THE STRUCTURE OF RUBICUNOSIDE A

A new acetylated triterpenoid saponin, rubicunoside A (1), was isolate d from the roots of Silene, rubicunda Franch. It was characterized on the basis of extensive chemical, enzymic, and spectral methods as 3-O- beta-D-galactopyranosyl-(1 --> 2)-[beta-D-xylopyranosyl-(1 --> 3)]-bet a-D-glucuronopyranosyl quillaic acid 28-O-beta-D-xylopyranosyl-(1 --> 3)-beta-D-xylopyranosyl-(1 --> 4)-alpha-L-rhamnopyranosyl-(1 --> 4)-[2 ''-OAc-beta-D-quinovopyranosyl-(1 --> 2)]-[3'-OAc]-beta-D-fucopyranosi de (1). During the enzymic cleavage with glycyrrhizinic acid hydrolase , we unexpectedly found two new characteristics of the hydrolase. It c an selectively hydrolyzed not only 28-O-monoprosapogenins, but also th e acetyl group in the sugar moieties of the prosapogenins. The enzymic cleavage method with glycyrrhizinic acid hydrolase providing selectiv ly 3-oligosaccharides and 28-O-glucosides and partial methanolysis pro viding selectively 28-oligosaccharides from 3,28-O-bisglucosides were effective for the structure elucidation.