Indole alkaloids with antibacterial activity from aqueous fraction of Alstonia scholaris

Eleven new indole alkaloids, alstoniascholarines A–K (1–11), along with one known analogue, were isolated from the aqueous fraction of Alstonia scholaris leaf extract. Their structures were established on the basis of extensive spectroscopic data analysis, chemical transformation, and quantum theory. Alkaloid 4 possessed a novel skeleton with fused-ring and a six-membered ring, the absolute configuration of which was assigned by quantum theory. Alkaloids 6 and 10 showed the best antibacterial activity against Pseudomonas aeruginosa with an MIC value of 3.13 μg/mL.

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