Directed Evolution of Carbonyl Reductase fromRhodosporidium toruloidesand Its Application in Stereoselective Synthesis oftert-Butyl (3R,5S)-6-Chloro-3,5-dihydroxyhexanoate

tert -Butyl (3 R,5 S )-6-chloro-3,5-dihydroxyhexanoate ((3 R,5 S )-CDHH) is a key intermediate of atorvastatin and rosuvastatin synthesis. Carbonyl reductase Rt SCR9 from Rhodosporidium toruloides exhibited excellent activity toward tert -butyl ( S )-6-chloro-5-hydroxy-3-oxohexanoate (( S )-CHOH). For the activity of Rt SCR9 to be improved, random mutagenesis and site-saturation mutagenesis were performed. Three positive mutants were obtained (mut-Gln95Asp, mut-Ile144Lys, and mut-Phe156Gln). These mutants exhibited 1.94-, 3.03-, and 1.61-fold and 1.93-, 3.15-, and 1.97-fold improvement in the specific activity and k cat / K m, respectively. Asymmetric reduction of ( S )-CHOH by mut-Ile144Lys coupled with glucose dehydrogenase was conducted. The yield and enantiomeric excess of (3 R,5 S )-CDHH reached 98 and 99%, respectively, after 8 h bioconversion in a single batch reaction with 1 M ( S )-CHOH, and the space-time yield reached 542.83 mmol L –1 h –1 g –1 wet cell weight. This study presents a new carbonyl reductase for efficient synthesis of (3 R,5 S )-CDHH.