New vobasinyl-ibogan type bisindole alkaloids from Tabernaemontana corymbosa

Ten vobasinyl-ibogan type bisindole alkaloids, including three new ones, tabercorines A–C (1–3), and a new natural product, 17-acetyl-tabernaecorymbosine A (4), were isolated from the twigs and leaves of Tabernaemontana corymbosa. Their structures were elucidated on the basis of spectroscopic data, and the NMR data of 17-acetyl-tabernaecorymbosine A (4) was assigned and reported for the first time. The absolute configurations of 1–4 were determined by CD exciton chirality method. All new compounds were evaluated for in vitro cytotoxicity against various human cancer cell lines. Compounds 1 and 4 showed significant inhibitory effects with IC50 values comparable to those of cisplatin.

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