Macroline–Sarpagine Bisindole Alkaloids with Antiproliferative Activity from <i>Alstonia penangiana</i>

Abstract

A methanol extract of the stem bark of the Malayan <i>Alstonia penangiana</i> provided seven new bisindole alkaloids, comprising six macroline-sarpagine alkaloids (angustilongines E-K, <b>1</b>-<b>6</b>) and one macroline-pleiocarpamine bisindole alkaloid (angustilongine L, <b>7</b>). Analysis of the spectroscopic data (NMR and MS) of these compounds led to the proposed structures of these alkaloids. The macroline-sarpagine alkaloids (<b>1</b>-<b>6</b>) 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).