Stereoinversion of 1-arylethanols by Cyanidioschyzon merolae NEIS-1332

Enhancing cofactor regeneration of cyanobacteria for the light-powered synthesis of chiral alcohols

Cyanobacteria Synechocystis sp. PCC 6803 was exploited as green cell factory for light-powered asymmetric synthesis of aromatic chiral alcohols. The effect of temperature, light, substrate and cell concentration on substrate conversions were investigated. Under the optimal condition, a series of chiral alcohols were synthesized with conversions up to 95% and enantiomer excess (ee) > 99%. We found that the addition of Na₂S₂O₃ and Angeli's Salt increased the NADPH content by 20% and 25%, respectively. As a result, the time to reach 95% substrate conversion was shortened by 12 h, which demonstrated that the NADPH regeneration and hence the reaction rates can be regulated in cyanobacteria. This blue-green algae based biocatalysis showed its potential for chiral compounds production in future.

Demonstration of redox potential of Metschnikowia koreensis for stereoinversion of secondary alcohols/1,2-diols

The present work reports the Metschnikowia koreensis-catalyzed one-pot deracemization of secondary alcohols/1,2-diols and their derivatives with in vivo cofactor regeneration. Reaction is stereoselective and proceeds with sequential oxidation of (R)-secondary alcohols to the corresponding ketones and the reduction of the ketones to (S)-secondary alcohols. Method is applicable to a repertoire of racemic aryl secondary alcohols and 1,2-diols establishing a wide range of substrate specificity of M. koreensis. This ecofriendly method afforded the product in high yield (88%) and excellent optical purity (>98% ee), minimizing the requirement of multistep reaction and expensive cofactor.

Towards the discovery of alcohol dehydrogenases: NAD(P)H fluorescence-based screening and characterization of the newly isolated Rhodococcus erythropolis WZ010 in the preparation of chiral aryl secondary alcohols

A simple and reliable procedure was developed to screen biocatalysts with high alcohol dehydrogenase activity, efficient internal coenzyme regeneration, and high stereoselectivity. The strategy of activity screening in a microtitre plate format was based on the detection of fluorescence of NAD(P)H originating from the oxidation of alcohols. The primary and secondary screenings from soil samples yielded a versatile bacterial biocatalyst Rhodococcus erythropolis WZ010 demonstrating potential for the preparation of chiral aryl secondary alcohols. In terms of activity and stereoselectivity, the optimized reaction conditions in the stereoselective oxidation were 30 °C, pH 10.5, and 250 rpm, whereas bioreduction using glucose as co-substrate was the most favorable at 35 °C and pH 7.5 in the static reaction mixture. Under the optimized conditions, fresh cells of the strain stereoselectively oxidized the (S)-enantiomer of racemic 1-phenylethanol (120 mM) to acetophenone and afforded the unoxidized (R)-1-phenylethanol in 49.4 % yield and >99.9 % enantiomeric excess (e.e.). In the reduction of 10 mM acetophenone, the addition of 100 mM glucose significantly increased the conversion rate from 3.1 to 97.4 %. In the presence of 800 mM glucose, acetophenone and other aromatic ketones (80 mM) were enantioselectively reduced to corresponding (S)-alcohols with excellent e.e. values. Both stereoselective oxidation and asymmetric reduction required no external cofactor regeneration system.

Enantioselective dynamic process reduction of α- and β-tetralone and stereoinversion of resulting alcohols in a selected strain culture

α-Tetralone and β-tetralone were subjected to biotransformation by 14 fungal strains. Enantiomeric purity of the products depended on the reaction time. 3-Day transformation of α-tetralone in Absidia cylindrospora culture gave S-(+)-1,2,3,4-tetrahydro-1-naftol of 92 % ee, whereas longer biotransformation time resulted in decrease of ee value. 3-Day transformation of β-tetralone by the same strain gave predominantly S-(−)-1,2,3,4-tetrahydro-2-naftol, whereas after 9 days of the reaction, the R-enantiomer with 85 % ee was isolated. Transformation of β-tetralone by Chaetomium sp. KCh 6651 gave pure (S)-(−)-1,2,3,4-tetrahydro-2-naftol in high yield at the concentration of 1 g/l. In this process, a non-selective carbonyl reduction was observed, followed by a selective oxidation of the R-alcohol.