Bioactive Saponins and Glycosides. XXIII. Triterpene Saponins with Gastroprotective Effect from the Seeds of Camellia sinensis—Theasaponins E₃, E₄, E₅, E₆, and E₇—

抄録

The saponin fraction from the seeds of the tea plant [Camellia sinensis (L.) O. KUNTZE (Theaceae)] was found to exhibit potent protective effects on ethanol- and indomethacin-induced gastric mucosal lesions in rats. Five new triterpene saponins, theasaponins E₃ (1), E₄ (2), E₅ (3), E₆ (4), and E₇ (5), were isolated together with 11 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 E₁ (6), E₂ (7), and E₅ (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 omeplazole. 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.