New Analogues of Epiboxidine Incorporating the 4,5-Dihydroisoxazole Nucleus: Synthesis, Binding Affinity at Neuronal Nicotinic Acetylcholine Receptors, and Molecular Modeling Investigations

Review of the synthesis of acyclic and cyclic oxime ethers

Oxime ethers have attracted much attention due to their potential biological activities and wide variety of synthetic applications.

Ligand-controlled stereodivergent 1,3-dipolar cycloaddition of azomethine ylides with 3-methyl-4-nitro-5-styrylisoxazoles

An unprecedented Ag(i)-catalyzed ligand-controlled stereodivergent 1,3-dipolar cycloaddition of azomethine ylides with 3-methyl-4-nitro-5-styrylisoxazoles has been developed to afford heterocycles bearing both methylisoxazole and pyrrolidine moieties.

1,3-Dipolar cycloadditions of nitrile oxides with 7-oxa- and 7-azabenzonorbornadienes

Dipolar cycloaddition reactions allow for the efficient construction of five-membered heterocycles, often with diverse medicinal applications. We examined the 1,3-dipolar cycloaddition of 7-oxabenzonorbornadienes and 7-azabenzonorbornadienes with acetonitrile oxide and benzonitrile oxide, achieving an assortment of heterobicycle-fused isoxazolines with good to excellent yields. All isoxazolines were consistently directed to the exo face of the bicyclic framework with complete stereoselectivity. Preliminary biological testing of the adducts also showed positive anti-cancer activity, suggesting their potential pharmaceutical utility.

The enantiomers of epiboxidine and of two related analogs: synthesis and estimation of their binding affinity at α4β2 and α7 neuronal nicotinic acetylcholine receptors

Epiboxidine hydrochlorides (+)-2 and (-)-2, which are the structural analogs of the antipodes of epibatidine (±)-1, as well as the enantiomeric pairs (+)-3/(-)-3 and (+)-4/(-)-4 were synthesized and tested for binding affinity at α4β2 and α7 nicotinic acetylcholine receptor (nAChR) subtypes. Final derivatives were prepared through the condensation of racemic N-Boc-7-azabicyclo[2.2.1]heptane-2-one (±)-5 with the resolving agent (R)-(+)-2-methyl-2-propanesulfinamide. The pharmacological analysis carried out on the three new enantiomeric pairs evidenced an overall negligible degree of enantioselectivity at both nAChRs subtypes, a result similar to that reported for both natural and unnatural epibatidine enantiomers at the same investigated receptor subtypes.

Design, synthesis, and pharmacological characterization of novel spirocyclic quinuclidinyl-Δ2-isoxazoline derivatives as potent and selective agonists of α7 nicotinic acetylcholine receptors

A set of racemic spirocyclic quinuclidinyl-Δ(2)-isoxazoline derivatives was synthesized using a 1,3-dipolar cycloaddition-based approach. Target compounds were assayed for binding affinity toward rat neuronal homomeric (α7) and heteromeric (α4β2) nicotinic acetylcholine receptors. Δ(2) -Isoxazolines 3 a (3-Br), 6 a (3-OMe), 5 a (3-Ph), 8 a (3-OnPr), and 4 a (3-Me) were the ligands with the highest affinity for the α7 subtype (K(i) values equal to 13.5, 14.2, 25.0, 71.6, and 96.2 nM, respectively), and showed excellent α7 versus α4β2 subtype selectivity. These compounds, tested in electrophysiological experiments against human α7 and α4β2 receptors stably expressed in cell lines, behaved as partial α7 agonists with varying levels of potency. The two enantiomers of (±)-3-methoxy-1-oxa-2,7-diaza-7,10-ethanospiro[4.5]dec-2-ene sesquifumarate 6 a were prepared using (+)-dibenzoyl-L- or (-)-dibenzoyl-D-tartaric acid as resolving agents. Enantiomer (R)-(-)-6 a was found to be the eutomer, with K(i) values of 4.6 and 48.7 nM against rat and human α7 receptors, respectively.