An alkaloid with novel skeleton, sinoscrewtine (1), has been isolated from the roots of Sinomenium acutum. Its structure was established by spectral analysis and X-ray crystallographic study, and its possible biosynthetic pathway was delivered. In vitro experiments, 1 showed weak injurious effects against H2O2/Aβ25-35 induced oxidative injury in PC-12 cells and DPPH radical scavenging activity with IC50 of 32.6 μM. © 2012 Elsevier B.V.