Zn Complex of Diaminedithiol Tetradentate Ligand as a Stable Precursor for (99m)Tc-Labeled Compounds

The diaminedithiol (N(2)S(2)) tetradentate ligand constitutes a useful chelating molecule for preparing (99m)Tc-labeled compounds of high in vivo stability in high radiochemical yields. However, since the thiol groups in the N(2)S(2) ligand are easy to be oxidized to disulfide bonds, they need to be protected with an appropriate protecting group, which hinders the broad applications of the N(2)S(2) ligand for radiopharmaceuticals. In this study, a Zn chelate of N(2)S(2) was evaluated as a precursor for purification-free (99m)Tc-labeled N(2)S(2) under the mild and simple procedure. Zn-N(2)S(2) was prepared by reacting Zn acetate with N(2)S(2), and the Zn-N(2)S(2) remained stable under aerobic conditions at room temperature. (99m)Tc-N(2)S(2) was obtained over 90% radiochemical yields at room temperature by a one-pot reaction, consisting of Zn-N(2)S(2) (10(−5) M), (99m)TcO(4)(−), ethylenediaminetetraacetic acid (EDTA), and a reducing agent (Sn(2+)) at pH = 5.5 to 7.5. (99m)Tc-N(2)S(2) was also obtained over 90% radiochemical yields when the reaction was conducted in the presence of an equimolar amount of IgG antibody. These findings indicate the Zn complex of N(2)S(2) ligand constitutes a stable and useful precursor to prepare (99m)Tc-labeled N(2)S(2) compounds in high yields under the mild and simple procedure.