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

Tabercorymines A
(1) and B (2), 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 1 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 1 and 2 showed potent antiproliferative activity
against several human cancer cell lines, including vincristine-resistant
KB.