Three New Cytotoxic Monoterpenoid Bisindole Alkaloids from Tabernaemontana bufalina

Three new bisindole alkaloids, 3'-(2-oxopropyl)-19,20-dihydrotabernamine (1), 3'-(2-oxopropyl)-ervahanine B (2), 19,20-dihydrovobparicine (3), and 20 known compounds were isolated from the aerial parts of Tabernaemontana bufalina. The structures of these alkaloids were elucidated using spectroscopic methods. The absolute configurations of 1-3 were determined by the circular dichroic exciton chirality method. Compounds 1-23 were screened for their cytotoxicity against two human cancer cell lines, A-549 and MCF-7. Ten compounds (1-3, 10, 14, 16, 17, 19, 22, and 23) exhibited inhibitory effects against the two human cancer cells with IC50 values of 1.19 similar to 6.13 mu M.