Synthesis, Nicotinic Acetylcholine Receptor Binding, and Antinociceptive Properties of 2- exo -2-(2‘-Substituted 5‘-pyridinyl)-7-azabicyclo[2.2.1]heptanes. Epibatidine Analogues
ABSTRACT A convenient, high-yield synthesis of 7-tert-butoxycarbonyl-7-azabicyclo[2.2.1]hept-2-ene (5), which involved the addition of tributyltin hydride to 7-tert-butoxycarbonyl-2-p-toluenesulfonyl-7-azabicyclo[2.2.1]hept-2-ene (4) followed by elimination of the tributyltin and p-tolylsulfonyl groups using tetrabutylammonium fluoride was developed. The addition of 2-amino-5-iodopyridine to 5 under reductive Heck conditions provided 7-tert-butoxycarbonyl-2-exo-(2'-amino-5'-pyridinyl)-7-azabicyclo[2.2.1]heptane (6). Compound 6 was the key intermediate used to prepare epibatidine analogues where the 2'-chloro group on the pyridine ring was replaced with a fluorine (1b), bromine (1c), iodine (1d), hydroxy (1e), amino (1f), dimethylamino (1g), trifluoromethanesulfonate (1h), and hydrogen (1i) group. (+)- and (-)-Epibatidine and compounds 1b-d and 1i all possess similar binding affinities at the alpha(4)beta(2) nAChR receptors labeled by [(3)H]epibatidine. Compound 1f has affinity similar to nicotine, whereas compounds 1e, 1g, and 1h have much lower affinity. The binding affinity appears to be dependent upon the electronic nature of the substituent. However, other factors are also involved. None of the compounds possesses appreciable affinity for the alpha(7) nAChR labeled by [(125)I]iodo-MLA. With the exception of 1f and 1g, all the epibatidine analogues are full agonists (tail flick test) in producing antinociception after intrathecal injection in mice.
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- "Nevertheless, the binding and agonistic potential of epibatidine (1) had tremendous stimulating impact on the nACh receptors research. A number of ligands with high in vitro affinity for the α4β2 subtype have been radiolabeled, and tested for in vivo imaging of the brain nAChRs       . Remarkable high affinities to the nAChRs have been registered in simple azetidinyl-pyridyl and pyrrolidinyl-pyridyl ethers (A-85380 and A-84543, Fig. 1) . "
ABSTRACT: Neuronal nicotinic acetylcholine receptors (nAChRs) are transmembrane ligand-gated ion channels. Recent research demonstrated that selective nAChR ligands may have therapeutic potential in a number of CNS diseases and disorders. The alkaloid epibatidine is a highly potent non-opioid analgesic and nAChR agonist, but too toxic to be a useful ligand. To develop ligands selective for distinct nAChR subtypes and with reduced toxicity, a series of epibatidine and homoepibatidine analogues were synthesized. (+/-)-8-Methyl-3-(pyridin-3-yl)-8-azabicyclo[3,2,1]oct-2-ene, showed high affinity towards alpha4beta2 (Ki=2 nM), subtype selectivity (alpha4beta2/alpha7 affinity ratio>100) and relatively low toxicity in mice and can be labeled with 11C and 18F as positron emission tomography (PET) tracers for imaging of nAChRs.European Journal of Medicinal Chemistry 05/2006; 41(5):640-50. DOI:10.1016/j.ejmech.2006.01.015 · 3.45 Impact Factor
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ABSTRACT: A series of 2'-substituted-3'-phenyl epibatidine analogues were synthesized and evaluated for inhibition of binding at nicotine acetylcholine receptors and for antinociceptive properties in mice. The introduction of a bulky phenyl group at the 3'-position exerted a profound influence on both receptor binding and antinociceptive effects. Substitution of different groups at the 2'-position distinguished between agonist and antagonist properties. These results demonstrate that structural requirements for receptor activities and recognition are distinctively different.Journal of Medicinal Chemistry 12/2001; 44(24):4039-41. DOI:10.1021/jm015561v · 5.45 Impact Factor
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ABSTRACT: Syntheses of (+/-)-homoepibatidine analogues (2), which contain the 8-azabicyclo [3.2.1]octane ring system, were achieved by using palladium-catalyzed reductive-coupling reaction from 3 and the analgesic activity was tested by Mouse writhing antinociceptive assay.Archives of Pharmacal Research 03/2002; 25(1):49-52. DOI:10.1007/BF02975260 · 2.05 Impact Factor