Macroline–Sarpagine Bisindole Alkaloids with Antiproliferative Activity from Alstonia penangiana

A methanol extract of the stem bark of the Malayan Alstonia penangiana provided seven new bisindole alkaloids, comprising six macroline–sarpagine alkaloids (angustilongines E–K, 1–6) and one macroline–pleiocarpamine bisindole alkaloid (angustilongine L, 7). Analysis of the spectroscopic data (NMR and MS) of these compounds led to the proposed structures of these alkaloids. The macroline–sarpagine alkaloids (1–6) showed in vitro growth inhibitory activity against a panel of human cancer cell lines, inclusive of KB, vincristine-resistant KB, PC-3, LNCaP, MCF7, MDA-MB-231, HT-29, HCT 116, and A549 cells (IC50 values: 0.02–9.0 μM).