Four Alkaloids from Alstonia scholaris 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.