Inulin as a carrier for contrast agents in magnetic resonance imaging

Magnetic resonance angiography (MRA) has put forth an impetus for the development of macromolecular Gd-III complexes that have a prolonged lifetime in the vascular system. Herein, we report the synthesis and Gd-III complexation of a new sugar conjugate based on inulin and the DO3A ligand (DO3A = 1,4,7,10-tetraazacyclododecan1,4,7-triacetic acid). Two API-DO3ASQ conjugates (API = 0-(aminopropyl)inulin, SQ = squaric acid = 3,4-dihydroxy-3cyclobutene-1,2-dione) with different degrees of substitution (ds=0.7 and ds=1.5) were prepared from API by using the diethyl ester of squaric acid as a linking agent for the DO3A chelate. The efficacies of the resulting Gd-III compounds were evaluated by investigation of their water H-1 longitudinal- relaxation-rate enhancements at variable field (NMRD). A dramatic increase in relaxivity was observed in the more highly substituted conjugate (ds = 1.5); this prompted us to do a variable-temperature 170 study in order to further characterize the relaxation parameters involved in this system. [Gd(APIDO3ASQ)] shows promising properties for application as a contrast agent for MRI.