Choline Oxidase and Choline Ionic Liquids in Biocatalytic Heme Peroxidase Cascades

Choline oxidase from Alcaligenes sp. (ChOx) is used to generate hydrogen peroxide in situ from choline-based ionic liquids (ILs) to fuel peroxidase-mediated biocatalysis while mitigating oxidative degradation of the heme-dependent enzymes. Horseradish peroxidase (HRP) and chloroperoxidase from Caldariomyces fumago (CPO), in combination with the ChOx, are evaluated in enzymatic cascades for the ability of the biocatalytic systems to withstand elevated concentrations of different choline additives in oxidative and halogenative enzymatic assays. The findings are applied in various synthetic scenarios to produce important oxygen- and nitrogen-containing heterocycles, using choline ILs in a dual-purpose fashion, as a substrate-solubilizing component in the reaction medium as well as the source for hydrogen peroxide. The ChOx/HRP couple is used to induce intramolecular cyclizations of hydroxamic acids and hydroxycarbamates in a nitroso-ene-type pathway with choline dihydrogen phosphate as IL additive. The ChOx/CPO cascade successfully mediates brominative cyclizations of alpha-allenic alcohols, while amphiphilic surfactants are employed to turn the aqueous choline propionate IL media into a colloidal suspension. ChOx/CPO partnering is also evaluated in an oxygenative rearrangement of 1-furylethanol with choline acetate IL. The results show the wide potential of choline oxidase for hydrogen peroxide-driven biocatalysis with both aqueous and micellar choline ionic liquid solutions.