Preparation of No-Carrier-Added Technetium-99m Complexes via Metal-Assisted Cleavage from a Solid Phase

A novel method for the preparation of no-carrier-added (nca) complexes [99mTc(CO)3L] (L = diethylenetriamine or picolylamine-N-acetic acid) is described. The ligands were covalently bound to a solid support of organic polymers via formation of a tertiary amine from the chelating unit. This C−N bond to the solid phase is selectively cleaved during the formation of the technetium complexes by intramolecular nucleophilic attack of a remaining hydroxy ligand to the α-carbon. The complex [99mTc(CO)3L] is released into solution while uncomplexed ligand and uncleaved complex remain solid-phase bound. High specific activity technetium complexes can then be isolated by simple filtration. Cleavage yield depends on temperature, pH, and ligand. Up to 50% release from the solid phase could be achieved under optimized conditions. Corresponding to the 99mTc concentration, free ligand is present in concentrations lower than 10-7 M. If a targeting vector is conjugated to these ligands, no-carrier-added radiopharmaceuticals can be prepared in that way.