Isoflavonoid aglycones

FIGURE 7.2 Chemical structures of the main soy (genistein and daidzein) and red clover (biochanin A and formononetin) isoflavonoids (aglycones and glucosides). 

Protein engineering has been utilized to study the mechanism by which isoflavonoid aglycones are converted to isoflavonoid glycosides by uridine diphosphate glycosyltransferases, a large protein class catalyzing the transfer of activated... 

Fig. 60.4 Structure of the isoflavonoid aglycones, formononetin, biochanin A, and glycitein...

Based on isoflavonoid aglycones published as new in this period. 

Recently, some of the specific faecal bacteria involved in the metabolism of dietary isoflavonoids were isolated (Hur et al., 2000). They have been shown to selectively convert genistin and daidzin to their respective aglycones. One of the isolated bacteria, under anoxic conditions, was further shown to metabolise genistein and daidzein to their respective dihydroxy-genistein and dihydroxy-daidzein. In the case of lignans, enterodiol and enterolactone were shown to be excreted in vivo only in rats harbouring a gut microflora (Rowland et al, 1999). 

In three of the volumes of The Flavonoids, Advances in Research, published between 1975 and 1993, flavanones and dihydroflavonols were part of the chapter on Minor Flavonoids, expertly written by Professor Bruce Bohm. These Minor Flavonoid chapters also included chalcones, dihydrochalcones, and aurones. The term Minor Flavonoids was first used by Harborne in 1967 to encompass not only flavanones, chalcones, and aurones, but also isoflavonoids, biflavonyls, and leucoanthocyanidins, because so few compounds belonging to each of these flavonoid classes were known at that time. For example, only about 30 flavanone and dihydroflavonol aglycones, 19 chalcones, and 7 aurones were known in 1967. The number of known minor flavonoids increased considerably in the next two decades, so that when the checklist for The Flavonoids, Advances in Research Since 1980 was published in 1988, 429 known flavanones and dihydroflavonols (including glycosides) were listed, 268 chalcones and dihydrochalcones, and 29 aurones. In the last 15 years, the total number of known compounds in these flavonoid classes has more than doubled, so that the term minor flavonoids is no longer appropriate. Consequently, it has been decided that separate chapters should be devoted to the flavanones and dihydroflavonols (this chapter), and chalcones, dihydrochalcones, and aurones (Chapter 16). 

Isoflavonoids are also compounds that should be bom in mind for future cytotoxic studies with flavonoids. Isoflavones (aglycones with a 2-3 double bound, a 4 oxo group and the B-ring at C3 position) with the association of substituents mentioned above are not studied and could be. Besides, rotenoids are very cytotoxic isoflavonoids that are not well studied although one of them, 12a 3-hydroxyamorphigenin, is the most cytotoxic flavonoid found in our review, with values of less than 0.001 pg/mL on the six human cancer cell lines tested by Li et a/. [78]. 

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