Coumarin metabolic routes in Aspergillus spp.

Coumarin metabolism by several Aspergillus strains was studied. Aspergillus ochraceus and Aspergillus niger carried out the reduction of the C3–C4 double bond to yield dihydrocoumarin in 24 h. Meanwhile, the first strain did not transform dihydrocoumarin after 7 d, A. niger demonstrated to have two divergent catabolic pathways: (a) the lactone moiety opening and further reduction of the carboxylic acid furnishing the primary alcohol 2-(3-hydroxypropyl)phenol and, (b) the hydroxylation of the aromatic ring of dihydrocoumarin at a specific position to give 6-hydroxy-3,4-dihydrochromen-2-one. Aspergillus flavus did not perform double bond reductions, and only produced oxygenated metabolites, mainly 5-hydroxycoumarin. Enzyme-specific inhibitors and a coumarin analogous were useful to confirm the A. niger catabolic route.