Synthesis of Magnetic Resonance Imaging Contrast Agent with Tethered Quaternary Ammonium Group

Benefited with the high water solubility of quaternary ammonium group, a magnetic resonance imaging (MRI) contrast agent with tethered quaternary ammonium group linked by long alkyl chain was synthesized. The quaternary ammonium group was introduced in the skeleton of 1,4,7,10 tetraazacyclododecane (cyclen), and four secondary amino groups in cyclen were functionalized with carboxymethyl groups, forming a polychelating ligand with a quaternary ammonium side chain. Without affecting the conjugation ability, this ligand forms stable Gd(III) complex showing higher relaxivity than Gd(III) DOTA. With both quaternary ammonium group and long alkyl chain installed in the same molecule, further functionalization or modification to achieve high performance MRI contrast agents is promising.