Novel water-soluble (99m)Tc(I)/Re(I)-porphyrin conjugates as potential multimodal agents for molecular imaging

The synthesis and characterization of two novel water soluble porphyrins with three meso pyridyl rings and one peripheral chelator - either a diethylenetriamine unit (4) or a bipyridyl fragment (8) - for binding to the {(99m)Tc(CO)3}(+) moiety is reported. In 8, despite the presence of a flexible and hydrophilic PEG-like linker that connects the bpy unit to the macrocycle, good water solubility was only obtained by methylation of the pyridyl N atoms that provided three extra positive charges. Furthermore, the water-soluble conjugates of 4 and 8 with either one fac-{Re(CO)3}(+) (9 and 10, respectively) or one fac-{(99m)Tc(CO)3}(+) fragment (9a and 10a, respectively) are described.