Flavan catechin

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. ... 

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]. 

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]. 

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

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. 

Flavanols and procyanidins Flavanols, or flavan-3-ols, are synthesized via two routes, with (+) catechins formed from flavan-3,4-diols via leucoanthocyanidin reductase (LAR), and (—) epicatechins from anthocyanidins via anthocyanidin reductase (ANR) (see Fig. 5.4). These flavan-3-ol molecules are then polymerized to condensed tannins (proanthocyanidins or procyanidins), widely varying in the number and nature of their component monomers and linkages (Aron and Kennedy 2008 Deluc and others 2008). It is still not known whether these polymerization reactions happen spontaneously, are enzyme catalyzed, or result from a mixture of both. 

Flavan-3,4-diols FIavan-3,4-diols, also known as leucoanthocyanidins, are not particularly prevalent in the plant kingdom, instead being themselves precursors of flavan-3-ols (catechins), anthocyanidins, and condensed tannins (proanthocyanidins) (see Fig. 5.4). Flavan-3,4-diols are synthesized from dihydroflavonol precursors by the enzyme dihydroflavonol 4-reductase (DFR), through an NADPH-dependent reaction (Anderson and Markham 2006). The substrate binding affinity of DFR is paramount in determining which types of downstream anthocyanins are synthesized, with many fruits and flowers unable to synthesize pelargonidin type anthocyanins, because their particular DFR enzymes cannot accept dihydrokaempferol as a substrate (Anderson and Markham 2006). 

Flavonoids are a complex group of polyphenolic compounds with a basic C6-C3-C6 structure that can be divided in different groups flavonols, flavones, flavanols (or flavan-3-ols), flavanones, anthocyanidins, and isoflavones. More than 6,000 flavonoids are known the most widespread are flavonols, such as quercetin flavones, such as lu-teolin and flavanols (flavan-3-ols), such as catechin. Anthocyanidins are also bioactive flavonoids they are water-soluble vegetable pigments found especially in berries and other red-blue fruits and vegetables. 

Condensed or catechin tannins (catechol tannins. Fig. 11.3) are the most common tannins in vascular plants, occurring in three quarters of gym-nosperms and over half of the angiosperms. They are unbranched, linear polymers of flavonoid compounds (flavan-3-ols), linked through acid-labile carbon-carbon bonds. Condensed tannins may protect plant cell walls against microbial attack and so may affect microbial fermentation of plant cell walls in herbivores. 

FIGURE 11.3 Condensed tannin. Catechin, a flavan-3-ol, is one of the most common building blocks. 

Assuming the former to be the case, we considered that the LHR inducers might be more polar in nature and were therefore excluded by separatory techniques for compounds such as those known to induce WHR A. tumefa-ciens. Proanthocyanidin monomers (i.e., catechins, flavan-3-ols), oligomers,... 

Repeated TLC of active, pooled fractions from Red Flame grapes revealed major spots with Ry s corresponding to those of catechin and epi-catechin, identical color reaction with p-toluenesolfonic acid spray reagent, and coelution of trimethylsilane (TMS) derivatives by GC with reference samples of these flavans. However catechin and epicatechin were assayed with the bacterial strains described and no activity was detected. TMS-derivatized samples of active grape flavans were examined by GC-MS, but a search for the molecular ions of a number of known wr-inducing phenolics yielded negative results. 

Gas Chromatography. In our GC analyses, N,0-bis-(Trimethylsilyl) Trifluo-roacetamide (BSTFA)-derivatized standards of known wtr-inducing pheno-lics failed to correspond in retention time to any of the derivatized samples of the most active grape flavan fractions. Catechin and epicatechin were tentatively identified by GC. 

Flavan-3-ols (catechins, proanthocyanidins, and condensed tannins) can often be extracted directly with water. However, the composition of the extract does vary with the solvent — whether water, methanol, ethanol, acetone, or ethyl acetate. For example, it is claimed that methanol is the best solvent for catechins and 70% acetone for procyanidins. ... 

Notes The chirality of C-3 on the flavan-3-ols cannot be differentiated by MS. (Epi)afzelechin represents either afzelechin or epiafzelechin. Afz, afzelechin Cat, catechin A, A-type binding between the flavanol units, i.e., flavanols doubly linked by an additional ether bond between C-2 and 0-7 in addition to the C4-C8 (or more rarely C4-C6) bond. 

LAR removes the 4-hydroxyl from leucoanthocyanidins to produce the corresponding 2,3-tran5-flavan-3-ols, e.g., catechin from leucocyanidin. Despite early biochemical characterization, it is only recently that a LAR cDNA was isolated and the encoded activity characterized in detail. Tanner et al. purified LAR to homogeneity from Desmodium uncinatum (silverleaf desmodium), and used a partial amino acid sequence to isolate a LAR cDNA. The cDNA was expressed in E. coli, N. tabacum, and Trifolium repens (white clover), with the transgenic plants showing significantly higher levels of LAR activity than nontransformed plants. 

Monitoring of acetaldehyde-induced polymerization of catechin and epicatechin by HPLC-MS demonstrated the formation of several methylmethine-linked flavanol dimers, trimers, and tetramers. Detection of the intermediate ethanol adducts confirmed the mechanism postulated by Timberlake and Bridle, which involves protonation of acetaldehyde in the acidic medium, followed by nucleophilic attack of the resulting carbocation by the flavan unit. The ethanol adduct then loses a water molecule and gives a new carbocation that undergoes nucleophilic attack by another flavanol molecule. Four dimers (C6-C6, C8-C8, and C6-C8, R and S) were formed from each monomeric flavanol. When both epicatechin and catechin units were present, additional isomers containing both types of units were... 

---