Flavan-3-ols epicatechin

Zhu QY, Holt RR, Lazarus SA, Ensunsa JL, Hammerstone JF, Schmitz HH, Keen CL. 2002. Stability of the flavan-3-ols epicatechin and catechin and related dimeric procyanidins derived from cocoa. J Agric Food Chem 50 1700-1705. 

Kubo, I. and Hanke, R (1986) A possible new role for the flavan-3-ol(-)-epicatechin in plants. Prog. Clin. Biol. Res., 213,101-12. 

The flavan-3-ols (-)-epicatechin (202 mg/kg) and (+)-catechin (44 mg/kg) have also been reported [19], while the flavonols, quercetin 3-rutinoside (the principal flavonol), and kaempferol 3 rutinoside, were only located in the skin at a concentration of 15 mg of flavonoids per kg of fruit [21 22]. 

In 1997, a flavan-3-ol (-)-epicatechin (1) was identified from the cell suspension cultures in the callus tissue cultures of Hypericum patulum (Figure... 

In apple (Malus domestica Borkh.), flavonoid biosynthetic pathway was engineered by introducing maize leaf color (Lc) regulatory gene [73]. Leaf tissue of Lc-transgenic lines had higher levels of anthocyanin idaein (12-fold), flavan 3-ol epicatechin (14-fold), isomeric catechin (41-fold), and dimeric proanthocyanidins (7- to 134-fold). 

In 2001, we demonstrated that pretreatment of primary striatal neurons with low-micromolar concentrations of the flavan-3-ol epicatechin and the flavonol kaempferol potently protected against Ox-LDL-induced neuronal apoptosis [177]. The neuronal death induced by Ox-LDL was characterized by a time- and dose-dependent decrease in MTT reduction and membrane integrity and increase in annexin-V binding, caspase-3-hke protease activity, and DNA fragmentation. In addition, it was demonstrated that oxLDL is a rapid activator... 

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. ... 

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. 

The synthetic protocol (Scheme 11.2) toward the flavan-3-ol permethylaryl ethers is based upon the transformation of rc7ro-chalcones into 1,3-diarylpropenes. These compounds are then subjected to asymmetric dihydroxylation to give diarylpropan-l,2-diols that are used as chirons for essentially enantiopure flavan-3-ols. The protocol is demonstrated in Scheme 11.2 for the synthesis of the tetra-(9-methyl-3-(9-acetyl derivatives 61a, 61b, 62a, and 62b of (-l-)-catechin (2), (—)-e 7-catechin, (—)-epicatechin (3), and (+)-e 7-epicatechin (4). ... 

Simultaneous deprotection and cyclization of diols 60a and 60b with 3 M HCl in MeOH followed by acetylation yielded the 2,3-trans- ( 50%) (61a and 61b) and for the first time 2,3-cw-flavan-3-ol methylether acetate derivatives ( 20%) (62a and 62b) in excellent enantiomeric excesses (>99%). The optical purity was assessed by H NMR using [Eu(hfc)3] as chiral shift reagent. The absolute configuration of the derivatives of the tram- and cii-flavan-3-ol derivatives was assigned by comparison of CD data with those of authentic samples in the catechin or epicatechin series flavan-3-ols. Thus, the absolute configuration of the flavan-3-ol methyl ether acetates confirms the assigned configuration of the diols as derived from the Sharpless model. 

The rare series of naturally occurring flavan-3-ols with an additional pyran ring" was extended by identification of the two epicatechin analogs 83 and 84, as well as four... 

We also need to point out the often improper use of proanthocyanidin nomenclature. In Ref. 104, both vitisinol (125) and amurensisin (126) were classified as procyanidins per definition they do not belong to this class of compounds (Figure 11.11). Vitisinol (125) is rather a member of the nonproanthocyanidin class with flavan or flavan-3-ol constituent units (see Section 11.3.3), while amurensisin (126) is simply a gallic acid derivative of epicatechin (see Section 11.3.1.2). 

Earlier proposals (12, 13, U) and the results of biosynthetic experiments (18) have been adumbrated into a scheme of biosynthesis for the procyanidins (Figure k) in which it is suggested that they are formed as byproducts during the final stage of the synthesis of the parent flavan-3-ol structures, (+)-catechin and (-)-epicatechin (11, 18). A two step reduction of the f1av-3-en-3-ol... 

The flavan-3-ols most occurring in nature are (+)-catechin and (-)-epicatechin (EC), although gallocatechin and epigallocatechin have also been identified [42]. Proanthocyanidins (or condensed tannins) include oligo- and polymeric forms of the monomeric flavanols and will be examined later. Polymerization of monomeric flavanols can occur as a result of auto-oxidation, but more often it is catalyzed by polyphenoloxidase (PPO), an enzyme that is present in most plant tissues [43]. 

Condensed tannins are also referred to as proanthocyanidins. They are oligomeric or polymeric flavonoids consisting of flavan-3-ol (catechin) units. Hydrolysis under harsh conditions, such as heating in acid, yields anthocyanidins. An example of a condensed tannin is procyanidin B2 (epicatechin-(4 3—>8 )-epicatechin 1.90). In this case the interflavanyl linkage is between C4 of the lower unit, and C8 of the upper unit. The linkage can also be between C4 of one unit and C6 of the second unit. 

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