Exocyclically metallated tetrapyridinoporphyrazine as a potential photosensitizer for photodynamic therapy

Abstract

We report the first exocyclically metallated tetrapyridinoporphyrazine, [tetrakis-(trans-Pt(NH₃)₂Cl)-tetra(3,4-pyrido)porphyrazine-zinc(II)](NO₃)₄ (4), synthesized in a multistep synthesis starting from 3,4-pyridinedicarbonitrile (1). The synthetic procedure involved a platination reaction of the intermediate tetra(3,4-pyrido)porphyrazine-zinc(II) (2), whereby the zinc(II) enhanced the solubility of the intermediate enabling the platination reaction. A similar approach to synthesize [tetrakis-(trans-Pt(NH₃)₂Cl)-tetra(3,4-pyrido)porphyrazine](NO₃)₄ (5) failed due to the unsuitable solubility properties of the intermediate tetra(3,4-pyrido)porphyrazine (3). The final product 4 and the intermediates were characterized, the photochemical and photophysical properties were determined and the photocytotoxicities were investigated. We demonstrate that the platinated tetra-pyridinoporphyrazine 4 is a potential photosensitizer for photodynamic therapy (PDT).