A panel of nitro substituted 5,15-diaryl-porphyrins, featuring nitro groups either on the phenyl rings or on one of the two free meso-positions, was synthesized. In the former category, compounds 5-(3-nitrophenyl)-15-phenylporphyrin, 5,15-di(3-nitrophenyl)porphyrin and 5-(4-nitrophenyl)-15-phenylporphyrin were obtained following standard procedures by reacting dipyrromethane and aromatic aldehydes. In the latter category, porphyrins 10-nitro-5,15-diphenylporphyrin, 10-nitro-5-(3-methoxyphenyl)-15-phenylporphyrin and 10-nitro-5,15-di(3-methoxyphenyl)porphyrin were generated by nitration of 5,15-diarylporphyrins with trifluoroacetic acid/sodium nitrite under particularly mild conditions. The new molecules bearing one or two nitro-groups were tested as photosensitizers during in vitro experiments on a human colon adenocarcinoma cell line (HCT116), and their effects were compared with those induced by temoporfin, porfimer sodium and by some previously published electron-rich diarylporphyrins. The results, expressed as IC50 values obtained by the MTT test following 24 h incubation with the photosensitizers and 2 h irradiation with a 500 W tungsten-halogen lamp, indicate that the presence of an electron withdrawing substituent, on a meso-position, decreases the photodynamic activity of the compound. Conversely, 5-(3-nitrophenyl)-15-phenylporphyrin, a non symmetrically substituted diarylporphyrin bearing both one electron-deficient and one lipophilic moiety, resulted in high phototoxic activity.
Porfimer Sodium
