Novel β-functionalized mono-charged porphyrinic derivatives: Synthesis and photoinactivation of Escherichia coli

An efficient synthetic approach to mono-cationic porphyrins bearing imidazole and perimidine units at β-pyrrolic positions is described. The procedure giving access to the neutral precursors showed to be more efficient in the presence of a zirconium-based catalyst. These target compounds were in general isolated in good to excellent yields being accompanied with imine type derivatives. The quaternization of the imidazole or perimidine units was performed in the presence of dimethyl sulphate; the mono-charged derivatives were obtained in almost quantitative yields. Some of the new cationic porphyrin derivatives showed to be highly efficient singlet oxygen generators. In biological studies, the mono-cationic porphyrins demonstrated to be able to photoinactivate the bioluminescent E. coli, a Gram-negative model, and the antimicrobial activity showed to be dependent on the structural features of the PS.