INVESTIGATION OF THE LABELING CHARACTERISTICS OF TC-99M-MERCAPTOACETYLTRIGLYCINE

S-Benzyl-, S-benzamidomethyl- and S-benzoylmercaptoacetyltriglycine were synthesized and compared in exchange labelling experiments for the preparation of Tc-99m-MAG3. The rate of exchange from Tc-99m-tartrate to Tc-99m-MAG3 starting from the respective precursors was determined in different conditions. Labelling proceeded most rapidly starting from the S-benzoyl protected precursor but efficient labelling was also accomplished using the more stable S-benzamidomethyl- and S-benzylmercaptoacetyltriglycine. Tc-99m-MAG3 was also prepared by direct labelling of unprotected mercaptoacetyltriglycine at alkaline pH. Radiochemical purity in these conditions is mainly dependent on the pH during labelling.