A Single Enzyme Oxidative “Cascade” via a Dual-Functional Galactose Oxidase

The galactose oxidase (GOase) M3-5 variant, previously engineered for enantioselective oxidation of (R)-secondary alcohols, is now shown to catalyze the sequential four-electron oxidation of substituted benzylic and heteroaromatic benzylic alcohols to the corresponding carboxylic acids via the intermediate aldehyde. Aldehyde oxidation has been shown to occur on the hydrated (gem-diol) form of the aldehyde, and hence the activity of this second oxidation step is primarily determined by the effects of substituents on the aromatic ring. The demonstration of GOase for "through oxidation" of alcohols to carboxylic acids represents a fusion of the activities of two distinct copper radical oxidases (galactose oxidase and glyoxal oxidase) into a single enzyme sequence with potential applications as an abbreviated oxidative cascade.