Abstract
Sakuraso-saponin (3), a pentaglycoside of protoprimulagenin A (1), has been isolated from the root of Primula sieboldi E. MORREN (Primulaceae, Japanese name : sakuraso). Complete acid hydrolysis of sakuraso-saponin (3) furnished primulagenin A (2), glucose, galactose, rhamnose, and glucuronic acid, while the ultraviolet irradiation of sakuraso-saponin liberated the genuine aglycone protoprimulagenin A (1) in a good yield. On the bases of the chemical and physicochemical investigations of the prosapogenols : PS-1 (4), PS-2 (5), PS-3 (6), and PS-4 (7), and a pentaglycoside PS-5 (8), in addition to those of sakuraso-saponin (3), the full structure of sakuraso-saponin has been established as 3-O-{4-O-[α-L-rhamnopyranosyl (1→2)-α-L-rhamnopyranosyl (1→2)-β-D-galactopyranosyl (1→4)]-2-O-β-D-glucopyranosyl (1→2)-β-D-glucuronopyranosyl}-protoprimulagenin A (3), which is a first structure determination of the primulaceous saponins.
