Rupestrisine A and B, two novel dimeric indole alkaloids from Alstonia rupestris

Abstract Rupestrisine A (1), an unprecedented heteroyohimbine-kopsinine type dimeric indole alkaloid, and rupestrisine B (2), the first example of yohimbine-kopsinine type bisindole alkaloid, were isolated from Alstonia rupestris. Their structures were elucidated based on 1D and 2D-NMR, MS, ECD, FTIR and UV spectroscopic data. Compound 1 showed moderate activity of inhibiting NO production of RAW264.7 cells induced by lipopolysaccharide with an IC50 value of 17.5 ± 1.6 μM.