Microbial Biotransformations In Biphasic Systems: Formation Of (R)-2-Alkanols By Methylketone Reduction

The microbial enantioselective reduction of C4-C8 methylketones to the corresponding (R)-alcohols was investigated. Firstly the reduction of 2-octanone with Micrococcus luteus ATCC 9341 and Pichia etchellsii CBS 2011 was studied: these transformations afford (R)-2-octanol with incomplete enantioselectivity (enantiomeric excesses, e.e., of 80% and 50%, respectively). It was observed that stereoselectivity can be enhanced by performing the transformation in the presence of a suitable organic solvent. The presence of hydrophobic solvents avoids racemization of the alcohol formed, by continuously extracting it from the aqueous phase. The use of M. luteus and P. etchellsii in biphasic systems with n-heptane enabled the formation of (R)-2-octanol in high optical purity (> 97%). The same system was also used to carry out reductions of other methylketones with the two microorganisms. (R)-2-Alcohol formation was always observed with a high optical purity.