Application of Basidiomycota-derived biocatalysts in organic synthesis

Abstract

The increasing demand for sustainable and selective methods of organic synthesis drives the replacement of traditional energy-intensive processes often based on toxic chemical reagents. Biocatalysis offers an attractive alternative that allows efficient transformations to be carried out under mild and environmentally friendly conditions. White-rot fungi represent a particularly promising source of such biocatalysts, as approaches based on these fungi exhibit high enzyme stability and unique enzymatic pathways compared to other biocatalytic methods based on bacteria or yeasts. Their non-toxic nature, along with straightforward application and accessibility, makes them attractive for various biotechnological processes. Nevertheless, the practical application of fungi as biocatalysts, including both growing cultures and storable lyophilized mycelium, remains insufficiently explored in preparative organic synthesis. The present dissertation focuses on the disclosing of biocatalytic potential of the white-rot fungus Bjerkandera adusta, chosen for its non-toxic nature, rich enzymatic profile, and simple cultivation on inexpensive substrates. The work investigates the biocatalytic potential of both, the growing culture and the lyophilized mycelium with the aim of developing practical, selective, and green preparative approaches for the transformation of organic compounds. Particular attention is given to the ability of B. adusta to carry out oxidation and reduction reactions under mild and environmentally friendly conditions. Lyophilized mycelium of B. adusta was shown to catalyze clean and selective oxidations of aromatic alcohols to the corresponding aldehydes under “on-water-on-air” conditions. The catalytic activity observed in the lyophilized mycelium was shown to be associated with the presence of aryl-alcohol oxidases. High conversion rates without overoxidation were achieved under mild conditions, and the lyophilisate retained its oxidative activity over extended storage periods, highlighting its practical value for further applications. The oxidative potential of the lyophilisate of B. adusta was further demonstrated through the selective conversion of α,β-unsaturatedalcohols into valuable (E)-allylic aldehydes. The addition of small amounts of organic co-solvents enhanced substrate conversion while maintaining high chemoselectivity. Notably, B. adusta also mediated the isomerization of (Z)-2-nonenal to the corresponding (E)-diastereomer without further carbonyl group oxidation or CC-double bond reduction, which is rarely achieved under such conditions. Comparative experiments with lyophilisates of Pleurotus species confirmed the special catalytic efficiency of B. adusta in these reactions. In contrast, growing cultures of B. adusta exhibited reductive activity, selectively converting anthranilic acid into 2-aminobenzaldehyde while completely suppressing overreduction to the corresponding alcohol. This transformation proceeds in aqueous aerobic conditions and displays strict regioselectivity, with only the o-isomer accepted as a substrate.