Neutral oxorhenium(V) and oxotechnetium(V) complexes with novel amide thioether dithiolate ligands derived from cysteine

Summary. Bifunctional ligands able to form neutral complexes with radioactive technetium and rhenium and to couple to biological relevant anchor groups play an important role in the design of new radiopharmaceuticals for diagnosis and therapy. A novel tetradentate amide thioether dithiolate ligand HS-CH₂CH₂-S-CH₂CONH-CH(COOR)CH₂SH(H₃SNSS) with R = CH₃, C₁₀H₂₁ was synthesized that forms stable complexes with technetium and rhenium in oxidation state V. The molecular structures of the rhenium and technetium complexes MO(SNSS) were determined by X-ray structural analysis and show that the metal coordination number is five and the coordination polyhedron is between square-pyramidal and trigonal-bipyramidal. The pendent ester group allows coupling of the chelate unit at biologically relevant anchor groups. As a relevant representative the X-ray structural analysis of the rhenium decylester complex was carried out. The complex formation with Tc at teh n.c.a. level and ¹⁸⁶Re at 10^-10M level is described.