Catechin-based flavones

Two classes of dimeric anthocyanins isolated from plants (section 10.2.6) have been identified in plants for the first time. One class includes pigments where an anthocyanin and a flavone or flavonol are linked to each end of a dicarboxylic acyl unit. The other class includes four different catechins linked covalently to pelargonidin 3-glucoside. During the last decade, seven new desoxyanthocyanidins and a novel type of anthocyanidin called P)Tanoanthocyanidins have been reported (Section 10.2.2). Toward the end of the 20th century, several color-stable 4-substituted anthocyanins, pyranoanthocyanins, were discovered in small amounts in red wine and grape pomace.Recently, similar compounds have been isolated from extracts of petals of Rosa hybrida cv. M me Violet, scales of red onion, and strawberries. About 94% of the new anthocyanins in the period of this review are based on only six anthocyanidins (Table 10.2). 

Unlike some classes of polyphenols such as flavonols and flavones, flavanols are almost always present in the nonglycosylated form. Removal of glycoside from flavonoids, usually necessary before the transport across the intestinal barrier, is not required in the case of flavanols [Scalbert and Williamson, 2000]. The absorption of procyanidins by the small intestine was investigated by studying 14C-( + )-catechin, dimer, trimer, and procyanidin polymers permeation through Caco-2 cell cultures [Deprez et al., 2001]. There was little difference in permeability between monomer, dimmer, and trimer, based on the measurement of radioactivity present on the basal side of the cultures, whereas the permeability of the polymers was 10 times lower. The authors reported the absence of catechin metabolism but did not determine whether the radioactivity measured on the basal side of the cultures was from the parent dimers to polymers or from their products of degradation or metabolites, which could have resulted from instability of the parent compounds in the culture... 

The catechins, and probably the leuco-anthocyanins (whose structure is not completely known) are derived from a reduced flavone, i.e., a flavan molecule catechins, e.g., catechin (VII), being flavan-3-ols. Anthocyanins, in the colored anionic form in which they usually occur, are flavylium salts e.g., cyanidin, VTII). The anthocyanins may, however, occur in a colorless form, known as a pseudo base, possibly (IX),... 

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