| Resumo: | The synthesis and characterization of a new class of DTPA bisamide-linked glycoconjugates of different sugars (lactose, Lac, and galactose, Gal) and valencies (di and tetra) and their Ln(III) complexes is reported. The 1H NMR spectra of the Sm(III) and Eu(III) complexes of DTPAGal2, DTPAGal4, and DTPALac2 obtained between 7 and 80 ºC, indicate that most (if not all) of the four possible diastereoisomeric pairs of structures, resulting from the chirality of the three bound DTPA nitrogen atoms, are present in solution, with different relative populations. The dynamic effects of racemization of the central nitrogen on the NMR spectra show that this process is in fast exchange at 60 ºC for the Sm(III) complexes and in slow exchange at 7 ºC for the Eu(III) complexes. The in vitro r1 nuclear magnetic relaxation dispersion (NMRD) of the water protons of the Gd(III)-DTPA bis-amide glycoconjugate containing two lactosyl moieties, Gd(III)-DTPALac2, was studied, yielding the molecular parameters that govern its relaxivity. Its r1 value, at 25 oC and 20 MHz, is 13% higher than that reported for Gd(III) chelates of lower molecular weight DTPA-bisamides, such as DTPA-BMA, consistent with a five times longer tau-R value. The water exchange rate, kex, and the electron spin relaxation parameters of the Gd(III)-DTPALac2 complex are within the usual range for similar Gd(III)-DTPA bisamide chelates.
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