Molluscicidal saponins from Catunaregam nilotica.

Two new saponins were isolated from the fruits of Catunaregam nilotica Stapf, syn. Lachnosiphonium nilotica; Randia nilotica; Xeromphis nilotica. Their structures were determined mainly by spectroscopic methods as 3- O-[O-alpha-L-rhamnopyranosyl-(1-->3)-O-[O-beta-D-glucopyranosyl-(1 -->3)]- beta-D-glucopyranosyl]oleanolic acid and 28-O-beta-D- glucopyranosyl-3-O-[O-alpha-L-rhamnopyranosyl-(1-->3)-O[O-beta-D- glucopyranosyl]-beta-D-glycopyranosyl]oleanolate. The monodesmosidic saponin is a potent molluscicide against the schistosomiasis transmitting snail Biomphalaria glabrata with a LC50 value of 3 ppm. In addition two known saponins, 3-O-[2', 3'-di-O-(beta-D-glucopyranosyl)-beta-D- glucopyranosyl]oleanolic acid and 3-O-[O-beta-D-glucopyranosyl(1-->3)- beta-D-glucopyranosyl]oleanolic acid, were identified and their molluscicidal activity determined, the LC50 values being 26 and 3 ppm, respectively. Initial molluscicidal screening of the crude water and ethanol extracts revealed 100% snail mortality at concentrations of 100 and 50 ppm, respectively. The haemolytic activity of the molluscicidal saponins was determined as well and the HC50 values towards bovine erythrocytes found to be 3 ppm for the new saponin, and 16 and 2 ppm, respectively, for the two known saponins.