Synthesis of N-acridinyl-N'-alkylguanidines: dramatic influence of amine to guanidine replacement on the physicochemical properties.

Transformation of aminoacridines into N-acridinyl-N'-alkylguanidines is described. The chosen procedure allows introduction of pendent substituents (exemplified by N,N-dimethylaminopropyl chain) into key acridinyl thioureas, thus opening the way to structural diversity. Spectroscopic study and pK(a) determination show that the presence of the strongly basic guanidine has a dramatic influence on the ionization of the acridine nucleus by lowering the pk(a) value down to 4.49.