Enantioselective sulfoxidations catalyzed by horseradish peroxidase, manganese peroxidase, and myeloperoxidase

Horseradish peroxidase (HRP), myeloperoxidase (MPO), and manganese peroxida se (MnP) have been shown to catalyze the asymmetric sulfoxidation of thioan isole. When H2O2 was added stepwise to MPO, a maximal yield of 78% was obta ined at pH 5 (ee 23%), whereas an optimum in the enantiomeric excess (32%, (R)-sulfoxide) was found at pH 6 (60% yield). For MnP a yield of 18% and a high enantiomeric excess of 91% of the (S)-sulfoxide were obtained at pH 5 and a yield of 36% and an ee of 87% at pH 7.0. Optimization of the conversi on catalyzed by horseradish peroxidase at pH 7.0 by controlled continuous a ddition of hydrogen peroxide during turnover and monitoring the presence of native enzyme as well as of intermediates I, II, and III led to the format ion of the sulfoxide in high yield (100%) and moderate enantioselectivity ( 60%, (S)-sulfoxide).