Insight into Technetium Amidoxime Complex: Oxo Technetium(V) Complex of N-Substituted Benzamidoxime as New Basic Structure for Molecular Imaging

In search of benzamidoxime (BHam) derivatives that provide a single 99mTc-labeled compound of high in vivo stability, we synthesized three N-alkyl compounds of benzamidoxime (BHam) ligand. They provided a single 99mTc-labeled compound by ligand exchange reaction of 99mTc-glucoheptonate in high radiochemical yields (over 95% at MBHam concentration of 1 × 10−5 M). 99mTc-N-methyl benzamidoxime (99mTc-MBHam) showed higher stability than the parental 99mTc-BHam. The complex of this compound with 99gTcO3+ ion was prepared, isolated, and characterized by FT-IR and NMR spectra as well as X-ray diffraction. 99gTc-MBHam crystallized in an orthorhombic space group Pna21 with a = 13.4823(5), b = 15.5410(7), c = 7.7907(3) Å, V = 1632.39(11) Å3, and Z = 4. The 99gTc complex possessed square base pyramid coordination geometry. The equatorial plane was formed by two-amine nitrogen and two-oxime oxygen atoms in trans position, while the oxo core of the technetium(V) occupied the apical position. The 99gTc-MBHam proved to be identical with the 99mTc-MBHam prepared at the no-carrier-added level by comparison of their HPLC profiles.