Synthesis of a tricyclic tetraazatriacetic ligand for gadolinium(III) as potential contrast agent for MRI

A tricyclic tetraazatriacetic compound, which is a rigidified derivative of PCTA12 ligand with a cyclohexylene bridge replacing an ethylene one, was prepared. Two synthetic routes have been investigated, both of them implying a common functionalized triamine intermediate. Whatever the route, four synthetic steps were necessary to obtain the target tricyclic ligand. The more effective one (Route B) led to the desired compound in 19% overall yield from the triamine intermediate. The corresponding gadolinium complex of 1/1 stoichiometry was then prepared in order to evaluate it as potential contrast agent for MRI.