THE STRUCTURE OF RUBICUNOSIDE A

A new acetylated triterpenoid saponin, rubicunoside A (1), was isolated 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)]-beta-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-fucopyranoside (1). During the enzymic cleavage with glycyrrhizinic acid hydrolase, we unexpectedly found two new characteristics of the hydrolase. It can selectively hydrolyzed not only 28-O-monoprosapogenins, but also the acetyl group in the sugar moieties of the prosapogenins. The enzymic cleavage method with glycyrrhizinic acid hydrolase providing selectivly 3-oligosaccharides and 28-O-glucosides and partial methanolysis providing selectively 28-oligosaccharides from 3,28-O-bisglucosides were effective for the structure elucidation.