High operational stability in peroxidase-catalyzed non-aqueous sulfoxidations by encapsulation within sol–gel glasses

The peroxidase activity of immobilized horseradish peroxidase (HRP) has been employed for the asymmetric oxidation of thioanisole in acetonitrile with H2O2 (30%). Encapsulation of HRP by the sol–gel method considerably enhanced its operational stability by protecting the peroxidase activity under harsh conditions. The total rates of the encapsulated HRP increased up to six-fold (TTN=4.22×103) the rates observed with its homogeneous counterpart. The sulfoxide selectivity and the enantiomeric excess also increased greatly upon encapsulation. Coupling glucose oxidase reaction to the encapsulated peroxidase allowed high enantiomeric excesses (up to 56%) and sulfoxide as sole product by elimination of side non-enantioselective and overoxidation reactions. The heterogeneous catalyst can be recycled by simple filtration in successive runs.