Metabolism of the Prenylated Pterocarpan Edunol by Aspergillus flavus

In our previous papers, we reported that isoflavones with a 3,3-dimethylallyl (prenyl) substituent at C-6, C-8 (ring A) or C-3' (ring B) were variously metabolized by the fungus Aspergillus flavus to give hydrates (luteone [1] and wighteone [2]), and deri­ vatives possessing dihydrofurano, dihydropyrano or 2,3-dihydrodihydroxyprenyl side-attachments (luteone [1], wighteone [2], 2,3-dehydrokievitone [3], licoisoflavone A [4], and 2'-hydroxylupalbigenin [5]). Studies involving the plant pathogenic fungus Fusarium oxysporum f. sp. phaseoli have shown that two other prenylated isoflavonoids, kievitone [5,7,2',4'-tetrahydroxy-8-(3,3-dimethylallyl)isoflavanone] and phaseollidin [3,9-dihydroxy-10-(3,3-dimethylallyl)pterocarpan] are also metabolized in vitro to give the corresponding hydrates [6, 7]. In kievitone and phaseollidin, the prenyl groups are lo­ cated on different aromatic rings, and their hydration by F. oxysporum f. sp. phaseoli suggests that the enzyme responsible (kievitone hydratase [8]) is rel­ atively non-specific in its action, or the fungus con­ tains two hydratases differing in the substrate specificity [9], In contrast, A. flavus exhibits a higher degree of substrate preference bringing about hydration of pre­ nyl groups at C-6 on ring A of isoflavones (luteone and wighteone [1, 2], but not those located at C-8 (also ring A; 2,3-dehydrokievitone [3]) or C-3' (ring B; licoisoflavone A and 2'-hydroxylupalbigenin [4,