RESUMO
Roasting of green tea causes oligomerization of tea catechins, which decreases the astringency. The aim of this study was to elucidate the oligomerization mechanism. The 13C NMR spectrum of the oligomer fraction showed signals arising from catechin and sugar residues. Heating of epigallocatechin-3-O-gallate with 13C-labeled glucose (150⯰C for 2â¯h) suggested that condensation of sugars with catechin A-rings caused the oligomerization. The dimeric product obtained by heating for a shorter period (30â¯min) suggested cross-linking occurred between sugars and catechin A-rings. Furthermore, heating of phloroglucinol, a catechin A-ring mimic, with glucose, methylglyoxal, and dihydroxyacetone, confirmed that the basic mechanism included reaction of the catechin A-ring methine carbons with carbonyl carbons of glucose and their pyrolysis products.
Assuntos
Catequina/química , Chá/química , Isótopos de Carbono/química , Catequina/análogos & derivados , Cromatografia Líquida de Alta Pressão , Marcação por Isótopo , Espectroscopia de Ressonância Magnética , Folhas de Planta/química , Folhas de Planta/metabolismo , Polimerização , Espectrofotometria , Açúcares/química , Chá/metabolismo , TemperaturaRESUMO
Theacitrins A-C are yellow pigments of black tea that are produced by oxidative coupling of gallocatechins, i.e., flavan-3-ols with pyrogallol-type B-rings. However, their stereostructures have not yet been determined. In this study, DFT calculations of NMR chemical shifts of theacitrin C (1) and TDDFT calculations of the ECD spectra of theacitrinin A (5), a degradation product of theacitrin C (1), were used to determine the stereostructure of the theacitrins. Furthermore, the preparation of theacitrins A (4) and C (1) by enzymatic oxidation of an epigallocatechin (7) and epigallocatechin-3-O-gallate (2) mixture confirmed their structural relationship.
Assuntos
Catequina/análogos & derivados , Catequina/química , Pigmentos Biológicos/química , Chá/química , Camellia sinensis , Catequina/farmacologia , Estrutura Molecular , Ressonância Magnética Nuclear Biomolecular , Oxirredução , PolifenóisRESUMO
The wood of Platycarya strobilacea Sieb. et Zucc. (Juglandaceae) was used as incense. In this study, three new sesquiterpenes (2, 4, 5) and one nor- sesquiterpene (3) were isolated and their structures determined as 7-hydroperoxy-11-hydroxy-2,4-cycloeudesman-8-one (2), 8-hydroxy-13-nor-2,4- cycloeudesman-7-en-I 1-one (3), 2,4-cycloeudesma-7(11), 8-dien-(12,8)-olide (4), and 8-hydroxy-8,12-peroxy-2,4-cycloeudesm-7(l I)-ene (5). In addition, the absolute configuration of a previously reported sesquiterpene was revised based on the calculation of its ECD spectrum.
