Cryptococcus laurentii as a new biocatalyst for the asymmetric reduction of substituted acetophenones

Immobilized cells of the yeast Cryptococcus laurentii attached to calcium alginate have been introduced as a biocatalyst in the asymmetric reduction of substituted acetophenones. Forty isolates of microorganisms belonging to this taxonomical yeast group were isolated from various samples. Immobilized cells of these isolates were screened as reducing agents for acetophenone 1a to its corresponding alcohol 1b. The four best isolates were selected and identified as Rhodotorula glutinis, Saccharomyces cerevisiae, Hansenula capsulata and C. laurentii by the VITEK 2 compact system. The use of the first three microorganisms is well known and therefore it was decided to explore C. laurentii as a new biocatalyst in organic reactions. The aim was to determine whether C. laurentii could be used to catalyse the bio-reduction of ketones to obtain the (R)- or (S)-isomer of the alcohol with high enantiomeric purity. The isolate C. laurentii EBK-19 was selected for further experiments and studied in detail. More than 70% of the ketones tested were obtained with almost complete conversion (100%), while all the ketones tested were converted to the corresponding (S)-isomer-alcohols in up to >99% enantiomeric excess (ee) under very mild reaction conditions. Amongst the chiral alcohols obtained, the enantiopure 1b obtained from the complete conversion of 1a using C. laurentii EBK-19 was produced on a large scale (9.3 g) using an immobilized cell reaction system. In conclusion, we have presented C. laurentii as a promising biocatalyst for the production of optically active phenylethanols.