Galloyl ester

The initial oxidation of the flavanol components of fresh leaf to quinone structures through the mediation of tea polyphenol oxidase is the essential driving force in the production of black tea. While each of the catechins is oxidizable by this route, epigallocatechin and its galloyl ester are preferentially oxidized.68 Subsequent reactions of the flavonoid substances are largely nonenzymic. 

The organoleptic properties of black tea depend to a considerable extent on the astringency resulting from the interaction of caffeine with the oxidized galloyl ester of the flavanols. The aroma components of black tea also constitute a unique flavor profile that blends well with the taste of the nonvolatile materials. The caffeine provides a moderate level of stimulation, which adds further to the appeal of the beverage, although tea has been shown to provide relaxation as well as revival of character.119... 

Building blocks Gallic acid, galloyl ester, ester-linked with glucose Flavanoid units (Procyanidins), catechin... 

However, the true novelty comes with four O-galloyl esters identified in Terminalia and Pelargonium, six O-methylbutyryl esters in Trollius one O-malonyl ester in Beta, and one 0-(3-hydroxy-3-methyl)glutaroyl ester in Glycyrrhiza. ... 

Terminalia catappa, Combretaceae, commonly used in the folk medicine in Taiwan, contains several C-glycosylflavones, two of them galloyl esters of vitexin and isovitexin. The isolated compounds were tested for antioxidative activity on Cu " /02-induced low-density lipoprotein peroxidation. IC50 values were 2.1 pM for vitexin derivatives and 4.5 pM for isovitexin derivatives compared to 4.0 pM for probucol chosen as positive control. 

Galloyl esters having antioxidant properties have been prepared, but have not reached significant application.133 135... 

Penta-O-galloyl-P- D-glucose (galloyl ester) Rhodiola sachalinensis (Polygonaceae) PEP (170 nM) [117]... 

Fig. 9D.4 Preferred conformation of dimer B2-3 - O-gallate (B2G) and suggested conformational arrangements of the oenin intercalated between the galloyl ester group and catechol ring B of B2G (adapted from Berke and de Freitas 2005)...

MW of the terminal catechin unit, c degree of polymerization, g number of galloyl ester, 23 Na atomic mass (Krueger et al., 2000). 

It is well known that tea contains catechins besides caffeine. Although catechins are widely distributed in the plant kingdom, the catechin monomers in many plants coexist with larger amounts of dimeric to polymeric proanthocyanidins, which are comprised of catechin units connected by C-C bonds. However, the polyphenol composition of C. sinensis is unique, and mainly comprised of four monomeric catechins—(-)-epicatechin (1), (-)-epigallocatechin (2) and their galloyl esters. 

In the oxidation of tea catechins, the initial reaction gave simple catechin quinones. However, subsequent cross-coupling reactions of the quinones yielded many products. Some of these products were unstable and decomposed to give further complex products. These cascade-type reactions account for the complexity of the black tea polyphenols (figure 5.9). Although many of the oxidation products described here were obtained by model fermentation experiments, the presence of compounds 21, 24,26,28, and 29, as well as theaflavins (theaflavin and its galloyl esters), theasinensins (14-17), and oolongtheanins (18), in commercial black tea were confirmed. 

Inhibition of the Chymotrypsin-like Activity of Purified Proteasomes by Galloyl-Ester-Containing Polyphenols... 

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