Structures of three new oleanene glucuronides isolated from Lathyrus palustris var. pilosus and hepatoprotective activity.

Three new saponins, named palustrosides I, II and III, together with azukisaponins II, V and soyasapogenol B monoglucuronide, were isolated from the aerial parts of Lathylus palustris L. var. pilosus Ledeb. The structures of palustrosides I, II and III were identified as 3-O-beta-D-glucopyranosyl-(1-->2)-beta-D-glucuronopyranosides of soyasapogenol E, abrisapogenol E, and bredemolic acid 28-O-beta-D-glucopyranoside, respectively, by spectroscopic and chemical methods. As part of our studies on hepatoprotective drugs, we also examined the hepatoprotective effects of these saponins towards immunologically induced liver injury in primary cultured rat hepatocytes. The activity of the disaccharide group was greater than that of the trisaccharide group. This information regarding the structure-activity relationships substantiated previously obtained data. Structure-hepatoprotective relationships for the sapogenol moiety suggested that the hydroxyl group at C-30 reduces the hepatoprotective effect. On the other hand, the carbonyl group at C-22 may be equivalent to a hydroxyl group at C-22 in terms of hepatoprotective action. Oleanolic acid-type saponins also exhibited hepatoprotective action.