Asymmetric biocatalytic reduction of ketones using hydroxy-functionalised water-miscible ionic liquids as solvents

Bi- and monophasic ionic liquid (IL)/buffer systems were successfully employed for the biocatalytic reduction of ketones catalysed by the alcohol dehydrogenase ADH-‘A’ from Rhodococcus ruber via hydrogen transfer. Two different catalyst preparations were employed, namely recombinant ADH-‘A’ ‘immobilised’ in Escherichia coli and partially purified ADH-‘A’. For biphasic systems conversions were acceptable until 20% v v−1 of IL. In contrast, hydroxy-functionalised ‘Tris-like’-ILs were successfully employed in monophasic systems up to 90% v v−1 IL. The use of these solvents allowed highly stereoselective enzymatic carbonyl reductions at substrate concentrations from 1.2 to 1.5 M.

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