Synthesis of [3H]naltrindole [1]

[H-3]Naltrindole ([H-3] 1) was prepared for use as a selective radiolabeled ligand for delta opioid receptors. The Fischer indole synthesis from naltrexone and 2,4-dibromophenylhydrazine produced dibromide precursor 2, which was catalytically dehalogenated with carrier free tritium gas to afford [H-3] 1 in 45.8% yield at a specific activity of 39.5 Ci/mmol.