Binuclear gadolinium(III) complex based on DTPA and 1,3-bis(4-aminophenyl)adamantane as a high-relaxivity MRI contrast agent

A novel dimeric gadolinium(III) complex, bis(4-Gd-DTPA-aminophenyl)adamantane ( 5 ), was successfully synthesized using bis(4-aminophenyl)adamantane to link two Gd-DTPA units. All the intermediates and bis(4-Gd-DTPA-aminophenyl)adamantane ( 5 ) have been characterized by 1 H NMR, 13 C NMR, ES-API-MS, HR-ESI-MS, FT-IR and elemental analysis (EA). The longitudinal relaxivity of bis(4-Gd-DTPA-aminophenyl)adamantane is 8.43 mM −1  Gd −1  s −1 at 0.43 T (32 °C, pH 7.0), and 4.89 mM −1  Gd −1  s −1 at 3.0 T (32 °C, pH 7.4). The T 1 -weighted imaging in vitro showed that bis(4-Gd-DTPA-acetylaminophenyl)adamantane can enhance the contrast of images distinctly. But most of all, the kinetic inertness of bis(4-Gd-DTPA-aminophenyl)adamantane ( 5 ) was comparable to that of [Gd(DTPA)(H 2 O)] 2− (Magnetvist®). Moreover, cytotoxicity tests indicated that the bis(4-Gd-DTPA-acetylaminophenyl)adamantane exhibited low toxicity to healthy liver cells (L-02 cells). These results demonstrate that the Gd(III) complex 5 may be a promising MRI contrast agent candidate.