From the leaves of a yet undescribed Congolese Ancistrocladus species, two novel naphthylisoquinoline dimers, spirombandakamines A(1)(1) and A(2) (2), were isolated, together with a new, but classical dimer, mbandakamine B, (3). The cage-like stereostructures of 1 and 2 were established by combining spectroscopic, chemical, and chiroptical methods with quantum -chemical ECD calculations. Their unique molecular frameworks may originate from open-chain dimers, such as 3, by an oxidation-induced cascade of reactions. They possess strong antiprotozoal properties.