New Cytotoxic Indole Alkaloids from <i>Tabernaemontana </i><i>c</i><i>alcarea </i>from the Madagascar Rainforest

Bioassay-directed fractionation of the alkaloid portion of a CH₂Cl₂−MeOH extract of Tabernaemontana calcarea resulted in the isolation of the three new cytotoxic indole alkaloids, 1−3, and the 12 known alkaloids voacangine (4), isovoacangine (5), coronaridine (6), 11-hydroxycoronaridine (7), voacristine (8), 19-epi-voacristine (9), isovoacristine (10), ibogamine (11), 10-methoxyibogamine (12), 11-methoxyibogamine (13), heyneanine (14), and 19-epi-heyneanine (15). The structures of the new compounds 1−3 were elucidated on the basis of extensive 1D and 2D NMR spectroscopic interpretation. All the compounds exhibited cytotoxic activity against the A2780 ovarian cancer cell line.