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: C 28 H 52 GdN 5 O 17 , M w = 889 g mol −1 , space group \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm P}\bar 1 $\end{document} (#2) (triclinic), a = 12.645(4), b=14.125(8), c = 12.623(4) Å, α = 111.60(3), β = 114.79(3), γ = 88.39(4)°, V = 1881(1) Å 3 , Z = 2, D x = 1.569 g/cm 3 , λ(Mo Kα) =0.71069 Å, μ = 18.44 cm −1 , final R = 0.047, R w = 0.046 for 3755 independent observed reflections at 23 °C. The coordination sphere of Gd(III) comprises three amine nitrogens, two amide oxygens, three carboxylic acid oxygens, and one water. The relaxivity 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) °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.