Novel water-soluble 99mTc(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 {99mTc(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-{99mTc(CO)3}+ fragment (9a and 10a, respectively) are described.

Graphical abstractThe synthesis and characterization of two novel water soluble porphyrins bearing one peripheral chelator — either a diethylenetriamine unit (4) or a bipyridyl fragment (8) — in meso position and of their conjugates with either one fac-{Re(CO)3}+ (9 and 10, respectively) or one fac-{99mTc(CO)3}+ fragment (9a and 10a, respectively) are described.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Two porphyrins for binding the {99mTc(CO)3}+ moiety were prepared and characterized. ► Site-specific and highly stable labeling with the {99mTc(CO)3}+ moiety was achieved. ► Full characterization was performed on the corresponding cold {Re(CO)3}+ conjugates. ► The 99mTc-porphyrin conjugates combine radio and optical imaging modalities. ► We describe here the first, thoroughly characterized, 99mTc-porphyrin conjugates.