Bioactive saponins and glycosides.: XXIII.: Triterpene saponins with gastroprotective effect from the seeds of Camellia sinensis -: Theasaponins E3, E4, E5, E6, and E7

The saponin fraction from the seeds of the tea plant vertical bar Camellia sinensis (L.) O. Kuntze (Theaceae)vertical bar was found to exhibit potent protective effects on ethanol- and indomethacin-induced gastric mucosal lesions in rats. Five new triterpene saponins, theasaponins E-3 (1), E-4, (2), E-5 (3), E-6 (4), and E-7 (5), were isolated together with I I known saponins from the saponin fraction. The chemical structures of 1-5 were elucidated on the basis of chemical and physicochemical evidence. Among the isolated saponins, theasaponins E-1 (6), E-2 (7), and E-5 (3) and assamsaponin C (10) showed an inhibitory effect on ethanol-induced gastric mucosal lesions at a dose of 5.0 mg/kg, p.o. and their activities were stronger than that of onieplazole. With regard to the structure-activity relationships of theasaponins, the following structural requirements for a protective effect on ethanol-induced gastric lesions were suggested; 1) the 21- and/or 22-acyl groups are essential for the activity, 2) acetylation of the 16-hydroxyl group reduce the activity.