Biocatalytic deracemization of racemic naphthyl alcohols by using a novel yeast isolate Rhodotorula kratochvilovae (MTCC 13029)

Enantiopure alcohols are key intermediates for the synthesis of a plethora of pharmaceuticals, agrochemicals and fine chemicals. Present study reports the deracemization of racemic naphthyl ethanols into their enantiopure S-forms by CHF-15P (Rhodotorula kratochvilovae, MTCC 13029) whole cells, isolated from the high altitude of the Himalayan mountain range. Initially, the biocatalyst was able to deracemize rac-1-(6-methoxy-2-naphthyl)ethanol to S-1-(6-methoxy-2-naphthyl)ethanol with 86.3% yield and 82.6% eeS. The studies on the effect of physicochemical parameters showed 92.3% yield with eeS>99% of product in a medium containing 2 mM substrate concentration and 2% glucose at 30 °C temperature, pH 7.0 (0.2 M sodium phosphate buffer), with 100 mg/mL cell concentration. In addition, the deracemization of rac-1-(6-methyl-2-naphthyl)ethanol and rac-1-(2-naphthyl)ethanol was achieved within 12 h at 30 °C with 96.4 and 98.8% of yield (98.2% and >99% eeS), respectively. The process of deracemization occurs via the formation of a ketone intermediate. The appearance of ketone has been demonstrated by high performance liquid chromatography (HPLC) and confocal laser scanning microscopy. However, rac-1-(1-naphthyl)ethanol and rac-1-(4-fluoro-1-naphthyl)ethanol were not deracemized under the same condition. In gram scale preparation, 92.8% yield with eeS>99% was obtained. Schematic representation for enantioselective cascade for the deracemization of (rac)-1a-c into S-enantiomers (S)-1a-c via ketonic intermediates by the process called stereoinversion using R. kratochvilovae cells. [Display omitted] •R. kratochvilovae is a novel isolate from the high altitude of the Himalayan Mountain.•The whole-cell of R. kratochvilovae deracemizes rac-naphthyl ethanols.•The strain is able to synthesize S-enantiomer from the racemic naphthyl alcohols.•The deracemization of rac-naphthyl ethanols occurs through the stereoinversion process.•Excellent enantiomeric excess (eeS ˃99%) and high yield (up to 98.8%) was achieved.