Biscarpamontamines A and B, an Aspidosperma−Iboga Bisindole Alkaloid and an Aspidosperma−Aspidosperma Bisindole Alkaloid, from <i>Tabernaemontana sphaerocarpa</i>

Two new bisindole alkaloids, biscarpamontamine A (1), possessing an aspidosperma−iboga-type skeleton, and biscarpamontamine B (2), having an aspidosperma−aspidosperma-type skeleton, were isolated from stems of Tabernaemontana sphaerocarpa, and their structures were elucidated on the basis of spectroscopic data analysis. The absolute configuration of biscarpamontamine B (2) was established by comparison of its CD spectrum and with that of vobtusine (3). Biscarpamontamine B (2) showed potent cytotoxicity against various human cancer cell lines.