The present review focuses on the fungal metabolism of different classes of naturally occurring flavonoidal fungitoxins, i.e., simple and prenylated flavonoids (flavones, flavonols and flavanones), and isoflavonoids (isoflavones, isoflavanones, pterocarpans and rotenoids). Many kinds of phytopathogenic and some non-pathogenic fungi have been used for metabolic studies of constitutive and induced flavonoidal and related fungitoxins, prohibitins and phytoalexins. As with other plant secondary metabolites, flavonoids are also metabolized by diverse species of fungi through modifications of the functional groups and decomposition of the characteristic skeletons in the substrates. Fungal transformation of prenylated flavonoids and isoflavonoids into the corresponding metabolites possessing glycol-, dihydrofurano- and dihydropyrano-side attachments via an epoxide intermediate is stressed, because the metabolic pathway including the stereochemistry and the catalyzing enzyme has been relatively well established and revealed that the sequential processes partly resemble those found in the plant secondary metabolism. Since almost all of fungal metabolism of plant originated fungitoxins recognized as defense substances produces more polar and less toxic metabolites than the substrates, the process is therefore, termed as detoxification which is believed to be closely related to the compatibility between the plant and its pathogen. Therefore, the present topic is also interested in a trait of phytopathology. Rare examples for fungal glycosylation of flavones and chlorination of isoflavones are also referred.
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