Isoflavones, occurrence

While fiavonoids have the 2-phenylchromen-4-one backbone, isoflavonoids (Fig. 8) have the 3-phenylchromen-4-one backbone, with no hydroxyl substitution at position 2 in the case of isofiavones. In contrast with the parent class of fiavonoids, the distribution of the isoflavonoid class in the plant kingdom is relatively limited, probably owing to the sporadic occurrence of isoflavone synthase. Isoflavonoids... 

Figure 7.11 (Continued) (f) Occurrence of flavonoids. Key to branches leading to families that accumulate isoflavones isoflavones and pterocarpans catechins/ proanthocyanins. See also legend (a).

Flavonoids are ubiquitous in all terrestrial plants (except the Anthoceropsidae) but the distribution of isoflavonoids among plants is relatively sparse, probably owing to the sporadic occurrence of the enzyme isoflavone synthasa that stabilises, by an aryl migration, the isoflavonoid skeleton. Accordingly, most of the isoflavonoids have been isolated from leguminous plants [3]. 

Kinoshita, T, T. Saitoh, and S. Shibata Chemical Studies on the Oriental Plant Drugs. 40. The Occurrence of an Isoflavene and the Corresponding Isoflavone in Licorice Root. Chem. Pharm. Bull. (Japan), 24, 991 (1976). 

Table 60.3 i Occurrence of isoflavones in leguminous and non-leguminous plants ... 

There are reports on the presence of isoflavonoids in numerous families of the plant kingdom inclusive 49 angiosperm families (Mackova et al. 2006). The most famous example is their occurrence in the Fabaceae. Isoflavones are formed by structural... 

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