Photoinduced Reactions of cis,trans,cis‐[PtIV(N3)2(OH)2(NH3)2] with 1‐Methylimidazole

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Abstract
Lighting up new platinum anticancer complexes: Photoactivation of a platinum(IV) diazido anticancer complex in the presence of a derivative of imidazole, an important constituent of biomolecules, gives surprising photoproducts, including a tetrakis imidazole platinum(II) adduct (see figure), together with free azide, dioxygen and ammonia. The photodecomposition of cis,trans,cis‐[PtIV(N3)2(OH)2(NH3)2] in phosphate buffered saline (PBS), as well as in the presence of 1‐methylimidazole (1‐MeIm), induced by UVA light (centred at λ=365 nm) has been studied by multinuclear NMR spectroscopy. We show that photoreduction, photoisomerisation and trans‐labilisation pathways are involved. The photodecomposition pathway in PBS, which involves azide release, as detected by 14N NMR spectroscopy, appears to differ from that in acidic aqueous conditions, under which N2 is a product. A number of trans‐{N‐PtII‐NH3} species were also observed as photoproducts, as well as the release of free ammonia with a corresponding increase in pH. Oxygen was also detected as a product in solution. In the presence of 1‐methylimidazole, surprisingly the major photoproduct was the tetra‐substituted PtII complex [PtII(1‐MeIm‐N3)4]2+ (structure confirmed by crystallography), even at a Pt/1‐MeIm molar ratio of 1:1, together with cis‐ and trans‐[PtII(NH3)2(1‐MeIm‐N3)2]2+ as minor products. In these photoinduced 1‐MeIm reactions, free ammonia, azide and oxygen were also detected. The results from this study illustrate that photoinduced reactions of platinum complexes can lead to novel reaction pathways, and therefore to new cytotoxic mechanisms in cancer cells.

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