ABSTRACT
The isoflavones, of which upwards of 900-1000 examples have now been reported, are the most numerous and hence most commonly encountered of the many different types of isoflavonoid, the vast majority of which are only associated with species belonging to the subfamily Papilionoideae of the Leguminosae (Ingham, 1983). In some legumes, isoflavones with 2′- hydroxylation may be produced, a feature which allows these compounds to undergo cyclization to give comparatively rare isoflavonoids such as the pterocarpans, pterocarpenes and coumestans. Although isoflavones may occur in plants as free aglycones, it is not uncommon to find them combined with one or more sugars (notably glucose) as either O-or C-glycosides in which the sugar residue is connected to one or other of the aromatic rings via an ether link (as in O-glucosides such as daidzin 3 and genistin 4) or, much less frequently, by a direct C-C bond (as in C-glycosides). These sugar units may in turn be substituted at the 6′′ position with other sugars, or with acyl (e.g. acetyl) groups.
