Gd-Complexes of DTPA-bis(amides) Functionalized by Pyridine and Picolinamide: Synthesis, Thermodynamic Stability, and Relaxivity Properties

A series of DTPA-bis(amides) functionalized by pyridine (1a-c) and N-phenylpicolinamide) (1d-e) and their Gd(III)-complexes of the type [Gd(1)(H2O)]·xH2O (2a-e) were prepared and characterized by analytical and spectroscopic techniques. Potentiality of 2a-e as contrast agents for magnetic resonance imaging (MRI CA) was investigated by measuring relevant physicochemical properties and relaxivities and compared with [Gd(DTPA-BMA)(H2O)] (DTPA-BMA = N,N''-di(methylcarbamoylmethyl)diethylenetriamine-N,N',N''-tri-acetate) (OmniscanR). The R1 relaxivities of aqueous solutions of 2a-c are in the range of 3.33-5.02 mM−1sec−1, which are comparable with those of OmniscanR (r1 = 4.58 mM−1sec−1). Complexes 2d-e, insoluble in water, exhibit relatively higher R1 values (8.1- 8.3 mM−1sec−1) in HP-β-CD solutions. Key Words: MRI CA, Gd(DTPA-bisamide), Pyridine, Picolinamide, T1 relaxivit