Cytotoxic eburnamine-aspidospermine type bisindole alkaloids from Bousigonia mekongensis.

Four new eburnamine-aspidospermine type bisindole alkaloids, namely, mekongenines C-F (1-4), along with 27 known indole alkaloids were isolated from the twigs and leaves of Bousigonia mekongensis. Their structures with the absolute configurations were elucidated by spectroscopic methods and ECD analyses. All new compounds were evaluated for their cytotoxicities against five human cancer cell lines: HL-60, SMMC-7721, A-549, MCF-7 and SW480 in vitro. Alkaloids 1-4 exhibited inhibitory effects with IC50 values comparable to those of cisplatin.