PREPARATION OF BOTH ENANTIOMERS OF AN ALPHA-HYDROXY KETONE VIA BIOCATALYTIC REDUCTION AND CHEMICAL OXIDATION

2-Hydroxy-2,6,6-trimethylcyclohexanone 1 is a key intermediate for the synthesis of naturally occurring bioactive metabolites, viz. 2A-B and 3. Both enantiomers of this key intermediate 1 were obtained by stere ospecific reduction using Bakers' yeast under nonfermenting conditions followed by chemical oxidation. Free as well as immobilized cells wer e tested in aqueous and organic media for their ability to catalyze th e stereospecific reduction of the parent ketone 1. Preparative scale b iotransformation of 1 in aqueous medium using free cells of Bakers' ye ast produced two diastereomeric alcohols 4 and 5 at a ratio of approxi mately 1:4 and 9.1% and 36.4% chemical yields, respectively. The reduc ed products exhibited high enantiomeric excess (>90%) as analyzed by H -1 and C-13-NMR spectroscopy. Unreduced hydroxy ketone was found to be highly enriched in S (-)-1, while chemical oxidation of the diol 5 ga ve R (+) 1. A reversal of diastereoselectivity was observed when an or ganic medium was used for biotransformation.