Improved stereoselective bioreduction of t-butyl 6-cyano-(5R)-hydroxy-3-oxohexanoate by Rhodotorula glutinis through heat treatment.

Optically pure t-butyl 6-cyano-(3R, 5R)-dihydroxyhexanoate ((R)-1b) is the key precursor for atorvastatin calcium, the most widely used cholesterol-lowering drug. In this work, a strain ZJB-09224 capable of asymmetrically reducing t-butyl 6-cyano-(5R)-hydroxy-3-oxohexanoate (1a) to corresponding optically pure (R)-1b was successfully isolated from soil sample, identified belonging to Rhodotorula glutinis based on the morphology, physiological tests, and the 18S rDNA sequence analysis. It was found that heat treatment of cell suspension at 45 °C for 25 Min significantly improved R. glutinis ZJB-09224 stereoselectivity. The asymmetric bioreduction of 1a was most efficient at pH 7.5, 35 °C, 50 mM (15.0 g L(-1) ) substrate concentration, 40.0 g DCW L(-1) cell loading size, 0.54 M (60.0 g L(-1) ) sodium lactate acting as co-substrate. Under these optimal conditions, 0.046 M (R)-1b was produced with de (diastereomeric excess) value of 99.2% after 40 H conversion. Moreover, R. glutinis ZJB-09224 has a broad substrate spectrum, making it a potential tool for some valuable chiral alcohol pharmaceutical intermediates synthesis.