RELAXIVITY STUDY AND X-RAY STRUCTURE OF TRIAMINE-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 struct ure of gadolinium(III) complex of DTPA-BBA ([Gd(DTPA-BBA)]) has been d etermined by X-ray crystallography: C28H52GdN5O17, M-w = 889 g mol(-1) , space group P (1) over bar (#2) (triclinic), a = 12.645(4), b = 14.1 25(8), c = 12.623(4) Angstrom, alpha = 111.60(3), beta = 114.79(3), ga mma = 88.39(4)degrees, V = 1881(1) Angstrom(3), Z = 2, D-x = 1.569 g/c m(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 n itrogens, two amide oxygens, three carboxylic acid oxygens, and one wa ter. 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 f ound to be invariant with respect to pH changes over the range of 2-10 . This indicates that a constant inner-sphere hydration number is asso ciated with the [Gd(DTPA-BBA)] complex. Hence the high stability of th e complex is demonstrated.