Bousmekines A-E, New Alkaloids from Two Bousigonia Species: B.angustifolia and B. mekongensis.

Four new monoterpenoid indole alkaloids, bousmekines A-D (1-4), and one new pyranopyridine alkaloid, bousmekine E (5), were isolated from the twigs and leaves of Bousigonia angustifolia and Bousigonia mekongensis. Their structures including absolute configurations were elucidated by a combination of MS, NMR, ECD calculation, and single-crystal X-ray diffraction analysis. Compound 2 was an eburnea-type MIAs characterized by a rare chlorine atom while 5 possessed a novel pyranopyridine moiety. Their cytotoxicities against several human cancer cell lines were evaluated and compound 1 exhibited significant cytotoxicity with IC50 values of 0.8-7.4 μM.