A Chimeric Ligand Approach Leading to Potent Antiprion Active Acridine Derivatives:  Design, Synthesis, and Biological Investigations

Human transmissible neurodegenerations including Creutzfeldt−Jakob disease are unique, since they are caused by prions, an infectious agent that replicates without nucleic acids but instead by inducing conversion of a host-resident normal prion protein to a misfolded conformational isoform. For pharmacotherapy of these unusual diseases, tricyclic heterocyclic compounds such as quinacrine have been considered, but with ambiguous success in vivo, so far. On the basis of the synergistic antiprion effects of quinacrine and iminodibenzyl derivatives, we introduce a novel class of potential pharmaceuticals representing structural chimeras of quinacrine and imipramine analogues. We describe the chemical synthesis and bioassays of a focused library of these compounds. The most potent target compound 2a revealed an EC₅₀ value of 20 nM determined with a cell model of prion disease, thus substantially improving the antiprion efficacy of quinacrine.