Synthesis of Selective Agonists for the α7 Nicotinic Acetylcholine Receptor with In Situ Click-Chemistry on Acetylcholine-Binding Protein Templates

Abstract

The acetylcholine-binding proteins (AChBPs), which serve as structural surrogates for the extracellular domain of nicotinic acetylcholine receptors (nAChRs), were used as reaction templates for in situ click-chemistry reactions to generate a congeneric series of triazoles from azide and alkyne building blocks. The catalysis of in situ azide-alkyne cycloaddition reactions at a dynamic subunit interface facilitated the synthesis of potentially selective compounds for nAChRs. We investigated compound sets generated in situ with soluble AChBP templates through pharmacological characterization with ␣7 and ␣4␤2 nAChRs and 5-hydroxytryptamine type 3A receptors. Analysis of activity differences between the triazole 1,5-synand 1,4-anti-isomers showed a preference for the 1,4-antitriazole regioisomers among nAChRs. To improve nAChR subtype selectivity, the highest-potency building block for ␣7 nAChRs, i.e., 3␣-azido-N-methylammonium tropane, was used for additional in situ reactions with a mutated Aplysia californica AChBP that was made to resemble the ligand-binding domain of the ␣7 nAChR. Fourteen of 50 possible triazole products were identified, and their corresponding tertiary analogs were synthesized. Pharmacological assays revealed that the mutated binding protein template provided enhanced selectivity of ligands through in situ reactions. Discrete trends in pharmacological profiles were evident, with most compounds emerging as ␣7 nAChR agonists and ␣4␤2 nAChR antagonists. Triazoles bearing quaternary tropanes and aromatic groups were most potent for ␣7 nAChRs. Pharmacological characterization of the in situ reaction products established that click-chemistry synthesis with surrogate receptor templates offered novel extensions of fragment-based drug design that were applicable to multisubunit ion channels.

Biomolecular recognition of antagonists by α7 nicotinic acetylcholine receptor: Antagonistic mechanism and structure–activity relationships studies

“…Recently, there is immense attraction in measuring the functional and structural multiplicity of a7 nAChR, and in exploiting a7 nAChR selective agonists that have latent as curative ligands for diseases, e.g. brain fog, neurodegeneration, and other CNS pathologies (Yamauchi et al, 2012;Kombo and Bencherif, 2013;Rankovic, 2015). Regrettably, relatively little consideration has concentrated on the development of a7 nAChR antagonists as potential pharmaceutical candidates, even though a7 nAChR selective antagonists have been believed to be useful in the medication of neuropathology and complaint (Garcia-Delgado et al, 2010;Crestey et al, 2013;Islam, 2015).…”

Ruthenium-Catalyzed Azide Alkyne Cycloaddition Reaction: Scope, Mechanism, and Applications

“…A diverse set of 1,5-triazole products can be found in these reports which cover a wide range of targets and target classes including various enzyme inhibitors, [203][204][205][206][207][208][209][210][211][212][213] kinases, [214][215][216][217] proteases, 110,112 antivirals 218 (see also chapter 5.3) G-protein coupled receptors (GPCRs), 219 ion channels, [220][221][222] heat shock proteins, 95 and tRNA ligands. 223 1,5-Triazole derivatives have shown activity against numerous cancer cell lines, 205,215,[224][225][226][227] and against the parasites Trypanosoma cruzi 70,228 and Plasmodium falciparum.…”

Design and Synthesis of Nicotinic Acetylcholine Receptor Antagonists and their Effect on Cognitive Impairment

“…The binding affinity of the newly synthesized compounds was determined by radioligand competition assay against AChBPs from Lymnaea stagnalis ( Ls ), Aplysia californica ( Ac ), and Aplysia californica mutant ( Ac Y55W) . The screening test was performed to determine the fraction of [ 3 H]‐epibatidine binding with AChBPs.…”

“…Further functional assay for selectivity was performed using sensor cells expressing Ca 2+ ‐permeable LGIC receptors and a genetically encoded fluorescence resonance energy transfer (FRET)‐based calcium sensor (CNiFERs) . HEK cells expressing α 7‐nAChR, α 4 β 2 nAChR, and 5‐HT 3A receptors were analyzed by FRET response employing a fluorometric imaging plate reader system (FlexStation 3; Molecular Devices, Sunnyvale, CA, USA).…”