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Synthesis and Relaxation Properties of Three Novel Bis-macrocycles: Attempt towards Calcium Sensitive MRI Contrast Agents

MR contrast agents whose efficiency depends on the concentration of signaling molecules may be used to directly visualize neuronal activation. The so-called ‘smart’ contrast agents for magnetic resonance imaging exhibit dynamic and reversible modulation of their relaxivity by specific physiological or biochemical triggers such as changes in pH, Ca concentration or enzymatic activity. The extracellular concentration of Ca plays an important role in the physiological and pathological processes of the nervous system; it led us to design chelating systems in which the relaxivity is influenced by the Ca concentration. We synthesized three novel bifunctional bismacrocycles based on DO3A-EA coupled to EDTA/DTPA-bisanhydride via amide bonds.