Synthesis of a rigidified bicyclic AAZTA-like ligand and relaxometric characterization of its Gd^III complex

The synthesis of a novel constrained polydentate ligand CpAAZTA derived from the heptadentate polyaminocarboxylic ligand AAZTA (6-amino-6-methylperhydro-1,4-diazepine-N, N’,N’’,N’’-tetraacetic acid) in which the ethylene bridge of the 1,4-diazepine ring is replaced by a cyclopentyl bridge is reported. In order to compare the effect of the different size and rigidity induced on the chelate by a 5-membered ring vs. a previously-reported cyclohexane-derivative, the relaxivity of the corresponding bis-hydrated Gd^III complex was also investigated as a function of the magnetic field, temperature and pH.