Structures of stemoxazolidinones A–F, alkaloids from Stemona sessilifolia

Six new alkaloids, stemoxazolidinones A–F, were isolated from the roots of Stemona sessilifolia (Miq.) Miq. (Stemonaceae). The structures of stemoxazolidinones A–C, and E were determined by interpretation of their spectroscopic data and those of stemoxazolidinones D and F by X-ray crystallography. These alkaloids possess a novel structural unit in which an oxazolidin-2-one unit fuses with a pyrrolo[1,2-a]azepine nucleus of the rearranged or normal tuberostemonine-type skeleton.