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The stereoselective baker's yeast reduction of various N-protected piperidone-carboxylic acids have been studied, and the enantioselectivity was found to be widely dependent on whether fermenting or non-fermenting conditions were employed. Thus reaction of N-tert-butoxycarbonyl-4-oxopiperidine-3-carboxylic acid ethyl ester (6) with fermenting baker's yeast gave almost racemic N-tert-butoxycarbonyl-4-hydroxypiperidine-3-carboxylic acid ethyl ester (7), however, with complete diastereoselectivity. Reduction of 6 with non-fermenting yeast gave 7 with a 24-41% enantiomeric excess. Similarly, reduction of N-tert-butoxycarbonyl-3-oxopiperidine-4-carboxylic acid ethyl ester (17) with fermenting baker's yeast gave racemic N-tert-butoxycarbonyl-3-hydroxypiperidine-4-carboxylic acid ethyl ester [(+/-)-18] diastereoselectively. A convenient method for determining the enantiomeric excess of the hydroxypiperidine carboxylic acids derivatives was found in the reaction with Sanger's reagent followed by HPLC on a chiral column.

acta chemica scandinavica/acta chemica scandinavica. b, organic chemistry and biochemistry/acta chemica scandinavica. a, physical and inorganic chemistry/acta chemica scandinavica. series b. organic chemistry and biochemistry/acta chemica scandinavica. series a, physical and inorganic chemistry

A Study of Baker's Yeast Reduction of Piperidone-carboxylates.