Anti‐Inflammatory Monoterpene Indole Alkaloids From Alstonia mairei

ABSTRACT 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 IC 50 values ranging from 4.4 to 20.4 µM.