Biocatalysis has become a mature technology for many synthetic applications. In this discipline, the use of enzymes in non-aqueous environments (so-called 'non-conventional' media) has attracted considerable attention during the last years, as high substrate loadings, volumetric productivities and product titers may be achievable, enabling practical outcomes. The use of hydrolases in non-aqueous media is an established approach already proven at industrial scale. Surprisingly oxidoreductases - which catalyze synthetically interesting reduction-oxidation reactions - have been limitedly applied in low-water-content conditions until very recently. This review focuses on the recent achievements in applying oxidoreductases in non-conventional media namely, use of neat-substrates, organic solvents and deep eutectic solvents, with critical emphasis on the opportunities and current challenges of those strategies.
