Monoterpenoid indole alkaloids from Alstonia scholaris and their Toxoplasma gondii inhibitory activity.

Nine previously unreported various types of monoterpenoid indole alkaloids, together with seven known analogues were isolated from the stem barks of Alstonia scholaris through a silica gel free methodology. The structures of 1-9 were elucidated by spectroscopic data analysis, electronic circular dichroism calculations, and single-crystal X-ray diffraction. Compound 1 is a modified echitamine-type alkaloid with a novel 6/5/5/7/6/6 hetero hexacyclic bridged ring system, and 8 and 9 exist as a zwitterion and trifluoroacetate salt, respectively. The anti-Toxoplasma activity of all isolates on infected Vero cells were evaluated, which revealed that compound 14 at 0.24 μM displayed potent activity. This study expanded the structural diversity of alkaloids of A. scholaris, and presented their potential application in anti-Toxoplasma drug development.