Synthesis, Nicotinic Acetylcholine Receptor Binding, and in Vitro and in Vivo Pharmacological Properties of 2 '-Fluoro-(substituted thiophenyl)deschloroepibatidine Analogues
The synthesis, nAChR in vitro and in vivo pharmacological properties of 2'-fluoro-3'-(substituted thiophenyl)deschloroepibatidine analogues (5a-f, 6a-d, and 7a-c) are presented herein. All had subnanomolar affinity at alpha 4 beta 2*-nAChRs. Contrary to lead structure epibatidine, a potent nAChR agonist, all were potent alpha 4 beta 2- and alpha 3 beta 4-AChR antagonists in an in vitro functional assay. In vivo, the compounds were also nAChR antagonists, with various degrees of agonist activity. Compounds 5e, 5f, 6a, 6c, 6d, and 7c had no agonist effects in the tail-flick, hot-plate, hypothermia, or spontaneous activity tests, Whereas 5a-d, 7a and 7b did not have agonist activity in the tail-flick and hotplate tests but, like varenicline, were agonists in the hypothermia and spontaneous activity tests. Compound 6b had agonist activity in all four in vivo tests. All the compounds were antagonists of nicotine-induced antinociception in, the tail-flick test, and all except 5c, 5d; 5f, and 6b were antagonists of nicotine-induced antinociception in the hotplate test. Compound 7c, which had a K-i = 0.86 nM in the binding assay similar potency at alpha 4 beta 2/alpha 3 beta 4 with selectivity relative to alpha 7 nAChRs, had an AD(50) value of 0.001 mu g/kg in the tail-flick test with no agonist activity in the in vitro or in vivo test had one of the more interesting profiles.