TOWARDS NOVEL NONIONIC CONTRAST AGENTS FOR MAGNETIC-RESONANCE-IMAGING- SYNTHESIS AND CHARACTERIZATION OF [(BISPHENYLAMIDE-DTPA)M(III)] COMPLEXES (M=LU, Y AND GD)

The synthesis and the acid-base behaviour of a novel DTPA-like ligand, III, containing two phenylamido functionalities are reported. Upon co mplexation with Lu(III) and Y(III), bisphenylamide-DTPA (BPhA-DTPA) ac ts as an octadentate ligand. Both complexes are present in solution un der three of the four possible conformers. In the case of the Lu(III) complex, a dynamic behaviour has been observed by increasing either th e temperature or the pH of the solution. In the. H-1 NMR spectrum of t he Y(III) complex in methanol-d(4) solution the direct observation of a coordinated water molecule and of its exchange process with the free water proved possible. The ability of Gd-BPM-DTPA to enhance the wate r proton relaxation rate (relaxivity 4.17 s(-1)) is comparable to that of the parent [Gd-DTPA](2-) and other related complexes. On the basis of the knowledge of its relaxivity it has been possible to determine the formation constant (K-f = 6.12x10(16)) by measuring the water prot on relaxation times of solutions containing the ligand LII and variabl e amounts of [Gd-EDTA](-). Being Gd-BPhA-DTPA a potential contrast age nt for Magnetic Resonance Imaging, the relaxometric properties of its aqueous solutions have been investigated more deeply by measuring the 1/T-I Nuclear Magnetic Relaxation Dispersion profile over an extended range of magnetic field strength. The analysis of this profile afforde d an unexpectedly long value for the exchange lifetime tau(M) (1.47 mu s at 25 degrees C) whereas the other parameters relevant to the relax ation process are very similar to those previously found for the paren t [Gd-DTPA](2-) complex.