A-Catechin

Fig. Electropherogram of a) catechin standards, b) green tea sample prepared in 50 % methanol using liquid extraction...

WANG E, BARECKi-ROACH M, JOHNSON w (2002) Elevation of P-glycoprotein function by a catechin in green tea. Biochem Biophys Res Commun. 297 412. 

Superoxide anion scavenging activity of the enzymatically synthesized poly(catechin) was evaluated. Poly(catechin), synthesized by HRP catalyst, greatly scavenged superoxide anion in a concentration-dependent manner, and almost completely scavenged at 200 p.M of a catechin unit concentration. The laccase-catalyzed synthesized poly(catechin) also showed excellent antioxidant property. Catechin showed pro-oxidant property in concentrations lower than 300 jlM. These results demonstrated that the enzymatically synthesized poly(catechin) possessed much higher potential for superoxide anion scavenging, compared with intact catechin. 

Fig. 3.1 Structures of (a) catechin, (b) epicatechin, (c) epicatechin gallate, (d) general structure of PAs, and (e) procyanidin dimer...

The electrophilic primary and secondary quinones undergo addition of nucleophiles, including flavonoids. For instance, nucleophilic addition of catechin to its enzymatically generated quinone yielded a catechin dimer in which the catechin moieties are linked through a C6 C8 biphenyl linkage. This B-type dehydrodicatechin further oxidized to yellow pigments. Additional dehydrodicatechins arise from radical coupling of the catechin semi-quinones formed by retro-disproportionation, in which the catechin moieties are linked... 

Based on these principles, Jurd (29) described the most likely reactions (Figure 2). One leucocyanidin molecule 25 reacts with a flavan molecule 26a or 26b yielding dimers 27a, 27b, 28a, or 28b. If the second flavan molecule is also a leucocyanidin (R = OH), the dimer again contains a benzylic alcohol (OH) and the condensation can continue. If this second molecule is a catechin (R = H), condensation cannot go beyond the dimer, which is a proanthocyanin. Proanthocyanins in plant tissues have long been known (30). 

Identify proanthocyanidin subunits by comparing their retention factors to those shown in Table 11.4.1. After identification, quantify using a (+)-catechin standard. 

Subunits that react with phloroglucinol are derived from proanthocyanidin extension subunits. Subunits that have not reacted with phloroglucinol are derived from proanthocyanidin terminal subunits or were present as monomeric flavan-3-ols. For quantitation, the sample peak areas of the individual subunits are compared with a(+)-catechin standard, and individual quantities are determined using the relative response factors shown in Table 11.4.1. 

Complex tannins are defined as tannins in which a catechin unit (1.39) is bound glycosidically to either a gallotannin or an ellagitannin unit. As the name implies, the structure of these compounds can be very complex. An example is Acutissimin A (1.99). This is a flavogallonyl unit bound glucosidically to Cl, with an additional three hydrolyzable ester bonds to a D-glucose-derived open-chain polyol. 

C.I. Natural Brown 3, 75250 (catechu) has the basic structure of catechin (2) and is a condensed tannin, e.g., gambier from leaves and twigs of the Uncaria gambler bush. Many of these tanning agents are based on a catechin flavanoid. 

Fig. 9D.9 Absorption spectra in the visible region of a catechin-Mv3glc direct condensation dimer as a function of pH (adapted from Salas et al. 2004b with permission from Elsevier)...

Figure 20-10. UV chromatogram of the on-flow experiment injecting a mixture of eight flavonoids (A catechin -i- epicatechin B flsetin C quercetin D apigeniu E narin-genin F baicalein G galangin). (Reprinted from reference 40, copyright 2003, with permission from Elsevier.)...

The first one is the classical acetaldehyde-induced tannin-anthocyanin addition described in the literature. Detection of a catechin-ethanol adduct by LC-... 

Fig. 4 MS data on the on-flow experiment of the eight flavonoids (A Catechin + Epicatechin B Fisetin C Quercetin D Apigenin E Naringenin F Baicalein G Galangin).

A Catechin + Epichatechin B Fisetin C Quercetin D Apigenin E Naringenin F Baicalein G Galangin). 

Y.B. (2008) Direct electrochemistry of laccase immobilized on au nanoparticles encapsulated-dendrimer bonded conducting polymer application for a catechin sensor. Analytical Chemistry, 80 (21), 8020-8027. 

The oxidised polyphenols give the black colour, its aroma depends on the occurrence of a volatile oil and the tannins of a catechin type give the harsh taste. The caffeine content of a cup of tea is approximately 30—40 mg. 

The crucial question for the final chromatographic analysis is, which procyanidins are to be expected in a given matrix. Naturally occurring procyanidins predominantly consist of either (-)-epicatechin or (+)-catechin. In the (-)-epicatechin series procyanidins B2, B5, Cl and an (-)-epicatechin tetramer co-occur (i.e. in Crataegus sp.), while principal components in the (-t-)-catechin series are procyanidins B3, B6, C2 and a (+)-catechin tetramer (i.e. in Salix sp.). Predominance of procyanidins B1 (i.e. in Rubus sp.) or B4 (i.e. in Sorghum sp.) is relatively seldom in the plant kingdom. The main procyanidins are always accompanied by the... 

The color of white wines therefore involves the oxidation of phenolic compounds. However, the consequences of enzymatic and chemical oxidation are not the same. Chemical oxidation of a catechin solution produces maximum absorption at 400 nm, with a more intensely yellow color than in solutions where oxidation is catalyzed by laccase. 

The prodelphinidins are less well characterized. Barley and beer contain a biflavan which gives catechin and delphinidin (58) on treatment with acid in agreement with structure (53) with either procyanidin B-1 or B-3 stereochemistry [51, 54]. Evidence for the occurrence of a [catechin-gallocatechin]... 

From diseased shoot cortical tissues of the paper mulberry, six 1,3-diphenylpropane derivatives, a catechin, a flavan, two chalcones, and a coumarin, were isolated as phytoalexins. They were brousson-... 

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