Hydroxamamide as a chelating moiety for the preparation of 99mTc-radiopharmaceuticals III. Characterization of various 99mTc-hydroxamamides

Five hydroxamamide (Ham) derivatives with various nonpolar substituents and different lipophilicities have been selected as ligands for preparation of 99mTc-complexes. Analysis via high performance liquid chromatography (HPLC) resolved the 99mTc-complexes of each ligand into two radioactive components, which are considered as isomers. The stability of both components was studied at pH 5 and 7, showing good stability at pH 7, but some transition between the components at pH 5. Use of a mixture of two ligands for complexation showed not only the complexes of the separate ligands, but also complexes containing both ligands. These results indicate that hydroxamamides very likely form complexes composed of Ham and 99mTc in a 2:1 molar ratio. This may also explain the stability of the 99mTc-Ham complexes in spite of the bidentate character of a Ham ligand.