Constituents of Geranium thunbergii SIEB. et ZUCC. II. Ellagitannins. (1)

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Abstract
The tannin of G. thunbergii was extracted with acetone/H2O at room temperature, and the solution was extracted with EtOAc. This extract was fractionated using droplet countercurrent chromatography to yield tannin 1 and tannin 2. The relative astringency measurement and quantitative determination of ellagitannin by UV absorption of the solutions colored with NaNO2-AcOH showed that the tannin activity of this plant is mainly due to the substances in the EtOAc extract in which tannin 1 and tannin 2 are the main constituents, and that ellagitannins are the main tannin constituents. When treated with boiling water, tannin 1 was fairly rapidly hydrolyzed, and the resulting solution gave, upon fractionation after methylation, corilagin, hexahydroxydiphenoic acid, and gallic acid as their methylated derivatives. Glucose was also detected. An additional hydrolysis product, in which another galloyl group was presumed to be linked to corilagin, was obtained by treatment with boiling water for a short period. Tannin 1, therefore, would be one of the main original substances which yielded previously reported corilagin and other compounds related to tannin, which were obtained from the hot water extract.

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