| Summary: | The aim of this study was to characterize hydrolyzable tannins in Polygonaceous plants, as only a few plants have previously been reported to contain ellagitannins. From <i>Persicaria chinensis</i>, a new hydrolyzable tannin called persicarianin was isolated and characterized to be 3-<i>O</i>-galloyl-4,6-(<i>S</i>)-dehydrohexahydroxydiphenoyl-<span style="font-variant: small-caps;">d</span>-glucose. Interestingly, acid hydrolysis of this compound afforded ellagic acid, despite the absence of a hexahydroxydiphenoyl group. From the rhizome of <i>Polygonum runcinatum</i> var. <i>sinense</i>, a large amount of granatin A, along with minor ellagitannins, helioscpoinin A, davicratinic acids B and C, and a new ellagitannin called polygonanin A, were isolated. Based on 2D nuclear magnetic resonance (NMR) spectroscopic examination, the structure of polygonanin A was determined to be 1,6-(<i>S</i>)-hexahydroxydiphenoyl-2,4-hydroxychebuloyl-β-<span style="font-variant: small-caps;">d</span>-glucopyranose. These are the second and third hydrolyzable tannins isolated from Polygonaceous plants. In addition, oligomeric proanthocyanidins of <i>Persicaria capitatum</i> and <i>P. chinensis</i> were characterized by thiol degradation. These results suggested that some Polygonaceous plants are the source of hydrolyzable tannins not only proanthocyanidins.
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