Four Alkaloids from <i>Alstonia scholaris</i> with Antitumor Activity via Disturbing Glutathione Homeostasis

Alstoschoquinolines A–D (1–4) representing three unprecedented scaffolds were isolated from the leaves of Alstonia scholaris through direct separation by LC/MS detection. 1 and 2 consisted of a 5/6/5-coupled quinoline architecture containing six consecutive chiral carbons, while 3 and 4 possessed a bridged ring featuring 6/6/6/6 and 6/6/8/6 skeletons, respectively. They might be derived from the corynantheine-type indole alkaloid via sequential oxidation and rearrangement. Compound 3 exhibited a significant inhibitory effect on colon carcinoma cells by disturbing glutathione circulation.