STUDIES ON THE CONSTITUENTS OF THLADIANTHA-DUBIA BUNGE .2. STRUCTURES OF DUBIOSIDE-D, DUBIOSIDE-E AND DUBIOSIDE-F, NEUTRAL SAPONINS OF QUILLAIC ACID ISOLATED FROM THE TUBER

Three neutral 3,28-0-bisdesmosidic glycosides of quillaic acid, named dubiosides D, E and F, were isolated from the tuber of Thladiantha dubia bunge (Cucurbitaceae). Their structures were elucidated on the basis of chemical and spectral evidence. All dubiosides have a common prosapogenin structure, 3-0-[0-β-D-glucopyranosyl-(l->3)-[0-/f-D-galacto-pyranosyl-(l->2)]-/J-D-glucopyranosyl]-quillaic acid, and differ only in the structures of the ester-linked sugar moieties. Dubioside D is a 28-[0-a-L-rhamnopyranosyl-(l->2)-a-L-arabinopyranosyl] ester, dubioside E, a 28-[0-/f-D-xylo'-pyranosyl-(l-+4)-0-a-L-rhamnopyranosyI-(l->2)-a-L-arabinopyranosyl] ester and dubioside F, a 28-[0-/f-D-xylopyranosyl-(l -3)-0-β-D-xylopyranosyl-(l-4)-0-a-L-rhamnopyranosyl-(l-2)-a-L-arabinopyranosyl] ester of the prosapogenin. © 1990, The Pharmaceutical Society of Japan. All rights reserved.