Exploring the binding of amine and sulfonamide ligands in Rhenium(I) Tricarbonyl and Platinum(II) complexes
Platinum is the metal present in various classes of inorganic medicinal agents directed at important diseases such as cancer or viral infections. Several new Pt(II) complexes of polyamine ligands bearing a dansyl moiety linked by a sulfonamide group were prepared; in some cases the sulfonamide nitrogen formed a bond to Pt. The sulfonamido group donates strongly to Pt and places the dansyl group close to a vacant coordination position, allowing it to stack with bound guanine base (G) when G binds. The emission of the fluorophore decreases with decreasing distance to Pt. Metal nuclide radiopharmaceuticals contain a metal core and an inner ligating unit, usually having chelate rings. The development of the advantageous fac-[99mTc(CO)3(H2O)3]+ precursor has opened new directions for radiolabeling. The non-radioactive fac-[Re(CO)3(H2O)3]+ analogue is useful in understanding the chemistry of agents derived from the [99mTc(CO)3(H2O)3]+ species. To achieve a net neutral coordination unit in radiopharmaceuticals with a fac-M(CO)3+ core (M = Tc, Re), facially coordinated monoanionic tridentate ligands (L-) are needed. Several fac-[Re(CO)3L] complexes containing the sulfonamido group as one terminal ligating group were synthesized and characterized by X-ray crystallography and NMR spectroscopy. For most sulfonamido complexes studied here, the two chelate rings have different pucker chirality, as is commonly found for a broad range of metal complexes. The complexes are stable at neutral and basic pH values and thus have potential for providing a neutral label in radiopharmaceuticals. The NMR signal averaging indicates that the rotations about the N-S and S-C bonds of the sulfonamido group are rapid on the NMR time scale. Understanding the chemical features of the prototypical complexes by using the fac-[Re(CO)3L]-analogue approach and the minimal ligand was the goal of this part of this investigation. fac-[Re(CO)3L]+ complexes containing prototypical NNN or NSN tridentate ligands, such as diethylenetriamine (dien) and simple dien derivatives, were investigated by X-ray crystallographic and NMR methods. fac-[Re(CO)3L]+ complexes with two terminal exo-NH groups exhibit unusually upfield exo-NH NMR signals, which shift downfield on addition of Cl- indicating 1:1 ion pairs forms involving one Cl- to two exo-NH's H-bonds.
rhenium tricarbonyl, platinum, sulfonamide ligands
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