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.  In the "gadobenate" ion gadolinium ion is 9-coordinate with BOPTA acting as an 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-BOPTA2− 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.
^ abUggeri, F.; Aime, S., Anelli, P.L., Botta, M., Brocchetta, M., De Haën, C., Ermondi, G., Grandi, M., Paoli, P. (1995). "Novel contrast agents for magnetic resonance imaging. Synthesis and characterization of the ligand BOPTA and its Ln(III) complexes (Ln = Gd, La, Lu). X-ray structure of disodium (TPS-9-145337286-C-S)-[4-carboxy-5,8,11-tris(carboxymethyl)-1-phenyl-2-oxa-5,8, 11-triazatridecan-13-oato(5-)]gadolinate(2-) in a mixture with its enantiomer". Inorg. Chem.34 (3): 633–642. doi:10.1021/ic00107a017.