Synthesis, Nicotinic Acetylcholine Binding, and in Vitro and in Vivo Pharmacological Properties of 2 '-Fluoro-(carbamoylpyridinyl)deschloroepibatidine Analogues
In this study, we report the synthesis, nAChR in vitro and in vivo pharmacological properties of 2'-fluoro(carbamoylpyridinyl)deschloroepibatidine analogues (5, 6a,b, and 7a,b), which are analogues of our lead structure epibatidine. All of the analogues had subnanomolar binding affinity for alpha 4 beta 2*-nAChRs, and all were potent antagonists of alpha 4 beta 2-nAChRs in an in vitro functional assay. Analogues 6a,b were also highly selective for alpha 4 beta 2- relative to alpha 3 beta 4- and alpha 7-nAChRs. Surprisingly, all of the analogues were exceptionally potent antagonists of nicotine -induced antinociception in the mouse tail -flick test, relative to standard nAChR antagonists such as DH beta E. 2'-Fluoro-(4-carbamoyl-3-pyridinyl)deschloroepitabidine (6a) displayed an attractive combination of properties, including subnanomolar binding affinity (K-i = 0.07 nM), submicromolar inhibition of alpha 4 beta 2-nAChRs in the functional assay (IC50 = 0.46 mu M) with a high degree of selectivity for alpha 4 beta 2-relative to the alpha 3 beta 4/alpha 7-nAChRs (54-/348-fold, respectively), potent inhibition of [H-3]dopamine release mediated by alpha 4 beta 2*-and alpha 6 beta 2*-nAChRs in a synaptosomal preparation (IC50 = 21 and 32 nM, respectively), and an AD(50) of 0.007 mu g/kg as an antagonist of nicotine induced antinociception in the mouse tail -flick test which is 64 250 times more potent than DH beta E. These data suggest that compound 6a will be highly useful as a pharmacological tool for studying nAChRs and merits further development.