Enantioselective sulfoxidation catalyzed by vanadium haloperoxidases

Vanadium haloperoxidases catalyze the oxidation of halides by hydrogen pero xide to produce hypohalous acid. We demonstrate that these enzymes also slo wly mediate the enantioselective oxidation of organic sulfides (methyl phen yl sulfide, methyl p-tolyl sulfide, and 1-methoxy-4 (methylthio)benzene) to the corresponding sulfoxides (turnover frequency 1 min(-1)). The vanadium bromoperoxidase from the brown seaweed Ascophyllum nodosum converts methyl phenyl sulfide to the (R)-enantiomer of the sulfoxide (55% yield and 85% en antiomeric excess (ee)). At low peroxide concentrations a selectivity of 91 % can be attained. The enzyme catalyzes the selective sulfoxidation reactio n over a broad pH range with an optimum around pH 5-6 and remains completel y functional during the reaction. When the vanadium bromoperoxidase from th e red seaweed Corallina pilulifera is used the (S)-enantiomer (18% yield an d 55% ee) is formed. In contrast, the vanadium chloroperoxidase from the fu ngus Curvularia inaequalis catalyzes the production of a racemic mixture (5 4% yield), which seems to be an intrinsic characteristic of this enzyme.