Asymmetric reduction of aryl ketones with a new isolate Rhodotorula sp. AS2.2241

A yeast strain, Rhodotorula sp. AS2.2241, capable of reducing acetophenone and α-bromoacetophenone with high stereoselectivity, was isolated from soil samples through a novel screening procedure in which acetophenone was supplied in vapor state as the sole carbon and energy source. The biosynthesis of the ketone reductase in the yeast cells reached a maximum of 41.0 U/l at 20 h of cultivation. The reductase isolated from the Rhodotorula sp. cells was partially purified by 52.6-fold through a single column chromatography of DEAE–cellulose. The catalytic performance of the partially purified reductase was examined, and the highest activity was observed at pH 6.5 and 50 °C. The short-chain alkyl aldehydes such as acetaldehyde and those aldehydes or ketones with a benzoyl group were found to be good substrates for the reductase. In the preparative bioreductions of 50 mM acetophenone and 2 mM α-bromoacetophenone using resting cells of Rhodotorula sp. AS2.2241, (S)-(−)-1-phenylethanol (>99.5% enantiomeric excess (e.e.), 34.7% yield) and (R)-(−)-2-bromo-1-phenylethanol (>99.9% e.e., 19.9% yield) were obtained, respectively.