Enzymatic preparation of optically pure t-butyl 6-chloro-(3R,5S)-dihydroxyhexanoate by a novel alcohol dehydrogenase discovered from Klebsiella oxytoca

摘要

Alcohol dehydrogenases can catalyze the inter-conversion of aldehydes and alcohols. The t-butyl 6-chloro(3R,5S)-dihydroxyhexanoate is a key chiral intermediate in the synthesis of statin-type drugs such as Crestor (rosuvastatin calcium) and Lipitor (atorvastatin). Herein, a novel alcohol dehydrogenase (named as KleADH) discovered from Klebsiella oxytoca by a genome mining method was cloned and characterized. The KIeADH was functionally overexpressed in Escherichia colt Rosetta (DE3) and the whole cell biocatalyst was able to convert t butyl 6-chloro-(5S)-hydroxy-3-oxohexanoate to t-butyl 6-chloro-(3R,5S)-dihydroxyhexanoate with more than 99% diastereomeric excess (de) and 99% conversion in 24 h without adding any expensive cofactors. Several factors influencing the whole cell catalyst activity such as temperature, pH, the effects of metal ions and organic solvent were determined. The optimum enzyme activity was achieved at 30 degrees C and pH 7.0 and it was shown that 1 mM Fe3+ can increase the enzyme activity by 1.2 times. N-hexane/water and n-heptane/water biphasic systems can also increase the activity of KleADH. Substrate specificity studies showed that KleADH also exhibited notable activity towards several aryl ketones with high stereoselectivity. Our investigation on this novel alcohol dehydrogenase KleADH reveals a promising biocatalyst for producing chiral alcohols for preparation of valuable pharmaceuticals.