[reaction: see text] An enzyme-compatible biphasic reaction media for the asymmetric biocatalytic reduction of ketones with in situ cofactor regeneration has been developed. In this biphasic reaction media, which is advantageous for reactions at higher substrate concentrations, both enzymes (alcohol dehydrogenase and FDH from Candida boidinii) remain stable. The reductions with poorly water-soluble ketones were carried out at substrate concentrations of 10-200 mM, and the optically active (S)-alcohols were formed with moderate to good conversions and with up to >99% ee.
A practical and highly efficient biocatalytic synthesis of optically active (R)-4-fluorophenylethan-1-ol has been developed based on reduction of the corresponding 4-fluoroacetophenone in the presence of a tailor-made recombinant whole-cell biocatalyst, containing an alcohol dehydrogenase and a glucose dehydrogenase. The reaction proceeds in a pure aqueous solvent media at a substrate concentration of ca. 0.5 M, and gives the desired product with high conversion (> 95 %), good yield (87 %) and with an excellent enantioselectivity of > 99 % ee. In addition, activity tests further showed that also the analogous 2-and 3-fluoroacetophenones are promising substrates.
A practical biocatalytic method for the synthesis of aliphatic b-halogenated (S)-alcohols as epoxide precursors by means of an enantioselective reduction of the corresponding ketones with recombinant whole cells, bearing an alcohol dehydrogenase and a glucose dehydrogenase, was developed. The biotransformations operate at high substrate concentrations of up to 208 g/L, and afford the (S)-b-halohydrins with both high conversions of > 95 % and enantioselectivities of > 99 % ee. Baseinduced cyclization of the b-halohydrin intermediates gave the desired (S)-epoxides in high yield and enantiomeric purity (> 99 % ee).
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