Alkaloids 1 and 2 are the first vobasinyl−ibogan-type
alkaloids possessing a six-membered ring via an ether linkage
between C-17 and C-21. The cytotoxicities of all alkaloids
except 3 against five human cancer cell lines were evaluated
using the MTT method reported previously.26 Cononitarine B
and conophylline exhibited significant inhibitory effects against
these five human cancer cell lines, and alkaloids 1, 7,
ervachinine A, ervachinine B, ervachinine C, and conofoline
displayed moderate cytotoxicity against some of the cell lines
(Table 4).