Synthesis of Bimodal Magnetic Resonance Imaging Contrast Agent from Tris(2-aminoethyl)amine and 6-Carboxy-Fluorescein

A fluorescent ligand with polydentate amino carboxylate moieties was synthesized from tris(2-aminoethyl)amine and benzyl 2-bromoacetate,followed by the introduction of fluorescent functionality through an amidation reaction between the primary amine group and 6-carboxy-fluorescein.After coordination with paramagnetic GdC1₃·6H₂O,a bimodal contrast agent combing the ability for magnetic resonance imaging (MRI) and optical imaging was formed.The structures of the ligands and the complexes were confirmed by both H- and C-NMR、high resolution mass spectrometry,and ICP-AES.This new MRI contrast agent showed a r₁ value (longitudinal relaxivity) of 3.46 mM^-1·s^-1,comparable to commercial small molecular contrast agent like Magevist^®(Gd-DTPA).This complex also showed bright green fluorescence when shined with UV light,showing a high quantum yield of 66%,which is essential for clinical bimodal imaging.