Structure of isorugosin b, and the orientation of valoneoyl group in the related monomeric, dimeric and trimeric hydrolyzable tannins

A new hydrolyzable tannin, named isorugosin B (1), was isolated from Liquidambar formosana, and the structure in which the orientation of valoneoyl group at 0-4 ~ 0-6 of the glucose core is the reverse of that in rugosin B (2) and in rugosin A (3), was determined. The orientation of valoneoyl group in rugosin A (3) was established by the long range ¹H¹³C correlation nmr spectroscopy. The structures of rugosins D (6), E (7) and G (8), coriariins C (9), D (10), E (11) and F (12), cornusiin A (13), camptothins A (b15) and B (16), were fully established on the basis of chemical correlations with 1 or 3.