New N-oxide alkaloids from the stems of Sinomenium acutum

Six new alkaloids (1–6) and six known alkaloids (7–12) were obtained from the stems of Sinomenium acutum. Among them, compounds 1–3 and 6 were four N-oxide alkaloids. The structures and absolute configurations of these new alkaloids were elucidated through comprehensive data of 1D and 2D NMR, HRESIMS and ECD spectra. All isolated compounds were evaluated in vitro for their inhibitory activities against nitric oxide (NO) production and inhibitory effects on AChE. Among them, the sinomenine N-oxide (9) was the most potent NO production inhibitor, with an IC50 value of 23.04 μM.