99mTc(I) Scorpionate Complexes for Brain Imaging: Synthesis, Characterization and Biological Evaluation

Carolina      Moura; Lurdes      Gano; Isabel      C. Santos; Antonio      Paulo; Isabel      Santos

Abstract

The new dihydrobis(azolyl)borate ligand Na[H2B(timMe)(3,5-Me2pz)] (L1) was synthesized and used to prepare the complexes fac-[M(κ3-H(μ-H)B(timMe)(3,5-Me2-pz))(CO)3] (M = Re (4), 99mTc (4a)). L1 and 4 were characterized by common analytical techniques, including X-ray diffraction analysis for 4. The successful synthesis of complex 4a, obtained with high radiochemical purity, has shown for the first time that dihydrobis(azolyl)borate ligands combining 2- mercaptoimidazolyl and pyrazolyl rings are capable of stabilizing the fac-[99mTc(CO)3]+ unit. Complex 4a displays a high in vitro stability, in PBS (pH 7.4), indicating that the B-H … 99mTc bond is retained even under physiological conditions. Biodistribution studies in mice have shown that 4a can cross the blood – brain barrier, emerging as a good alternative for the design of radiopharmaceuticals for brain imaging.

Keywords: Technetium-99m, brain imaging, poly(azolyl)borates, tricarbonyl, Diffraction

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