초록
Two robust stereocomplementary carbonyl reductases (<I>Dh</I>CR and<I>Cg</I>CR) were identified through rescreening the carbonyl reductase toolbox. Five reductases were returned through the activity and enantioselectivity assay for α-chloro-1-acetophenone and ethyl 4-chloro-3-oxo-butanate (COBE). Three reductases were stable at elevated substrate loading. Enzymatic characterization revealed that<I>Dh</I>CR and<I>Cg</I>CR were more thermostable. As much as 330 g COBE in 1 L biphasic reaction mixture was reduced to (<I>S</I>)- and (<I>R</I>)-3-hydroxy-4-chlorobutyrate by<I>Dh</I>CR and<I>Cg</I>CR (coexpressed with glucose dehydrogenase), with 92.5% and 93.0% yields, &gt;99% ee, and total turnover numbers of 53 800 and 108 000, respectively. Six other α-halohydrins were asymmetrically reduced to optically pure forms at a substrate loading of 100 g L<SUP>−1</SUP>. Our results indicate the potential of these two stereocomplementary reductases in the synthesis of valuable α-halohydrins for pharmaceuticals..