A library of functionalized 6-chloro-2-methoxy-(N(9)-substituted)acridin-9-amines structurally related to quinacrine were synthesized and evaluated for antiprion activity on four different cell models persistently infected with scrapie prion strains (ScN2a, N167, Ch2) or a human disease prion strain (F3). Most of the compounds were distinguished by the side chain attached to 9-amino of the acridine ring. These were dialkylaminoalkyl and phenyl with basic groups on the phenyl ring. The most promising compound was 6-chloro-2-methoxy-N-(4-(4-methylpiperazin-1-yl)phenyl)acridin-9-amine (15) which had submicromolar EC(50) values (0.1-0.7microM) on all cell models, was able to clear PrP(Sc) at non-toxic concentrations of 1.2-2.5microM, and was more active than quinacrine in terms of EC(50) values. Other promising compounds were 14 (a regioisomer of 15) and 17 which had a 1-benzylpiperidin-4-yl substituent attached to the 9-amino function. Activity was strongly dependent on the presence of a substituted acridine ring, which in this library comprised 6-chloro-2-methoxy substituents on the acridine ring. The side chains of 14, 15, and 17 have not been previously associated with antiprion activity and are interesting leads for further optimization of antiprion activity.