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Taburnaemines A-I, Cytotoxic Vobasinyl-Iboga-Type Bisindole Alkaloids from Tabernaemontana corymbosa
Yu Zhang1, Yu-Xi Yuan1, Masuo Goto2
1State Key Laboratory of Phytochemistry and Plant Resources in West China , Kunming Institute of Botany, Chinese Academy of Sciences , Kunming 650201 , Yunnan , People's Republic of China.
Abstract:
Nineteen vobasinyl-ibogan-type bisindole alkaloids, including nine new compounds, taburnaemines A-I (1-9), were isolated from the twigs and leaves of Tabernaemontana corymbosa. The structures and absolute configurations of the new alkaloids were determined by a combination of MS, NMR, and ECD analyses. Alkaloids 1-5 contain a rare 1,3-oxazinane moiety in the vobasinyl unit, while 6 has an uncommon 1,3-oxazolidine moiety in the iboga unit. The absolute configurations of alkaloid 1 and the known alkaloid tabernaecorymbosine A (10) were confirmed by single-crystal X-ray diffraction analysis. All of the bisindole alkaloids, except 2 and 16'-decarbomethoxytabernaecorymbosine A (14), showed antiproliferative activity (IC50 2.6-9.8 μM) against several human cancer cell lines, including A-549, MDA-MB-231, MCF-7, KB, and P-glycoprotein-overexpressing multidrug-resistant KB cells. The preliminary structure-activity relationship correlations are also discussed.
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