A phytochemical investigation of Menispermum dauricum led to the isolation of five oxoisoaporphine-type alkaloids (1–5) and five aporphine-type alkaloids (6–10), including a novel oxoisoaporphine-type alkaloid: menispeimin A (1). Their structures were elucidated by spectroscopic studies including MS, 1 D and 2 D NMR, and confirmed by comparing with literature data. Among them, alkaloids 4–10 were obtained for the first time from Menispermum genus. Natural products 2, 4 and 6 exhibited significant cytotoxic activity against A549,...