Asymmetric Reduction of Keto Acids by Use of Bakers' Yeast

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(1)Asymmetric Reduction by Use of Bakers' Yeast Homogenate Containing OxidoreductaseAliphatic delta-keto acids as substrate were reduced with the homogenate by use of NADPH as coenzyme. The products had the same configuration(R)as that for the products from the intact cells. The % ee was also>98% ee for both products. Since the material balance was better for the homogenate, it was suggested that the substrate was party lost in intact cells. However, no conclusion was derived about the possibility that the permeation of the substrate or the product through the cell wall or membrane is critical.(2)Effects of Metal SaltsAddition of MnCl_2 at a concentration of 1.5 mol/L enhanced the yield of bakers'yeast reduction from 64% to 84 89%. This result was found only for the substrate, n-C_5H_<11>COCH_2CH_2CO_2H, which is interesting but not explicable.(3)Asymmetric Reduction of Polyfunctional beta, delta-Diketo Acid by Use of Bakers' YeastThe main reduction product was beta-keto delta-hydroxy acid, which was found not to be reduced further to beta, delta-dihydroxy acid. beta-Hydroxy delta-keto acide was obtained as a minor product, which was found to be rather readily reduced to beta, delta-dihydroxy acid. The configuration was R for all chiral carbon atoms and the % ee was>99% ee. The delta-hydroxy compounds can be cyclized to beta-keto or beta-hydroxy delta-lactones.(4)Asymmetric Reduction of beta-Chloro gamma-Keto Acid by Use of Bakers' YeastRCOCHClCH_2CO_2H was reduced to the corresponding secondary alcohol : R=CH_3, config=S, 50 60% yield, >99% ee ; R=C_2H_5, S, 10%, 68% ee ; R=n-C_3H_7, R, 20%, 61% ee ; R=n-C_4H_9 n-C_6H_<13>, R, 20%, >98% ee.