Preparation of high specific activity [15,16-3H]-7-benzylidenenaltrexone

The preparation of the δ 1 -specific ligand 7-benzylidenenaltrexone (BNTX), labeled with tritium at high specific activity (14.4 Ci/mmol) was prepared in 33% yield and >98% purity by the aldol condensation of high specific activity [15,16- 3 H]naltrexone with benzaldehyde at high dilution.