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■ Dimeric Flavans from Gambir and Their Structural Correlations with (+)-Catechin

Shoko Taniguchi, Kayo Kuroda, Kou-ichi Doi, Masahiro Tanabe, Takashi Shibata, Takashi Yoshida, and Tsutomu Hatano*

*Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Tsushima, Okayama 700-8530, Japan

Abstract

We isolated two new flavan dimers, gambirflavan D3 (10) and gambirflavan D4 (12), together with gambiriin A3 (11), from gambir, a hot-water extract of the leaves and young twigs of Uncaria gambir. Because their spectral analyses suggested that they are derived from catechin, we conducted a conversion reaction using (+)-catechin (1) to produce these dimers; another new flavan, gambirflavan D5 (13), was obtained as a product of this reaction. The structural relationship of these dimeric flavans with (+)-catechin (1) is discussed.