Tetra-2,3-pyrazinoporphyrazines with externally appended pyridine rings. 11. Photoactivity of a new Pt(II) pentanuclear macrocycle bearing four cisplatin-like functionalities and its related monoplatinated species

The pentanuclear Pt(II) porphyrazine compound [(PtCl(2))(4)LPt] (L = tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazinato dianion), the mononuclear species [LPt] and the octacation [L'Pt](8+) (neutralized by I-ions; L' = L octaquaternized at the pyridine N atoms) were synthesized and characterized by IR/UV-visible spectral measurements. (1)H and (13)C NMR spectral data on [(PtCl(2))(4)LPt] indicate that the four PtCl(2) units are coordinated at the pyridine N atoms of the peripheral dipyridinopyrazine fragments ("py-py" coordination) and the largely prevalent conformational arrangement of the entire macrocycle, established to have the external N(2(py))PtCl(2) coordination sites all oriented on the same side with respect to the plane of the central porphyrazine framework, closely recalls that which was previously defined for the related Pd(II) analog [(PdCl(2))(4)LPd]. The currently investigated triad of Pt(II) macrocycles, like the related Pd(II) species, behave as photosensitizers for the generation of singlet oxygen, the cytotoxic agent active in photodynamic therapy (PDT). A bimodal anticancer potentiality is expressed by the pentaplatinated compound, [(PtCl(2))(4)LPt], which represents an unprecedented example of a multifunctional drug due to the presence of four contiguous cisplatin-like functionalities.