Triterpene saponins and iridoid glucosides from galium rivale.

Three new glycosides of the oleanene-type triterpenes, rivalosides C-E (1-3), along with three known triterpene saponins, momordin IIb (4) and rivalosides A-B (5-6), and five known iridoid glucosides: monotropein, scandoside, deacetylasperulosidic acid, geniposidic acid and asperulosidic acid, were isolated from aerial parts of Galium rivale. The structures of the new compounds were elucidated by spectral methods and chemical means as 2alpha-acetoxy-3alpha, 19alpha-dihydroxy-olean-12-en-28-oic acid 28-O-beta-D-glucopyranosyl-(1--> 6)-beta-D-glucopyranoside, 2alpha,3alpha, 19alpha-trihydroxy-olean- 12-en-28-oic acid 28-O-beta-D-glucopyranosyl-(1 --> 6)-beta-D-glucopyranoside and 3-O-beta-D-glucuronopyranosyl-24-hydroxy-olean-12-en-28-oic acid 28-O-beta-D-glucopyranoside, for rivalosides C-E, respectively. The taxonomic significance of the rivalosides in G. rivale was discussed.

Rivalosides A and B, two 19-Oxo triterpenoid saponins from Galium rivale.

Two new oleanene-type triterpene glycosides, rivaloside A (2alpha-acetoxy-3alpha-hydroxy-19-oxo-olean-12-en-28-o ic acid 28-O-beta-glucopyranosyl-(1-->6)-beta-D-glucopyranoside) (1) and rivaloside B (2alpha,3alpha-dihydroxy-19-oxo-olean-12-en-28-oic acid 28-O-beta-glucopyranosyl-(1-->6)-beta-D-glucopyranoside) (2), were isolated from aerial parts of Galium rivale. The structures were determined on the basis of spectroscopic data and chemical transformations. Under alkaline or acid hydrolysis, rivalosides A and B undergo allylic rearrangement with migration of the double bond. These compounds are the first representatives of 19-oxo substituted oleanenes, and they seem to be promising as taxonomic markers for G. rivale.