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-β-D-galactopyranosyl-(1→2)-[β-D-xylopyranosyl-(1→3)]-β -D-glucuronopyranosyl quillaic acid 28-O-β-D-xylopyranosyl-(1→3)-β -D-xylopyranosyl-(1→4)-α-L-rhamnopyranosyl-(1→4)-[2''-OAc-β -D-quinovopyranosyl-(1→2)]-[3'-OAc]-β-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-O0glucosides and partial methanolysis providing selectively 28-oligosaccharides from 3,28-O-bisglucosides were effective for the structure elucidation.

Key words: INFRARED SPECTROPHOTOMETRY, CARYOPHYLLACEAE