Access to Optically Active Aryl Halohydrins Using a Substrate-Tolerant Carbonyl Reductase Discovered from Kluyveromyces thermotolerans

By genome data mining, a carbonyl reductase tool box was designed and developed for chiral alcohol synthesis. On the basis of systematic comparison of the specific activity and substrate tolerance toward α-chloroacetophenone among reductases in this tool box, KtCR, a highly substrate-/product-tolerant carbonyl reductase from Kluyveromyces thermotolerans, was identified. The reduction of a series of substituted aryl ketones was investigated using this newly mined biocatalyst. Almost all of the ketones tested were asymmetrically reduced into corresponding chiral alcohols in 99% ee. Substrates with substituents adjacent to the carbonyl group or those with substituents on the para position of the phenyl ring were easier to reduce. For α-choloacetophenone as a representative substrate, as much as 154 g/L (1.0 M) of the substrate was asymmetrically reduced within merely 12 h by lyophilized cells of Escherichia coli/pET28-KtCR, resulting in an isolated yield of 92%, an enantiopurity of >99% ee, and a total turnover number of 5000, which was five times higher than the highest record reported so far. These results indicate the great potential of KtCR in practical synthesis of valuable aryl halohydrins as versatile chiral synthons.