Synthesis and Nicotinic Acetylcholine Receptor Binding Properties of exo-2-(2‘-Fluoro-5‘-pyridinyl)-7-azabicyclo- [2.2.1]heptane:  A New Positron Emission Tomography Ligand for Nicotinic Receptors

Journal of Medicinal Chemistry
1997.0

Abstract

Epibatidine (1a), a unique alkaloid isolated from the skin of the Ecuadoran poison frog Epipedobates tricolor, is a potent analgesic agent whose effects are mediated via neuronal nicotinic acetylcholine receptors (nAChRs). Previous studies on (+)- and (-)-[3H]norchloroepibatidine ([3H]NCEPB, 1c) showed higher levels of specific in vivo binding to nAChRs compared to 1a, suggesting that exo-2-(2′-fluoro-5′-pyridinyl)-7-azabicyclo[2.2.1]heptane (1b, norchlorofluoroepibatidine, NFEP) might have favorable binding properties and its 18F analog could serve as a positron emission tomography (PET) ligand for nAChR characterization. In this report, we developed an efficient synthesis of 1b (adaptable for 1a synthesis) by modifying Clayton and Regan's route, using an N-tert-butyloxycarbonyl protecting group for mild deprotection: (p-tolylsulfonyl)acetylene (5) reacted with N-(tert-butoxycarbonyl)pyrrole (6) to give diene 7, which was reduced to olefin 8; desulfonation of 8 yielded 7-(tert-butoxycarbonyl)-7-azabicyclo[2.2.1]hept-2-ene (9), which coupled with 2-amino-5-iodopyridine (4b) to form 10; diazotization of 10 in pyridine/HF afforded 1b. We also synthesized 7-(tert-butyloxycarbonyl)-2-exo-[2′-(N,N,N-trimethylammoniumyl)-5′-pyridinyl]-7-azabicyclo[2.2.1]heptane iodide (2) as a more efficient precursor for [18F]-1b (70% radiochemical yield) than previous analogs. Competition binding experiments showed 1b had a Kapp value of 0.020 nM, over 300 times more potent than nicotine (6.2 nM). [18F]-1b demonstrated high brain uptake (12-15% in baboons), high in vivo specificity for nAChRs, and a high thalamus-to-cerebellum ratio (4.0-4.5 in baboons at 2 h), providing a high signal-to-noise ratio for PET imaging. In summary, we developed efficient syntheses of 1b and 1a, and 2 is an excellent precursor for [18F]-1b, which offers a new PET tool for studying nAChRs in neurodegeneration and addiction.

Knowledge Graph

Similar Paper

Synthesis and Nicotinic Acetylcholine Receptor Binding Properties of exo-2-(2‘-Fluoro-5‘-pyridinyl)-7-azabicyclo- [2.2.1]heptane:  A New Positron Emission Tomography Ligand for Nicotinic Receptors
Journal of Medicinal Chemistry 1997.0
Synthesis, Nicotinic Acetylcholine Receptor Binding, and Antinociceptive Properties of 2-exo-2-(2‘-Substituted 5‘-pyridinyl)-7-azabicyclo[2.2.1]heptanes. Epibatidine Analogues
Journal of Medicinal Chemistry 2001.0
Synthesis and Evaluation of N-[<sup>11</sup>C]Methylated Analogues of Epibatidine as Tracers for Positron Emission Tomographic Studies of Nicotinic Acetylcholine Receptors
Journal of Medicinal Chemistry 1998.0
New synthesis and evaluation of enantiomers of 7-methyl-2-exo-(3′-iodo-5′-pyridinyl)-7-azabicyclo[2.2.1]heptane as stereoselective ligands for PET imaging of nicotinic acetylcholine receptors
Bioorganic &amp; Medicinal Chemistry Letters 2008.0
Synthesis and Biological Evaluation at Nicotinic Acetylcholine Receptors of N-Arylalkyl- and N-Aryl-7-Azabicyclo[2.2.1]heptanes
Journal of Medicinal Chemistry 2002.0
Derivatives of (−)-7-Methyl-2-(5-(pyridinyl)pyridin-3-yl)-7-azabicyclo[2.2.1]heptane Are Potential Ligands for Positron Emission Tomography Imaging of Extrathalamic Nicotinic Acetylcholine Receptors
Journal of Medicinal Chemistry 2007.0
Synthesis and binding affinity at α4β2 and α7 nicotinic acetylcholine receptors of new analogs of epibatidine and epiboxidine containing the 7-azabicyclo[2.2.1]hept-2-ene ring system
Bioorganic &amp; Medicinal Chemistry Letters 2012.0
Synthesis, Nicotinic Acetylcholine Receptor Binding, and Antinociceptive Properties of 2-exo-2-(2‘,3‘-Disubstituted 5‘-pyridinyl)-7-azabicyclo[2.2.1]heptanes:  Epibatidine Analogues
Journal of Medicinal Chemistry 2002.0
exo-2-(Pyridazin-4-yl)-7-azabicyclo[2.2.1]heptanes:  Syntheses and Nicotinic Acetylcholine Receptor Agonist Activity of Potent Pyridazine Analogues of (±)-Epibatidine
Journal of Medicinal Chemistry 2001.0
Synthesis, Nicotinic Acetylcholine Receptor Binding, and Antinociceptive Properties of 2′-Fluoro-3′-(substituted pyridinyl)-7-deschloroepibatidine Analogues
Journal of Medicinal Chemistry 2014.0