Preparation of a bromine-76 labelled analogue of epibatidine: a potent ligand for nicotinic acetylcholine receptor studies

Epibatidine analogues have been labelled with I-123 for single photon emission computed tomography and with short half-life positron emitters (C-11 and F-18) for PET. For easier radiopharmacological studies the bromo analogue of epibatidine (norchlorobromoepibatidine or exo-7-azabicyclo-2-(2-bromo-5-pyridyl)-[2.2.1]heptane) was labelled with Br-76, a longer half-life positron emitter, (T1/2=16.2 h). [76Br]-norchlorobromoepibatidine was prepared by using a Cu+ assisted bromodeiodination exchange from the iodo analogue in reducing conditions at 190°C. The tracer purified by RP-HPLC was obtained in 70% radiochemical yield with a specific radioactivity of 20 GBq/μmol. Radiochemical and chemical purities measured by radio-TLC and HPLC were >98%.