Anti-Inflammatory Monoterpene Indole Alkaloids From Alstonia mairei

Twelve monoterpene indole alkaloids (1‒12), classified into six diverse types, ajmalicine (1, 3, and 4), tubotaiwine (2), aspidosperma (5 and 6), peraksine (7 and 8), eburnane (9 and 10), and heteroyohimbine (11 and 12), respectively, were isolated from the branches and leaves of Alstonia mairei. Their structures were elucidated via the spectroscopic data interpretation, electronic circular dichroism calculations, single crystal X-ray diffraction analysis, and comparison with literature. Notably, mareines C (1) and D (2) represent the first examples of the natural ajmalicine alkaloid possessing an additional carbon connecting with C-3 and 12-hydroxytubotaiwine alkaloid, respectively. Compounds 3 and 6‒12 were obtained from Alstonia mairei for the first time. In addition, all isolates were evaluated for their anti-inflammatory activities in vitro, and compounds 1, 4, 7/8, 11, and 12 exhibited potent inhibitory activities on the lipopolysaccharide-induced nitric oxide production in RAW264.7 mouse macrophages with IC₅₀ values ranging from 4.4 to 20.4 µM.