New Noroleanane-Type Triterpene Saponins with Gastroprotective Effect and Platelet Aggregation Activity from the Flowers of Camellia japonica: Revised Structures of Camellenodiol and Camelledionol

The methanolic extract from the flowers of Camellia japonica was found to exhibit potent gastroprotective effect on ethanol-induced gastric mucosal lesions in rats and platelet aggregation activity.Through bioassay-guided separation, three new 28-noroleanane-type triterpene saponins, camelliosides A, B, and C, and an oleanane-type triterpene saponin, camellioside D, were isolated from the methanolic extract.The absolute stereostructures of camelliosides A-D were determined on the basis of physicochemical and chemical evidence, which included the structure revision of the triterpene part, camellenodiol and camelledionol, using X-Ray crystallographic analysis and modified Mosher's method.Camelliosides A and Bshowed gastroprotective and platelet aggregating effects.The flowers of Camellia japonica L. (Theaceae, Japanese name ''Tsubaki'') have been used for treatment of blood vomiting and bleeding due to internal and external injury, and also as an antiinflammatory, tonic, and stomatic in Japanese folk medicine and Chinese traditional medicine.As chemical constituents of this natural medicine, noroleanane-type triterpene, camellenodiol, comelledionol, and maragenin II, were reported, 1 but the constituents responsible for the traditional medicinal uses have not been identified.During the course of our chemical and pharmacological studies on the bioactive saponins and glycosides, 2 we have already reported the isolation and structure elucidation of acylated polyhydroxytriterpene oligoglycosides, camelliasaponins A 1 , A 2 , B 1 , B 2 , C 1 , and C 2 , from the seeds of C. japonica and these saponins were found to inhibit alcohol absorption in rats. 3 As a continuing study, we found that the MeOH extract from the flowers of C. japonica showed potent gastroprotective effect on ethanol-induced gastric mucosal lesions in rats and platelet aggregation activity.Through bioassayguided separation, we isolated three new 28-noroleanane-type triterpene saponins, camelliosides A (1, 0.10%, from the natural medicine), B (2, 0.067%), and C (6, 0.0052%), and an oleanane-type triterpene saponin, camellioside D (8, 0.0023%), together with oleanolic acid (0.0006%), 4 benzyl β-D-glucopyranoside (0.0004%), 5 methyl gallate (0.0003%), 4 (+)-catechin (0.0011%), 4 and (-)-epicatechin (0.038%). 4 This communication deals with the structure elucidation of 1, 2, 6 and 8, which included the structure reinvestigation of the triterpene part, camellenodiol (3) and camelledionol (4).In addition, we describe the effects of principal saponins on gastric lesions induced by ethanol in rats and the effects on rabbit platelet aggregation.Camellioside A (1), 6 colorless fine crystals from aqueous MeOH, mp 226-229°C, [α] D 26 -32.1° (c=1.8,pyridine), C 53 H 84 O 24 , showed absorption bands ascribable to hydroxyl, carbonyl, olefin, and ether functions [IR (KBr): 3453, 2962, 1736, 1719, 1656, 1078 cm -1 ].Acid hydrolysis of 1 liberated D-glucuronic acid, D-galactose, and D-glucose, which wereidentified by GLC analysis of their trimethylsilyl thiazolidine derivatives. 7Treatment of 1 with glycyrrhizinic acid hydrolase in 1.0 M acetate buffer (pH 4.4, 44°C) gave camellenodiol (3), 1 which was transformed to the 3-O-acetate (3a) and camelledionol (4) 1 by acetylation and oxidation, respectively.Since there has been considerable doubt as to the position of the