Thiosemicarbazonate complexes with affinity for amyloid-β fibers: synthesis, characterization and biological studies

Aim: Obtain radioimages of amyloid-β fibers using ^99mTc-complexes. Methodology: Tridentate thiosemicarbazone and thiocarbonohydrazone ligands containing fragments (stilbene, azobenzene, benzothiazole or benzoxazole) with affinity for amyloid-ß fibers and its Re(I) complexes have been prepared. The molecular structures of several ligands and complexes were determined by x-ray diffraction. Binding affinity studies toward Aß_1-42 fibers were performed for the ligands and Re(I) complexes. The ability of formation of some ^99mTc(I) complexes, their biodistribution and in vivo stability have been established. Results & conclusion: Complexes of stilbene and benzothiazole thiosemicarbazonates show similar affinity for amyloid-β fibers to the free ligand. These ^99mTc complexes present a reasonable in vivo stability and a low capability to cross the blood-brain barrier although not sufficient to brain amyloid imaging.