Novel porphyrin-Schiff base conjugates: synthesis, characterization and in vitro photodynamic activities

Three novel porphyrin-Schiff base conjugates derived from tetra(4-aminophenyl)porphyrin (TAPP), namely, tetra[4-(4-hydroxy benzylideneamino)]phenyl porphyrin (3a), tetra[4-(2-thienyldeneamino)]phenyl porphyrin (3b) and tetra[4-(2-pyridyldeneamino)]phenyl porphyrin (3c), were synthesized and characterized by IR, UV-vis, H-1 NMR, HRMS and elementary analysis. Their biological activities against human epidermoid carcinoma (A431) cells were evaluated with an MTT assay. As we expected, the porphyrin conjugates showed negligible cytotoxicity to A431 cells in the absence of light, while their phototoxic activities were improved after irradiated with LED lamp (425 nm) and increased significantly with increased doses. The fluorescence microscope pictures revealed that the three porphyrin-Schiff conjugates could diffuse into skin cancer cells, demonstrating that these compounds are potential candidates for photodynamic therapy agents.