Chloroperoxidase‐catalyzed enantioselective oxidations in hydrophobic organic media

Abstract

Chloroperoxidase from Caldariomyces fumago, a peroxidase that performs P450-like chemistry, was immobilized via covalent attachment into polyurethane foam as well as conjugated with a surfactant or polymer via colyophilization. The resulting preparations catalyzed enantio- and regioselective oxidations in hydrophobic organic media with tert-butyl hydroperoxide as the oxidant. Dried PUR-foam immobilized CPO mediated the selective oxidation of indole to 2-oxindole (regioselectivity: 99%) in water-saturated isooctane or 1-octanol. Thioanisole was converted into the corresponding (R)-sulfoxide (ee > 99%) in isooctane medium. The complexes of CPO with sodium octadecylsulphate or ethyl cellulose mediated the oxidation of thioanisole in water-immiscible organic media with variable enantioselectivity due to radical side-reactions. In the presence of alpha-tocopherol, acting as radical scavenger, the (R)-sulfoxide was formed with ee > 90%. The effect of the water activity on the catalytic activity of the complexes was investigated. The CPO complexes likewise mediated the regioselective oxidation of indole into 2-oxindole in water-saturated isooctane or 1-octanol and its kinetics were investigated. The reaction suffered from substrate inhibition when carried out in isooctane.