Novel paramagnetic macromolecular complexes derived from the linkage of a macrocyclic Gd(III) complex to polyamino acids through a squaric acid moiety

Macromolecular Gd(III) complexes may find useful application as contrast agents for magnetic resonance angiography (MRA). Herein two novel systems are reported, namely Gd(DO3ASQ)(3)-lys(16) and Gd(DO3ASQ)(30)-orn(114), Their syntheses are based on the ability of the squaric acid moiety to act as a linker between the D03A (1,4,7, 10-tetraazacyclododecane-1,4,7-triacetic acid) chelate moiety and the polyamino acidic chain. Moreover, the squaric acid participates in the coordination cage of the Gd(III) ion. The investigation of H-1 and O-17 NMR relaxation processes of solvent water nuclei allowed a detailed characterization of the systems under study. Gd(DO3ASQ)(30)-orn(114) displays a remarkable ability to enhance the water proton relaxation rate of its solutions, and it. may be considered as potential contrast agent for MRA applications.