TANNINS AND RELATED-COMPOUNDS .124. 5 NEW ELLAGITANNINS, PLATYCARYANIN-A, PLATYCARYANIN-B, PLATYCARYANIN-C, AND PLATYCARYANIN-D, AND PLATYCARIIN, AND A NEW COMPLEX TANNIN, STROBILANIN, FROM THE FRUITS AND BARKOF PLATYCARYA-STROBILACEA SIEB ET ZUCC, AND BIOMIMETIC SYNTHESIS OF C-GLYCOSIDIC ELLAGITANNINS FROM GLUCOPYRANOSE-BASED ELLAGITANNINS

Five new ellagitannins, platycaryanins A (27), B (26), C (30), and D ( 25), and platycariin (31), and a new complex tannin, strobilanin (32), have been isolated from the fruits and bark of Platycarya strobilacea SIEB. et ZUCC. (Juglandaceae), together with twenty-six known compoun ds. On the basis of spectroscopic and chemical evidence, platycaryanin s A, B and C, and platycariin have been characterized as the ellagitan nins having a tergalloyl ester group, while platycaryanin D was found to be an unusual ellagitannin possessing (R)-hexahydroxydiphenoyl este rs at the glucopyranose 2,3- and 4,6-positions. During these chemical studies, re-examination of the similar ellagitannins, alnusnins A and B, which were previously reported from Alnus sieboldiana, led us to re vise their structures to 29 and 28, respectively, in which the tergall oyl group forms a lactone ring. Furthermore, biomimetic conversion of ellagitannins having a glucopyranose core into C-glycosidic ellagitann ins was successfully achieved for the first time, and the reaction was applied to the structure elucidation of platycariin (31).