Labeling of polyaminomacrocyclic ligands BY99mTcO 4 − reduction and exchange reactions

The cationic^99mTc-complexes of 1,4,8,12-tetraazacyclopentadecane (15-ane-N₄), 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (Me₄cyclam) and 1,4,7,10,13,16-hexaazacyclooctadecane (hexacyclen) are obtained in yields higher than 80% by^99mTcO ₄ ^– reduction at pH 12. The electrophoretic and chromatographic analyses show that these ligands form structurally similar complexes. Efficient labeling of 15-ane-N₄ (>95%) is obtained by the exchange reaction with^99mTc-citrate,^99mTc-ENDA and^99mTc-HBA at pH 12. The labeling yield of hexacyclene is 70% and 85% following the reaction with^99mTc-ENDA and^99mTc-HBA and^99mTc-citrate, respectively. The labeling of Me₄cyclam is very poor (about 10%) except starting from^99mTc-citrate (55%). The results are compared wint the available data for well characterized TcO₂L]⁺ complexes.