Flavan

Sesquiterpenes and flavonoids (flavones, flavanones, flavanes) are two elasses of natural substan-ees which occur frequently in plants and whieh have 15 C atoms in their framework. The nine... 

NMR spectroscopy in investigation of flavan-3-ols and their derivatives 97KPS16. 

Im Phenyl-Kern mit elektronenliefernden Funktionen substituierte Flavane werden durch Lithiumalanat/Aluminumchlorid-Mischungen aufgespalten z.B.7 ... 

Six anthocyanidins are commonly found in plants and plant-derived foods and beverages pelargonidin, cyanidin, delphinidin, peonidin, petunidin, and malvidin. Their structures differ in the number and position of hydroxyl and methoxyl groups on the flavan nucleus. The most commonly occurring anthocyanidin is cyanidin, and all these anthocyanidins are found in plants as glycosides with or without acylation, leading to around 400 different stractures. 

The effects of catechin, epicatechin, procyanidin B2, caffeic acid, / -coumaric acid, myricetrin, and quercetrin on the color intensity and stability of malvidin 3-glucoside at a molar ratio of 1 1 under conditions similar to red wine were evaluated. " Flavan 3-ols appeared to have the lowest protective effects and flavonols the highest strong color changes were visually perceptible. " In the complexation of malvin chloride and natural polyphenols, flavonol glycosides by far exerted the best protector effect. ... 

Fossen, T., Rayyan, S., and Andersen, 0.M., Dimeric anthocyanins from strawberry (Fragaria ananassa) consisting of pelargonidin 3-glucoside covalently linked to four flavan-3-ols. Phytochemistry, 65, 1421, 2004. 

Many higher plants synthesize flavanes, flavanones, flavones, and isoflavones with a wide range of structural complexity. They make a significant contribution to the food intake of both herbivores and humans, and they have aroused particular interest on account of their degradation by mammals that are mediated by intestinal bacteria. Most of them exist naturally as glycosides and these are readily hydrolyzed to the aglycones. 

The B-type procyanidins include a mixture of oligomers and polymers composed of flavan-3-ol units linked mainly through C4 C8 and/or C4 C6 bonds, and represent the dominant class of natural proanthocyanidins. Among the dimers, procyanidins Bl, B2, B3 and B4 (Fig. 2a) are the most frequently occurring in plant tissues. Procyanidin B5 (EC-(4j6 6)-EC), B6 (catechin-(4o 6)-catechin), B7 (EC-(4/3 6)-catechin) and B8 (catechin-(4q 6)-EC) are also widespread (Eig. 2b) [17-19]. 

On the other hand, the flavan-3-ol units can also be doubly linked by an additional ether bond between C2 07 (A-type). Structural variations occurring in proanthocyanidin oligomers may also occur with the formation of a second interflavanoid bond by C-0 oxidative coupling to form A-type oligomers (Fig. 3) [17,20]. Due to the complexity of this conversion, A-type proanthocyanidins are not as frequently encountered in nature compared to the B-type oligomers. 

In a few cases, the synthesis was directed towards well-defined oligomers (dimers, trimers, etc.). The synthesis of bis(5,7,3, 4 -tetra-0-benzyl)-EC 4/1,8-dimer from 5,7,3, 4 -tetra-0-benzyl-EC and 5,7,3, 4 -tetra-0-benzyl-4-(2-hydroxyethoxy)-EC was described by Kozikowski et al. [41]. This compound exhibited the ability to inhibit the growth of several breast cancer cell fines through the induction of cell cycle arrest in the Gq/Gi phase. Analogously, procyanidin-B3, a condensed catechin dimer, has been obtained through condensation of benzylated catechin with various 4-0-alkylated flavan-3,4-diol derivatives in the presence of a Lewis acid. This reaction led to protected procyanidin-B3 and its diastereomer. In particular, octa-O-benzylated procyanidin-B3 has been produced with high levels of stereoselectivity and in excellent isolation yields [42]. 

Porter LJ (1993) Flavans and proanthocyanidins. In Harborne JB (ed) The Flavonoids Advances in Research Since 1986. Chapman Hall, London, p 23... 

Porter LJ (1988) Flavans and Proanthocyanidins. In Harborne JB (ed) The Fla-vanoids Advances in Research since 1980. Chapman Hall, New York, p 21... 

Feucht, W. and Treutter, D. (1999). The role of flavan-3-ols and proanthocyanidins in plant defense , in Inderjit, K. and Dakshini M.M F.C.L., Principles and Practices of Plant Ecology, CRC Press, London, 307-338. 

Flavan-3-ols orflavanols have a saturated three-carbon chain with a hydroxyl group in the C3 position. In foods they are present as monomers or as proanthocyanidins, which are polymeric flavanols (4 to 11 units) known also as condensed tannins. In foods they are never glycosylated. 

Food and plant phenolics are commonly detected using DAD detectors (Tan and others 2008). Photodiode array detection allows collection of the entire UV spectrum during the elution of a chromatographic peak, which makes it possible to identify a phenolic compound by its spectra. Simple phenols, phenolic acids, flavanones, benzophenones, isoflavones, and flavan-3-ols have maximum absorbance at 280 nm, hydroxycinnamic acids at 320 nm, flavonols, flavones, and dihydroflavonols at 365 nm, and anthocyanins at 520 nm (Ibern-G6mez and others 2002 Merken Hand Beecher 2000). Hydrolyzable tannins show a characteristic shoulder at 300 nm, suitable for identifying them (Arapitsas and others 2007). For stilbenes, maximum absorbance of trans-forms are at 306 nm and at 285 nm for cA-forms (Lamuela-Raventos and others 1995). 

Flavan-3-ols Catechin Peaches Berries Red grape Bananas... 

Proanthocyanidins (PAs), also known as condensed tannins, are oligomeric and polymeric flavan-3-ols. Procyanidins are the main PAs in foods however, prodelphinidins and propelargonidins have also been identified (Gu and others 2004). The main food sources of total PAs are cinnamon, 8084 mg/100 g FW, and sorghum, 3937 mg/100 g FW. Other important sources of PAs are beans, red wine, nuts, and chocolate, their content ranging between 180 and 300 mg/100 g FW. In fruits, berries and plums are the major sources, with 213.6 and 199.9 mg/100 g FW, respectively. Apples and grapes are intermediate sources of PAs (60 to 90 mg/100 g FW), and the content of PAs in other fruits is less than 40 mg/100 g FW. In the majority of vegetables PAs are not detected, but they can be found in small concentrations in Indian squash (14.8 mg/ 100 g FW) (Gu and others, 2004 US Department of Agriculture, 2004). 

Polster J, Dithmar H and Walter F. 2003. Are histones the targets for flavan-3-ols (catechins) in nuclei Biol Chem 384(7) 997-1006. 

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