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■ Hydrolysable Tannins Isolated from Syzygium aromaticum: Structure of a New C-Glucosidic Ellagitannin and Spectral Features of Tannins with a Tergalloyl Group

Li-Ming Bao, _ Eerdunbayaer, Akiko Nozaki, Eizo Takahashi, Keinosuke Okamoto, Hideyuki Ito, and Tsutomu Hatano*

*Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, 1-1-1 Tsushima-naka, Okayama 700-8530, Japan

Abstract

Eighteen hydrolysable tannins, including a new C-glucosidic tannin named aromatinin A (1), were isolated from an aqueous acetone extract of dried flower buds of Syzygium aromaticum Merr. et Perry. We determined that 1 had a gallic acid C-glucoside structure, based on the spectral data and synthesis from casuarinin (18) and gallic acid (20). This is a rare example of hydrolysable tannins with gallic acid C-glucoside structure. We also report the 1H nuclear magnetic resonance (NMR) spectral features of syzyginin A (2), bicornin (3), and platycaryanin A (4), which were also isolated from S. aromaticum, based on their structures with a tergalloyl group or its depsidone form. The remaining known compounds were identified as alunusnin A (5), rugosin C (6), 1,2,3-tri-O-galloyl-β-D-glucose (7), 1,2,3,6-tetra-O-galloyl-β-D-glucose (8), tellimagrandin II (9), casuarictin (10), heterophylliin D (11), rugosin D (12), rugosin F (13), euprostin A (14), 1,2-di-O-galloyl-3-O-digalloyl-4,6-O-(S)-hexa- hydroxydiphenoy-β-D-glucose (15), alienanin B (16), squarrosanin A (17), and 18. The antifungal effects of hydrolysable tannins, 9, 12, and 18 against Candida strains are also described.