Chem. Pharm. Bull. 55(4) 598—605 (2007)

active saponin constituents from Camellia (C.) sinensis (Theaceae), we have reported the isolation and structure elucidation of theasaponins A1—A5, C1, E1—E13, F1—F3, G1, G2, and H1, 2—6) assamsaponins A—I, and camelliasaponins B1 and C1 9) from the seeds of Japanese C. sinensis (L.) O. KUNTZE and Sri Lankan C. sinensis L. var. assamica PERRE, and foliatheasaponins I—V from the leaves of Japanese C. sinensis. Among the saponin constituents, theasaponin E1 showed antisweet activity, 2) while theasaponins A2, E1, E2, and E5 and assamsaponins A, C, and D were found to exhibit potent inhibitory effects on gastric lesions in rats. In addition, floratheasaponins A—C (1—3) were isolated from the flower buds of Japanese C. sinensis and these acylated polyhydroxyoleanane-type triterpene oligoglycosides showed inhibitory effects on serum triglyceride elevation in olive oil-treated mice. As a continuation of our studies on bioactive constituents of medicinal flowers, the methanolic extract of the flower buds of Chinese C. sinensis was found to inhibit an immediate allergic reaction by monitoring the release of b-hexosaminidase from rat basophilic leukemia (RBL-2H3) cells. From the methanolic extract, we have isolated six new acylated oleanane-type triterpene oligoglycosides, floratheasaponins D (4), E (5), F (6), G (7), H (8), and I (9), together with 21 known compounds including floratheasaponins A—C (1—3). Furthermore, we examined the inhibitory effects of principal floratheasaponins (1—6) on the release of b-hexosaminidase from RBL-2H3 cells. In this paper, we describe the isolation and structure elucidation of the new constituents (4—9) and the inhibitory effect of major floratheasaponins (1—6) from the flower buds of Chinese C. sinensis on the release of b-hexosaminidase from RBL-2H3 cells. The methanolic extract (38.5% from the dried flower buds of C. sinensis cultivated in Anhui province of China) with the inhibitory effect on the release of b-hexosaminidase from 598 Vol. 55, No. 4