The catalytic activity of mycelial fungi towards 7‐oxo‐DHEA – an endogenous derivative of steroidal hormone dehydroepiandrosterone

Seventeen species of fungi belonging to thirteen genera were screened for the ability to carry out the transformation of 7‐oxo‐DHEA (7‐oxo‐dehydroepiandrosterone). Some strains expressed new patterns of catalytic activity towards the substrate, namely 16β‐hydroxylation (Laetiporus sulphureus AM498), Baeyer–Villiger oxidation of ketone in D‐ring to lactone (Fusicoccum amygdali AM258) and esterification of the 3β‐hydroxy group (Spicaria divaricata AM423). The majority of examined strains were able to reduce the 17‐oxo group of the substrate to form 3β,17β‐dihydroxy‐androst‐5‐en‐7‐one. The highest activity was reached with Armillaria mellea AM296 and Ascosphaera apis AM496 for which complete conversion of the starting material was achieved, and the resulting 17β‐alcohol was the sole reaction product. Two strains of tested fungi were also capable of stereospecific reduction of the conjugated 7‐keto group leading to 7β‐hydroxy‐DHEA (Inonotus radiatus AM70) or a mixture of 3β,7α,17β‐trihydroxy‐androst‐5‐ene and 3β,7β,17β‐trihydroxy‐androst‐5‐ene (Piptoporus betulinus AM39). The structures of new metabolites were confirmed by MS and NMR analysis. They were also examined for their cholinesterase inhibitory activity in an enzymatic‐based assay in vitro test.