Application of DMSO reductase to asymmetric synthesis and its large scale praparation of the enzyme.

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Dimethyl sulfoxide reductase (DMSO-R) isolated from the photosynthetic denitrifyingbacterium, Rhodobacter sphaeroides f.sp. denitrificans, reduces not only varieties of sulfoxides to the corresponding sulfides but also N-oxides to their reduced forms. In the case of sulfoxide reduction, the enzyme recognizes the stereochemistry of asymmetric sulfoxides, i.e., (S) -methylphenylsulfoxide (MPSO) of the racemic mixtureis exclusivelyreduced to the sulfide and 100% e.e.(R) isomer is recovered. MPSO and other alkylaryl sulfoxides (RArSO) were synthesized and assayd for the stereoselectivity of DMSO-R as well as for the kinetic parameters, Vmax and Km. Reaction rate was well monitored by capillary electrophoresis using the micellar electrokinetic chromatographic mode. Stereospecific reaction pattern of the enzyme was clearly solved for the synthesized substrates, RArSO.Three preparative methods to obtain optically pure sulfoxides were examined : (1) reduction by in vitro enzyme reaction which requires pure enzymes ; (2) biotransformation by adding substrates to the culture of Rhodobacter sphaeroides in which DMSO-R was beforehand induced and (3) reduction in bioreactor using immobilized DMSO-R.MTSO and methyltolylsulfoxide (MTSO) which are important intermediates for the asymmetric organic synthesis were applied to the method (2) and optically pure (R) isomers were obtained in gram-order yield.