Enhanced relaxivity of GdIII-complexes with HP-DO3A-like ligands upon the activation of the intramolecular catalysis of the prototropic exchange

Gadolinium(III) complexes have been employed for more than 30 years as contrast agents in magnetic resonance imaging (MRI). In order to further improve the diagnostic accuracy of enhanced magnetic resonance images or to provide comparable enhancement at a reduced administered dose, current research is focusing on the development of GdIII-complexes characterized by higher relaxivity. In this study we describe the synthesis and the equilibrium, kinetic, relaxation and structural properties of two new GdIII-complexes based on modified 10-(2-hydroxypropyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (HP-DO3A) structure which, due to an intramolecular prototropic exchange, display more than two-fold higher relaxivity compared to currently available GdIII-based MRI contrast agents.