Non-ionic Ln(III) chelates as MRI contrast agents: Synthesis, characterisation and 1H NMR relaxometric investigations of bis(benzylamide)diethylenetriaminepentaacetic acid Lu(III) and Gd(III) complexes

Abstract

The syntheses of the ligand bis(benzylamide)diethylenetriaminepentaacetic acid (BBA-DTPA) and its Gd(III) and Lu(III) complexes are reported. The solid state structure of Lu(III) BBA-DTPA was determined in a single crystal X-ray diffraction study. The lutetium ion adopts a mine-coordinate geometry, which is best described as a distorted tricapped prism. Eight coordination sites are occupied by the ligand (three nitrogen atoms, two carboxamide oxygens and three carboxylate oxygens) and the ninth site is occupied by the oxygen atom of a water molecule. The VT 13C NMR spectra of Lu(III) BBA-DTPA are consistent with the presence of three isomers in solution. Water proton relaxation rates have shown that Gd(III) BBA-DTPA displays an analogous behaviour to that observed for other Gd(III) complexes of related bisamide derivatives of DTPA. The solubility of Gd(III) BBA-DTPA has been markedly improved by the presence of an excess of hydroxypropyl-β-cyclodextrin. The thermodynamic stability of the inclusion complex has been evaluated by measuring the proton relaxation enhancement upon addition of β-cyclodextrin.