Flavonoids difference from isoflavonoids

In contrast to the almost ubiquitous occurrence of the flavonoids in higher plants, the isoflavonoids have a very limited taxonomic distribution. They are in general confined to one group of plants - the sub-family Lotoideae of the Leguminosae [390, 391 ]. Occasionally they occur in a few other families [326], The overall biological properties also differ from those of the flavonoids flavonoids on the whole are innocuous substances [392], but isoflavonoids usually have oestrogenic, insecticidal, piscicidal and/or antifungal activities. 

It has already been noted that there is a considerable structural variation among isoflavonoids and at least three other structural types are represented in the genus Cicer. Note that the numbering systems for these variants differ from each other. Isoflav-3-enes conform to the usual flavonoids numbering system but coumestanes and arylbenzofurans are different. 

Polyphenols include flavonoids, proanthocyanidins, stilbenes, microbial metabolites of lignan, and hydroxycinnamates (Fig. 2). Flavonoid metabolism, while still far from being fully understood, has been the most widely studied and will therefore form the basis of this chapter. Six main subclasses of flavonoids are widely consumed by humans flavonols, flavones, flavanones, isoflavonoids, flavanols (catechins), and anthocyanins these posses the generic structure shown in Fig. 3. These classes differ in the degree of saturation and the nature and position of reactive groups on their three rings examples of substitution patterns for selected flavonoids are given in Table 1. 

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