Regio- and Stereoselective Reduction of Substituted 1.3-Dicarbonyl Compounds by Use of Bakers' Yeast

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1. Effects of Additives of the Bakers' Yeast Reduction of 1-Chloro-2,4-alkanediones---The % ee values of reduction products were found to be enhanced by addition of SrCl_2 in 2 mol/L to the aqueous reaction solution. Other metal chlorides also exhibited similar effects, though not so large. The effects can be attributed to selective activation or inhibition of additives toward plural reducing enzymes.2. Bakers' Yeast Reduction of 1-Acetoxy-2,4-alkanediones ---The reduction produced (S)-1-acetoxy-2-hydroxy-4-alkanones in 40 - 90% ee, as compared with the reduction of 1-acetoxy-2-alkanones with 95 - >99% ee. The somewhat diminished % ee values can be attributed to the presence of an oxo functional group at C-4. The oxo group effectively suppressed the hydrolysis of the acetoxy group, which occurred for 1-acetoxy-2-alkanones and produces 1,2-diols as by-product. The optically active trifunctional products are useful as chiral synthons.3. Highly Efficient Asymmetric Reduction by Use of Bakers' Yeast Cell-Free Extract---The cell-free extract was found to reduce 1-acetoxy-2-alkanones to 1-acetoxy-2-alkanols in 59 - 88% yield and 95 - >99% ee by use of a catalytic amount of NADPH with glucose as hydride source and without addition of any enzyme for the cofactor regeneration. This method is expected to be applicable to 1-chloro- and 1-acetoxy-2,4-alkanediones.