Gadobenic acid

Gadobenic acid is a complex of gadolinium with the ligand BOPTA. In the form of the diglumine salt it functions as a gadolinium-based MRI contrast medium, under the trade name gadobenate dimeglumine.

BOPTA is a derivative of DTPA in which one terminal carboxyl group, –C(O)OH is replaced by -C–O–CH₂C₆H₅. Thus gadobenic acid is closely related to gadopentetic acid. BOPTA itself was first synthesized in 1995. ^[1] In the "gadobenate" ion gadolinium ion is 9-coordinate with BOPTA acting as a 8-coordinating ligand. The ninth position is occupied by a water molecule, which exchanges rapidly with water molecules in the immediate vicinity of the strongly paramagnetic complex, providing a mechanism for MRI contrast enhancement. ¹³⁹La NMR studies on the diamagnetic La-BOPTA^2- complex suggest that the Gd complex maintains in solution the same kind of coordination as found, by X-ray crystallography, in the solid state for Gd-BOPTA disodium salt.^[1]