Oxidized Derivatives of Macroline, Sarpagine, and Pleiocarpamine Alkaloids from <i>Alstonia angustifolia</i>

A total of 20 new indole alkaloids comprising mainly oxidized derivatives of macroline- (including alstofonidine, a macroline indole incorporating a butyrolactone ring-F), pleiocarpamine-, and sarpagine-type alkaloids were isolated from the bark and leaf extracts of <i>Alstonia angustifolia.</i> The structures and relative configurations of these alkaloids were determined using NMR and MS analyses and in some instances confirmed by X-ray diffraction analyses. Alkaloids <b>3</b>, <b>7</b>, <b>35</b>, and <b>41</b> showed moderate to weak activity, while <b>21</b> showed strong activity in reversing multidrug resistance in vincristine-resistant KB cells