Gold(I) Complexes Incorporating Emissive Mercapto-Pteridine Ligands: Syntheses, X-ray Structure, Luminescence and Preliminary Cytotoxic Evaluation

The syntheses of six new mixed P/S-donor two-coordinate AuI complexes are described. The complexes incorporate a pteridinyl ligand coordinated through a thiolate donor, and an ancillary tertiary phosphane (PPh3 or PCy3). The mercapto-pteridine ligands (L1L3) differ in the nature of the substituents on the pteridine core. An X-ray crystal structure was obtained for one of the examples, [(L1)Au(PPh3)], revealing weak intermolecular interactions between two molecules of the complex: pp contacts between aromatic rings appear to support an intermolecular AuAu contact of approximately 3.05 angstrom. All of the complexes are luminescent in solution, with emission arising from tuneable ligand-based excited states, and characterised as a perturbed fluorescence in nature. In this context, complexes of L3 displayed useful visible absorption and emission. Preliminary cytotoxicity assessments were conducted using the MTT assay, and the complexes each displayed impressive anti-proliferative activities (IC50 < 5 mu M) with respect to four different adenocarcinoma cell lines (MCF7, A549, PC3 and LOVO). For a given pteridine moiety, triphenylphosphane appeared to be the co-ligand of choice for enhancing biological activity.