Series of 6-aminophenanthridines and related heterocyclic compounds such as benzonaphtyridines were prepared. Reduction of one of the three aromatic rings was also performed. The compounds were first tested for their antiprionactivity in a previously described yeast-based colourimetric prion assay. The most potentderivatives were then assayed ex vivo against the mammalian prion PrPSc in a cell-based