The biocatalytic aerobic \"in-water\" reduction of anthranilic acid to 2-aminobenzaldehyde by growing cultures of the basidiomycetous white-rot fungus Bjerkandera adusta has been studied. The high specific activity of Bjerkandera adusta towards the carboxylic group of anthranilic acid that allows avoiding the formation of the corresponding alcohol has been demonstrated using different substrate concentrations. The presence of ethanol as co-solvent allows increasing the yield of target product. In contrast to chemical reducing agents that usually yield 2-aminobenzyl alcohol, an overreduction of anthranilic acid is completely suppressed by the fungus and gives the target flavor compound in satisfactory preparative yields. It was shown that the activity of Bjerkandera adusta towards anthranilic acid does not apply to its m- and p-isomers.

Since the first discovery of old yellow enzyme 1 (OYE1) from Saccharomyces pastorianus in 1932, biocatalytic asymmetric reduction of activated alkenes by OYEs has become a valuable reaction in organic synthesis. To access stereocomplementary C=C-bond bioreduction, the mining of novel OYEs and especially the protein engineering of existing OYEs have been performed, which successfully achieved the stereocomplementary reduction in several cases and further raise the potential of applications. In this review, we analyzed the structures, active sites, and substrate recognition of OYEs, which are the bases for their substrate specificity and stereospecificity. Sequence similarity network of OYEs superfamily was also constructed to investigate the scope of characterized OYEs. The structure-guided engineering to switch the stereoselectivity of OYEs and thus access stereocomplementary bioreduction over the last decade (2009-2020) was then reviewed and discussed, which might give new insights into the mining and engineering of related biocatalysts. KEY POINTS: • The sequence similarity network of OYEs superfamily was constructed and annotated. • The structures and active sites of OYEs from different classes were compared. • \"Left/right\" binding mode was used to explain the stereopreferences of OYEs. • Structure-guided engineering of OYEs to switch their stereoselectivity was reviewed.