Three New Cytotoxic Monoterpenoid Bisindole Alkaloids from Tabernaemontana bufalina

Abstract 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 ~ 6.13 µM.