Tannins and related compounds. XCVII. Structure revision of C-glycosidic ellagitannins, castalagin, vescalagin, casuarinin and stachyurin, and related hydrolyzable tannins.

Abstract

The structures of the C-glycosidic ellagitannins, castalagin, vescalagin, casuarinin and stachyurin, have been revised to 1-4 respectively, on the basis of two-dimensional nuclear Overhauser effect (NOE) spectroscopy and NOE difference spectroscopy. Furthermore, the structures of some related C-glycosidic tannins were re-examined by using similar techniques, and it was concluded that the configuration at the glucose C-1 position in all hitherto known C-glycosidic tannins must be revised.