Vobasine, vincamine, voaphylline, tacaman, and iboga alkaloids from Tabernaemontana corymbosa

Thirteen indole alkaloids comprising six vobasine/sarpagine, one vincamine, two voaphylline, two tacaman, one iboga, and one corynantheine alkaloid, were isolated from the leaf extract of Tabernaemontana corymbosa (sample from Taiping, Perak, Malaysia). The structures of these alkaloids were determined based on analysis of the spectroscopic data (NMR and MS), and in the case of vincarudine, the absolute configuration was established by ECD and X-ray diffraction analysis. Vobasidine E represents the first vobasine-type alkaloid characterized by a contracted ring C and loss of the ethylidene/ethyl side chain. A possible biogenetic pathway from a perivine precursor, which was also present in the leaf extract, is presented. Differences in the new alkaloid content between the present and previous sample of the same plant (occurring in a different location) are discussed.