Guatteria species (Annonaceae) are rich in isoquinoline alkaloids that contain a restricted beta phenethylamine moiety and thus have potential monoamine oxidase (MAO) inhibitor for treatment of Alzheimer´s and Parkinson´s diseases. Three aporphine alkaloids have bee isolate from G. stenopelata, the know oxoaporphine dicentrinone (1), and two novel compounds, N-methyldicentrinone (2) and 4,5-dioxodehydrodixentrine (3). Their inhibitory effects on MAO-B were evaluated, but none of them was significantly active.