Synthesis of a radioiodinated analog of epibatidine: (±)-exo-2-(2-iodo-5-pyridyl)-7-azabicyclo [2.2.1]heptane for in vitro and in vivo studies of nicotinic acetylcholine receptors

[¹²⁵I] or [¹²³I] labeled (±)-exo-2-(2-iodo-5-pyridyl)-7-azabicyclo[2.2.1]heptane (IPH), an analog of the high-affinity nicotinic acetylcholine receptor ligand, epibatidine, was prepared by a nucleophilic non-isotopic exchange reaction. Treatment of the 2-bromo pyridyl precursor with radioiodide and in situ generated Cu(I) at high temperature (200-220°C) gave [¹²⁵I] or [¹²³I]IPH that was purified by reverse phase HPLC. Radiochemical yields ranged from 31-50% for the [¹²⁵I] labeling (average = 37%, n = 7) and 20% for [¹²³I]. Both [¹²⁵I]IPH and [¹²³I]IPH were of high radiochemical purity (> 96%) and high specific activity (average of 1540 mCi/μmol (57 GBq/μmol) for [¹²⁵I]IPH and >1750 mCi/μmol (65 GBq/μmol) for [¹²³I]IPH).