Taburnaemines A–I, Cytotoxic Vobasinyl-Iboga-Type Bisindole Alkaloids from <i>Tabernaemontana corymbosa</i>

Nineteen vobasinyl-ibogan-type bisindole alkaloids, including nine new compounds, taburnaemines A–I (<b>1</b>–<b>9</b>), were isolated from the twigs and leaves of <i>Tabernaemontana corymbosa</i>. The structures and absolute configurations of the new alkaloids were determined by a combination of MS, NMR, and ECD analyses. Alkaloids <b>1</b>–<b>5</b> contain a rare 1,3-oxazinane moiety in the vobasinyl unit, while <b>6</b> has an uncommon 1,3-oxazolidine moiety in the iboga unit. The absolute configurations of alkaloid <b>1</b> and the known alkaloid tabernaecorymbosine A (<b>10</b>) were confirmed by single-crystal X-ray diffraction analysis. All of the bisindole alkaloids, except <b>2</b> and 16′-decarbomethoxy­tabernaecorymbosine A (<b>14</b>), 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

Taburnaemines A–I, Cytotoxic Vobasinyl-Iboga-Type Bisindole Alkaloids from <i>Tabernaemontana corymbosa</i>

Nineteen vobasinyl-ibogan-type bisindole alkaloids, including nine new compounds, taburnaemines A–I (<b>1</b>–<b>9</b>), were isolated from the twigs and leaves of <i>Tabernaemontana corymbosa</i>. The structures and absolute configurations of the new alkaloids were determined by a combination of MS, NMR, and ECD analyses. Alkaloids <b>1</b>–<b>5</b> contain a rare 1,3-oxazinane moiety in the vobasinyl unit, while <b>6</b> has an uncommon 1,3-oxazolidine moiety in the iboga unit. The absolute configurations of alkaloid <b>1</b> and the known alkaloid tabernaecorymbosine A (<b>10</b>) were confirmed by single-crystal X-ray diffraction analysis. All of the bisindole alkaloids, except <b>2</b> and 16′-decarbomethoxy­tabernaecorymbosine A (<b>14</b>), 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

Tabercorymines A and B, Two Vobasinyl–Ibogan-Type Bisindole Alkaloids from Tabernaemontana corymbosa

Tabercorymines A (<b>1</b>) and B (<b>2</b>), two new vobasinyl–ibogan-type bisindole alkaloids with an unprecedented skeleton, were isolated from Tabernaemontana corymbosa. Their structures were established by a combination of spectroscopic data, chemical transformation, single-crystal X-ray diffraction, and ECD calculation. Compound <b>1</b> represents a novel bisindole alkaloid, characterized by a caged heteropentacyclic ring system incorporating an unprecedented C-7/C-20 bond in the vobasinyl unit. Alkaloids <b>1</b> and <b>2</b> showed potent antiproliferative activity against several human cancer cell lines, including vincristine-resistant KB