Three new monoterpenoid indole alkaloids from Alstonia rostrata

Abstract Three new monoterpenoid indole alkaloids, alstratines A–C (1–3), along with three known ones were isolated from Alstonia rostrata. Compound 2 is the first example of an akuammicine-type alkaloid possessing an unprecedented 6/5/6/5/6/5 hexacyclic ring system. The new structures including their absolute configurations were elucidated on the basis of comprehensive spectroscopic data analyses, computational calculation methods, and X-ray diffraction analysis. Compound 2 exhibited potent vasorelaxant activity with an EC50 value of 6.3 μM. In addition, compound 5 exhibited moderate acetylcholinesterase (AChE) inhibitory activity with an IC50 value of 26.8 μM.