7.11 Reduction: Enantioselective Bioreduction of C–C Double Bonds

Biocatalytic asymmetric activated alkene reduction by whole-cell suspensions and enzymes has been the subject of considerable research due to the often high efficiency and regio-, stereo-, and enantioselectivity of the reaction. Reactions catalyzed by enzymes are most often flavin-containing NAD(P)H-dependent enzymes from the Old Yellow Enzyme Family. These enzymes reduce the C=C bond of activated aldehydes, ketones, nitroalkenes, and carboxylic acids to produce a variety of industrially useful compounds. Baker's yeast and other microorganisms have been used extensively as robust, versatile whole-cell biocatalysts for activated alkene reduction and contain constitutive enzymes for coenzyme recycling. However, secondary reductions often occur, such as ketone reduction, due to the presence of other oxidoreductases. The use of isolated enzymes reduces the likelihood of side product formation, but requires the addition of a coenzyme-recycling system. This chapter will summarize the current knowledge of biocatalytic alkene reduction catalyzed by a wide range of microorganisms and isolated enzymes.