THERMOSTABLE ENZYMES IN ORGANIC-SYNTHESIS .2. ASYMMETRIC REDUCTION OF KETONES WITH ALCOHOL-DEHYDROGENASE FROM THERMOANAEROBIUM-BROCKII

The asymmetric reduction of aliphatic acyclic ketones (C4-C10 substrates) is efficiently achieved by using alcohol dehydrogenase from Thermoanaerobium brockii either as a homogenous, heat-treated, cell-free extract or follwoing immobilization on a solid support. Both methods are superior to the use of whole-cell fermentation. The experimental conditions for working with TBADH were studied and optimized in order to improve reaction rates and the optical purity of the product. An interesting substrate size-induced reversal of stereoselectivity was observed. The smaller substrates (methyl ethyl, methyl isopropyl, or methyl cyclopropyl ketones) are reduced to R alcohols, whereas the higher ketones form the S enantiomer.