Flavones, occurrence

PyrogaHol (1) was first observed by Scheele in 1786 as a product of the dry distillation of gaUic acid [149-91-7] (3,4,5-ttihydroxybenzoic acid). PyrogaHol, which is of widespread occurrence in nature, is incorporated in tannins, anthocyanins, flavones, and alkaloids (1). 

Kojic acid — see also Pyran-4-one, 5-hydroxy-2-hydroxymethyl-, 3, 611 acylation, 3, 697 application, 3, 880 occurrence, 3, 692 reactions, 3, 714, 715 with amines, 3, 700 with phenylhydrazine, 3, 700 synthesis, 3, 810 Kokusagine occurrence, 4, 989 Kokusaginine occurrence, 4, 989 synthesis, 4, 990 Koopmans theorem, 2, 135 Kostanecki-Robinson reaction chromone and coumarin formation in, 3, 819-821 mechanism, 3, 820 flavones, 3, 819... 

Hollman PCH and Arts ICW. 2000. Flavonols, flavones and flavanols nature, occurrence and dietary burden. J SciFood Agric 80 1081-1093. 

The occurrence of the diester structures of the malonic acid moiety in natural anthocyanin pigments has so far been reported in pigments from flowers of Eichhornia crassipes and chive. Allium schoenoprasum, where the anthocyanin-flavone and anthocyanin-flavonol disubstituted malonate structures were exhibited, respectively (Figure 10.8 and Figure 10.9). In some anthocyanins from flowers of Anemone coronaria, malonic acid is esterified with galactose in one end and tartaryl in the other end. ... 

C-Linked aromatic substituents are reported to occur in aerial parts of Thymus hirtus along with one report on Chinese propolis.In aerial parts of some members of Asteraceae and Lamiaceae, flavones with a C-6-ketopyrano-substitution were reported (e.g., hosloppin, oppositin see Figure 12.4). These aromatic substituents are positioned at the 6-, and rarely, at the 8-position of ring A. They are all reported from aerial parts, but no reference is made to their possible occurrence as exudates constituents. 

Data on this type of flavonols are summarized in Table 12.4. In contrast to the corresponding flavones, the number and complexity of derivatives is smaller. This concerns particularly the formation of furano-, pyrano- and other cyclic flavonols. There is a remarkable number of 0-prenylated flavonols known to date, contrasting to only very few flavones exhibiting this substitution pattern (see Table 12.3). Similar trends have been earlier documented in the review of Barron and Ibrahim. The occurrence of a series of glycosides based on C-prenylated structures is considerable. This substitution trend concerns also some of the dihydroflavonols, thus indicating specific enzyme activities probably dependent on the presence of a 3-OH group. 

The occurrence of acylated flavones and flavonols still appears interesting enough to justify a short paragraph on this subject (for compilation see Table 12.5). Of the flavones, only three compounds are known to date, with one newly reported isobutyrate flavone from leaf exudates of Asarina procumbens (Scrophulariaceae). One further compound, the 5 -benzoate of 8,2, 5 -trihydroxyflavone, was isolated recently from the exudate of Primula palinuri (linuma and Wollenweber, unpublished). 

Ahmad, S., Natural occurrence of Tephrosia flavones. Phytochemistry, 25, 955, 1986. 

The concentration of 4-oxo-flavonoids depends on the plant, environmental conditions, the part of the plant consumed, the degree of ripeness as well as on the food processing. Flavonoids are preferentially located in the epidermis solubilized in the vacuolar sap (especially flavones and flavonols glycosides) or in the epicuticular zone [20]. More detailed information about the occurrence of the different compounds is given in each subchapter. 

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