Structure–activity studies of a novel series of isoxazole-3-carboxamide derivatives as TRPV1 antagonists

Insights from molecular dynamics simulations of TRPV1 channel modulators in pain

TRPV1 is a nonselective cation channel vital for detecting noxious stimuli (heat, acid, capsaicin). Its role in pain makes it a potential drug target for chronic pain management, migraines, and related disorders. This review updates molecular dynamics (MD) simulation studies on the TRPV1 channel, focusing on its gating mechanism, ligand-binding sites, and implications for drug design. The article also explores challenges in developing modulators, SAR optimization, and clinical trial studies. Efforts have been undertaken to concisely present MD simulation findings, with a focus on their relevance to drug discovery.

The synthetic and therapeutic expedition of isoxazole and its analogs

Isoxazole, constituting an important family of five-membered heterocycles with one oxygen atom and one nitrogen atom at adjacent positions is of immense importance because of its wide spectrum of biological activities and therapeutic potential. It is, therefore, of prime importance that the development of new synthetic strategies and designing of new isoxazole derivatives should be based on the most recent knowledge emerging from the latest research. This review is an endeavor to highlight the progress in the chemistry and biological activity of isoxazole derivatives which could provide a low-height flying bird's eye view of isoxazole derivatives to the medicinal chemists for the development of clinically viable drugs using this information.

Medicinal Chemistry, Pharmacology, and Clinical Implications of TRPV1 Receptor Antagonists

Transient receptor potential vanilloid 1 (TRPV1) is an ion channel expressed on sensory neurons triggering an influx of cations. TRPV1 receptors function as homotetramers responsive to heat, proinflammatory substances, lipoxygenase products, resiniferatoxin, endocannabinoids, protons, and peptide toxins. Its phosphorylation increases sensitivity to both chemical and thermal stimuli, while desensitization involves a calcium-dependent mechanism resulting in receptor dephosphorylation. TRPV1 functions as a sensor of noxious stimuli and may represent a target to avoid pain and injury. TRPV1 activation has been associated to chronic inflammatory pain and peripheral neuropathy. Its expression is also detected in nonneuronal areas such as bladder, lungs, and cochlea where TRPV1 activation is responsible for pathology development of cystitis, asthma, and hearing loss. This review offers a comprehensive overview about TRPV1 receptor in the pathophysiology of chronic pain, epilepsy, cough, bladder disorders, diabetes, obesity, and hearing loss, highlighting how drug development targeting this channel could have a clinical therapeutic potential. Furthermore, it summarizes the advances of medicinal chemistry research leading to the identification of highly selective TRPV1 antagonists and their analysis of structure-activity relationships (SARs) focusing on new strategies to target this channel.

Isomerizable (E/Z)-alkynyl-O-methyl oximes employing TMSCl–NCS in chlorinative cyclization for the direct synthesis of 4-chloroisoxazoles

For the first time, 4-chloroisoxazoles are directly synthesized in moderate to excellent yields from mixtures of (E)- and (Z)-alkynyl-O-methyl oximes via (E)- to (Z)-oxime isomerization followed by chlorinative cyclization.

Synthesis of 3,4,5-Trisubstituted Isoxazoles from Morita-Baylis-Hillman Acetates by an NaNO2 /I2 -Mediated Domino Reaction

An efficient NaNO2 /I2 -mediated one-pot transformation of Morita-Baylis-Hillman (MBH) acetates into alkyl 3-nitro-5-(aryl/alkyl)isoxazole-4-carboxylates is described. In a cascade event, initial Michael addition of NaNO2 to the MBH acetate furnishes the allylnitro intermediate which undergoes I2 -catalyzed oxidative α-CH nitration of the nitromethyl subunit followed by [3+2] cycloaddition to afford the title compounds. Structural elaborations of these highly substituted isoxazoles by SN Ar reactions and hydrogenolysis allows access to useful products.

Ruthenium-catalyzed cycloadditions of 1-haloalkynes with nitrile oxides and organic azides: synthesis of 4-haloisoxazoles and 5-halotriazoles

(Cyclopentadienyl)(cyclooctadiene) ruthenium(II) chloride [CpRuCl(cod)] catalyzes the reaction between nitrile oxides and electronically deficient 1-choro-, 1-bromo-, and 1-iodoalkynes leading to 4-haloisoxazoles. Organic azides are also suitable 1,3-dipoles, resulting in 5-halo-1,2,3-triazoles. These air-tolerant reactions can be performed at room temperature with 1.25 equivalents of the respective 1,3-dipole relative to the alkyne component. Reactive 1-haloalkynes include propiolic amides, esters, ketones, and phosphonates. Post-functionalization of the halogenated azole products can be accomplished by using palladium-catalyzed cross-coupling reactions and by manipulation of reactive amide groups. The lack of catalysis observed with [Cp*RuCl(cod)] (Cp* = pentamethylcyclopentadienyl) is attributed to steric demands of the Cp* (η(5)-C5Me5) ligand in comparison to the parent Cp (η(5)-C5H5). This hypothesis is supported by the poor reactivity of [(η(5)-C5Me4CF3)RuCl(cod)], which serves as a an isosteric mimic of Cp* and as an isoelectronic analogue of Cp.

Direct synthesis of 4-fluoroisoxazoles through gold-catalyzed cascade cyclization-fluorination of 2-alkynone O-methyl oximes

A tandem protocol for the synthesis of fluorinated isoxazoles has been developed via catalytic intramolecular cyclizations of 2-alkynone O-methyl oximes and ensuing fluorination. The reactions proceed smoothly at room temperature in the presence of 5 mol % of (IPr)AuCl, 5 mol % of AgOTs, 2.5 equiv of Selectfluor, and 2 equiv of NaHCO3. This process features an efficient one-pot cascade route to fluoroisoxazoles with high yields and high selectivity under mild reaction conditions.

Design and synthesis of conformationally restricted capsaicin analogues based in the 1, 3, 4-thiadiazole heterocycle reveal a novel family of transient receptor potential vanilloid 1 (TRPV1) antagonists

4-hydroxy-3-methoxybenzaldehyde was used as starting material to obtain a number of 1, 3, 4-thiadiazole alkylamide derivatives. The pharmacological properties of these conformationally restricted capsaicin analogues were evaluated on HEK-293T cells transiently expressing TRPV1 receptor. By means of a highthroughput calcium imaging assay we find that 1, 3, 4-thiadiazoles (compounds 8-15) act as potent antagonists of the capsaicin receptor, inhibiting both, the capsaicin- and temperature-dependent activation. Docking studies suggested a different binding orientation on the vanilloid binding site when compared with capsaicin analogues, such as 5-iodononivamide. Overall, our studies suggest that 1, 3, 4-thiadiazoles interact with capsaicin's binding region of the receptor, although using a different set of interactions within the vanilloid binding pocket.

Discovery of potent, soluble and orally active TRPV1 antagonists. Structure-activity relationships of a series of isoxazoles

Systematic optimisation of a poorly soluble lead series of isoxazole-3-carboxamides was conducted. Substitution of the 4-position with specific polar functionality afforded the requisite balance of potency, solubility and physicochemical properties. Compound 21a was found to be efficacious in the rat Capsaicin Hargreaves assay following oral administration.