Biocatalytic oxidation of alcohols using galactose oxidase and a manganese(iii) activator for the synthesis of islatravir

Abstract

Galactose oxidase (GOase) is a Cu-dependent metalloenzyme that catalyzes the oxidation of alcohols to aldehydes. An evolved GOase variant was recently shown to catalyze a desymmetrizing oxidation as the first enzymatic step in the biocatalytic synthesis of islatravir. Horseradish peroxidase (HRP) is required to activate the GOase, introducing cost and protein burden to the process. Herein we describe that complexes of earth-abundant Mn(III) (e.g. Mn(OAc)₃) can be used at low loadings (2 mol%) as small molecule alternatives to HRP, providing similar yields and purity profiles. While an induction period is observed when using Mn(OAc)₃ as the activator, employment of alternative Mn(III) sources, such as Mn(acac)₃ and K₃[Mn(C₂O₄)₃], eliminates the induction period and provides higher conversions to product. We demonstrate that use of the Mn(OAc)₃ additive is also compatible with subsequent biocatalytic steps in the islatravir-forming cascade. Finally, to exhibit the wider utility of Mn(OAc)₃, we show that Mn(OAc)₃ functions as a suitable activator for several commercially available variants of GOase with a series of alcohol substrates.