Chloroperoxidase catalyzed oxidations in t-butyl alcohol/water mixtures

Abstract Chloroperoxidase catalyzed oxidations of sulfides and indoles were performed in t -butyl alcohol/water mixtures at ambient temperature. t -Butyl alcohol/water (50:50, v/v) proved to be a good solvent system for performing synthetic oxidations catalyzed by chloroperoxidase. The sulfoxidation of alkyl aryl sulfides and related compounds catalyzed by chloroperoxidase in t -butyl alcohol/water mixtures (50:50, v/v) was compared to the sulfoxidation in water. In both solvent systems, complete enantioselectivity to the R -sulfoxide (ee = 99%) was observed with hydrogen peroxide as oxidant when the size of the alkyl moiety was smaller than propyl. The uncatalyzed, racemic sulfoxidation did not proceed under these conditions. This is in contrast to literature data on sulfoxidation in water, where enantioselectivities were lower due to this uncatalyzed reaction. Reactions in water generally proceed faster than reactions in the cosolvent system except for substrates which dissolve poorly in water or for solid substrates for which diffusion becomes an important limiting factor in water. The lower activity in t -butyl alcohol/water for sulfoxidation and for indole oxidation is mainly due to an increase of the K m value (thermodynamically controlled). Also a decrease of k cat (catalytic turnover frequency) is observed, probably caused by a change in structure of the enzyme.