Highly stable acyclic bifunctional chelator for 64Cu PET imaging

Abstract

Abstract Ligand L1, based on a pyridine scaffold, functionalized by two bis(methane phosphonate)aminomethyl groups, was shown to display a very high affinity towards Cu(II) (log K CuL=22.7) and selectivity over Ni(II), Co(II), Zn(II) and Ga(III) (Δ log K ML>4) as shown by the values of the stability constants obtained from potentiometric measurements. Insights into the coordination mode of the ligand around Cu(II) cation were obtained by UV-Vis absorption and EPR spectroscopies as well as density functional theory (DFT) calculations (B3LYP model) performed in aqueous solution. The results point to a pentacoordination pattern of the metal ion in the fully deprotonated [CuL1]6− species. Considering the beneficial thermodynamic parameters of this ligand, kinetic experiments were run to follow the formation of the copper(II) complexes, indicating a very rapid formation of the complex, appropriat e for 64Cu complexation. As L1 represents a particularly interesting target within the frame of 64Cu PET imaging, a synthetic protocol was developed to introduce a labeling function on the pyridyl moiety of L1, thereby affording L2, a potential bifunctional chelator (BFC) for PET imaging.