Relaxivity study and x-ray structure of Gd(III)-diethylenetriamine-N,N',N''-triacetic-N,N''-bis(benzylamide). A potential MRI contrast agent

The new bis(amide) derivatives of DTPA (diethylenetriamine-N,N,N',N '',N ''-pentaacetic acid), diethylenetriamine-N,N',N ''-triacetic-N,N ''-bis(benzylamide) (DTPA-BBA) have been synthesized. The crystal structure of gadolinium(III) complex of DTPA-BBA ([Gd(DTPA-BBA)]) has been determined by X-ray crystallography: C28H52GdN5O17, M-w = 889 g mol(-1), space group P (1) over bar (#2) (triclinic), a = 12.645(4), b = 14.125(8), c = 12.623(4) Angstrom, alpha = 111.60(3), beta = 114.79(3), gamma = 88.39(4)degrees, V = 1881(1) Angstrom(3), Z = 2, D-x = 1.569 g/cm(3), lambda(Mo K alpha) = 0.71069 Angstrom, mu = 18.44 cm(-1), final R = 0.047, R-w = 0.046 for 3755 independent observed reflections at 23 degrees C. The coordination sphere of Gd(III) comprises three amine nitrogens, two amide oxygens, three carboxylic acid oxygens, and one water. The relaxivitiy of Gd(III) complex was determined to be R1 = 4.08(4) and R2 = 6.06(5) dm(3) mmol(-1) s(-1) at pH = 7.0, 20 MHz, and 37(1)degrees C. Additionally, the R1 relaxivity for Gd(III) chelate was found to be invariant with respect to pH changes over the range of 2-10. This indicates that a constant inner-sphere hydration number is associated with the [Gd(DTPA-BBA)] complex. Hence the high stability of the complex is demonstrated.