Two Novel Sarpagine-Type Indole Alkaloids from the Leaves of Hunteria zeylanica in Thailand

Investigation of the leaves and stems of Hunteria zeylanica resulted in the isolation of one new indole alkaloid, 11-hydroxyrhazimanine (1), and nine known analogs 2-10. Their structures were determined by 1D and 2D NMR analyses. Decarbomethoxydihydrogambirtannin (2), dihydroantirhine (3), and 3-oxomehranine (4) were isolated from Hunteria genus for the first time.The genus Hunteria (Apocynaceae), which includes eight species, is distributed mainly in the tropical areas of Asia and Africa. Hunteria zeylanica (Retz.) is the only species endemic in Hainan Province, China. This plant has been used by the natives as medicine to cure yaws and reduce boils and skin irritations [1].Previous chemical investigations on the Hunteria genus have led to the isolation of more than 45 indole alkaloids [2][3][4][5][6][7][8]. Nearly 30 of them were reported from H. zeylanica. In this paper, we describe the isolation and chemical characterization of 10 indole alkaloids from H. zeylanica, including one new compound, named 11-hydroxyrhazimanine (1), and nine known ones, i.e., decarbomethoxydihydrogambirtannin (2) [9], dihydroantirhine (3) [10], 3-oxomehranine (4) [11], eburnamonine (5) [12], eburnamenine (6) [12], eburnamine (7) [12], pleiocarpamine (8) [13], geissoschizol (9) [14], and tuboxenine (10) [15].

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