Isomerization isoflavones

Flavonoids can be classified according to their biosynthetic origins. Some flavonoids are both intermediates in biosynthesis and end-products, e.g. chalcones, flavanones, flavanon-3-ols and flavan-3,4-diols. Other classes are only known as the end-products of biosynthesis, e.g. anthocyanins, flavones and flavonols. Two further classes of flavonoids are those in which the 2-phenyl side-chain of flavonoid isomerizes to the 3-position (giving rise to isoflavones and related isoflavonoids) and then to the 4-position (giving rise to the neoflavonoids). The major classes of flavonoids, with specific examples, are summarized helow. 

The reactions of arylation of heterocyclic /3-ketoesters were employed in the synthesis of a number of isoflavanones and isoflavones.27,28 cr-Methylene cr-arylketones can be easily and selectively obtained by arylation of allyl /3-ketoesters which are eventually deprotected by the Tsuji s procedures. a Deallyloxycarbonylation was performed by treatment of the allyl cr-aryl-/3-ketoesters with catalytic amounts of palladium(n) acetate, triethylammo-nium formate and triphenylphosphane in THF at room temperature and afforded the a-arylketones in 75-97% yield.27 Deallyloxycarbonylation-dehydrogenation can be realized with the same allyl esters by treatment with catalytic amounts of palladium(n) acetate and l,2-bis(diphenylphosphino)ethane (DPPE) in acetonitrile under reflux and affords the ct-aryl cr,/3-unsaturated ketones in 60-90% yield (Scheme 4).28 In particular, this reaction was used in a direct convergent synthesis of 2 -hydroxyisoflavones involving arylation of an appropriate allyl /3-ketoester with the MOM-protected (2-methoxymethoxyphenyl)lead triacetate derivative (Scheme 4). The reaction of the isomeric... 

Losses of small molecules and/or radicals from [M+H]" are observed in the positive-ion mode losses of HjO, CO, and HjC=C=0, and combinations thereof. The loss of a methyl radical CHj is characteristic for O-methylated isoflavones, flavones, and flavonols [13]. Loss of C4H8 indicates the presence of prenyl substituents (at 3-, 6-, and/or 8-position) [t4]. Kuhn et al. [t5] demonstrated the differentiation between isomeric flavones and isoflavones by means of positive-ion MS-MS in an ion-trap instmment. tsoflavones show an abundant fragment ion due to the loss of 2 CO molecules from the C-ring, while flavones only show a single CO loss. 

F. Kuhn, M. Oehme, F. Romero, E. Abou-Mansour, R. Tabacchi, Differentiation of isomeric flavone/isoflavone aglycones by ion trap MS and a double neutral loss of CO, Rapid Commun. Mass Spectrom., 17 (2003) 1941. 

While flavans are quite rare in nature, the isomeric isoflavans are more numerous (there are 39 of them), and they occur fairly widely, at least in members of the Leguminosae. Isoflavans are optically active and compounds with both the R-and 5- configuration at C-3 have been described. Two typical isoflavans are equol (49) which occurs in the heartwood of Millettia pendula but is better known as a urinary metabolite in mammals of the isoflavone formononetin (109) and (-)-duartin (50) present in the heartwood of several Machaerium species. Isoflavans (and pterocarpans) occur in a different context than wood chemistry in the... 

West, L.G., Birac, P.M., and Pratt, D.E., Separation of the isomeric isoflavones from soybeans by high-performance liquid chromatography, J. Chromatogr., 150, 266, 1978. 

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