Enantioselective ketoester reductions in water: a comparison between microorganism- and ruthenium-catalyzed reactions

In the search for green chemistry methods for the enantioselective reduction of ketoesters Saccharomyces cerevisiae- and ruthenium-catalyzed reactions in water have been investigated. The highest enantiomeric excesses for the reduction of α- and β-ketoesters have been obtained by S. cerevisiae. Chiral ruthenium catalysts are active for the reduction of all ketoesters with low to moderate enantioselectivities depending on the nature of the substrate and ligand. Interestingly, for several substrates both enantiomers of the hydroxyesters have been obtained according either to the catalytic method or to the structure of the ligand.

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(R)-Methyl 2-hydroxy-2-phenylacetateC9H10O3Ee = 99%[α]D20=-134 (c 1.0, MeOH)Source of chirality: reduction by Saccharomyces cerevisaeAbsolute configuration: (R)

(R)-Ethyl 2-hydroxy-2-phenylacetateC10H12O3Ee = 99%[α]D20=-132 (c 0.9, CHCl3)Source of chirality: reduction by Saccharomyces cerevisaeAbsolute configuration: (R)

(S)-Ethyl 3-hydroxy-3-phenylpropionateC11H14O3Ee = 83%[α]D20=-35.2 (c 0.5, CHCl3)Source of chirality: reduction by Saccharomyces cerevisaeAbsolute configuration: (S)

(R,S)-Methyl 2-hydroxycyclopentanecarboxylateC7H12O3De >99%; ee = 99%[α]D20=15 (c 1.95, CHCl3)Source of chirality: reduction by Saccharomyces cerevisaeAbsolute configuration: (1R,2S)