Asymmetric reduction of alkyl-3-oxobutanoates mediated by Candida parapsilosis ATCC 7330 resulted in optically pure alkyl-3-hydroxybutanoates in good yields (up to 72%) and excellent enantiomeric excess (up to >99 %). A detailed and systematic optimisation study was necessary and was carried out to avoid the undesired transesterification reaction during the course of asymmetric reduction. Under optimised conditions, the (S)-alkyl hydroxyesters were produced predominantly except for the methyl ester which formed the (R)-enantiomer. To the best of our knowledge, the biocatalytic asymmetric reduction of isoamyl-3-oxobutanoate to (S)-isoamyl-3-hydroxybutanoate is reported here for the first time.

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Optically pure aliphatic β-hydroxy esters were prepared from their racemates by deracemisation using the biocatalyst Candida parapsilosis ATCC 7330. High optical purity (up to >99 %) and good yields (up to 71 %) of the product secondary alcohols were obtained. This study highlights the importance of optimization of reaction conditions using ethyl-3-hydroxybutanoate as the model substrate to improve the enantioselectivity (enantiomeric excess from 9 to 98 %). The present study emphasises the broad substrate scope of the biocatalyst towards deracemisation. This is the first report of Candida parapsilosis ATCC 7330-mediated deracemisation of various alkyl-3-hydroxybutanoates to produce either the (R)-enantiomers (methyl, ethyl, propyl, butyl, t-butyl, allyl-3-hydroxybutanoates) or (S)-enantiomers (pentyl, iso-amyl and iso-propyl-3-hydroxybutanoates).

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The title biocatalyst mediates the asymmetric, chemoselective reduction of nitroketones wherein the keto group is preferred with respect to the nitro group.