overall yield of (R)-phenylacetyl amide was 47.2 +/- 1.8%. The average ee of the amine (two runs) was 98.1 +/- 0.4%, for the amide the ee was 99.5 +/- 0.2%.