Cage-like monoterpenoid indole alkaloids with antimicrobial activity from Alstonia scholaris

Three new cage-like monoterpenoid indole alkaloids, scholarisines T-V (1-3), together with three known analogues 4-6 were isolated from the leaves of Alstonia scholaris. Among them, 2 represents a unique degraded derivative, whereas 3 shares a rare 5,16-seco lactone scaffold. The structures were mainly established by extensive spectroscopic data analyses, and their plausible biosynthesis pathway from picrinine were proposed. Compared with positive control cefotaxime, alkaloid 2 showed remarkable antibacterial activity against Bacillus subtilis with an MIC value of 3.12 mu g/mL, whereas 1-3 exhibited significant antibacterial effects on Escherichia coli with an MIC value of 0.78 mu g/mL. (C) 2018 Published by Elsevier Ltd.