A new bifunctional tridentate NSN ligand leading to cationic tricarbonyl fac- M(NSN)(CO)(3) (+) (M = Re, Tc-99m) complexes

Abstract

The synthesis and characterization of the new NSN tridentate bifunctional chelating agent 3-[2-(2'-pyridin-2-yl-ethylsulfanyl)ethylamino] propionic acid (as its hydrochloric salt, 1) and of its corresponding rhenium comp lex fac-[Re(NSN)(CO)(3)](+), 2, is described. Both compounds were characterized by elemental analysis, IR and NMR spectroscopies and X-ray crystallography. In complex 2 the coordination geometry around rhenium is distorted octahedral with the NSN atoms participating in the coordination sphere while the carboxylate group remains free. At tracer level, the analogous complex fac-[Tc-99m(NSN)(CO)(3)](+), 3, was obtained in high yield by reacting ligand 1 with the fac-[Tc-99m(H2O)(3)(CO)(3)](+) precursor at pH 6.5. The structure of 3 was established by HPLC comparison to the prototype rhenium comp lex 2. Complex 3 is stable in solution as well as in the presence of strongly coordinating agents like histidine or cysteine. Our data indicate that ligand 1 can be used as a bifunctional NSN chelating agent in the design of potential Tc-99m-radiopharmaceuticals. (C) 2013 Elsevier B.V. All rights reserved.