Two di-nuclear non-ionic MRI contrast agents, (Gd-DO3A)2-BMQX and (Gd-DO3A)2-BMP, have been designed and synthesized by fusing the DO3A units together with a quinoxalinyl or pyrazinyl moiety. They have improved longitudinal relaxivities of 5.23 and 5.16 mM Gd−1 s−1, respectively, at 20 MHz magnet, 37 °C and pH 7.0. In addition, they possess high thermodynamic stability and kinetic inertness. The cytotoxicity studies indicated that the toxicity of these two agents were low. All these properties satisfy the requirements for clinical applications.
