This study presents a novel regioselective synthesis of 3-electron-withdrawing-group-(EWG)-substituted 5-sulfonyl- and 5-sulfinylisoxazoles from 3-EWG-5-nitroisoxazoles via nucleophilic aromatic substitution with thiophenols followed by oxidation with m-chloroperbenzoic acid (mCPBA). The scope of the reactions was explored, demonstrating high yields across a variety of functional groups and substituents. Optimized conditions enabled selective oxidation of thioaryl groups to sulfonyl or sulfinyl derivatives. Biological evaluation revealed that several compounds, especially 3-nitro-5-sulfonyl- and 5-sulfinylisoxazoles, exhibit potent antimicrobial activity against Gram-positive bacteria, fungi, and notably low MICs comparable to those of standard drugs. The mechanism of action studies indicate that these compounds induce the bacterial SOS response without inhibiting DNA synthesis-related enzymes such as DNA polymerase I, DNA gyrase, or topoisomerases I and IV, suggesting activation via bacterial reductases. These findings highlight the potential of these isoxazole derivatives as promising antimicrobial agents and provide new insights into their mechanism of action.

The structures of isoxazole-containing cyclovinylogues of the intracellular fructose transporter protein GLUT5 inhibitor, N-(4-methylsulfonyl-2-nitrophenyl)benzo[d][1,3]dioxol-5- amine (MSNBA) were designed. The target substituted 3,4,5-isoxazoles were synthesized using a method for converting isoxazole-containing enamines to nitriles by their treatment with tert-butyl nitrite in the presence of boron trifluoride etherate. Primary bioassay demonstrated the ability of the target compounds to inhibit the proliferation of chronic myelogenous leukemia cells K562 in medium containing fructose or glucose.

The development of antiepileptic drugs remains a serious challenge for both academia and industry. Ionotropic glutamate receptors and voltage-gated sodium channels are among the primary targets of antiepileptic agents. Recent studies have revealed a unique property of phenytoin: unlike other sodium-channel blockers, it inhibits calcium-impermeable AMPA receptors at micromolar concentrations. In this study, we explored the structure–activity relationships of eight phenytoin derivatives. The effects of the compounds on neuronal voltage-gated Na+ channels and neuronal AMPA receptor channels were examined using the patch-clamp technique. For the Na+ channels, we analyzed tonic block, shifts of steady-state inactivation, and frequency-dependent block. For the AMPA receptors, we investigated kinetics, agonist dependence, and trapping effects. NH groups at positions 1 and 3, the carbonyl groups at positions 2 and 4, and the phenyl group at position 5 are important, since their replacement causes a decrease in activity. Replacement of oxygen with sulfur at position 2 results in a significant increase in activity on both types of channels. For the AMPA receptor, this increase is attributable to a more stable drug–channel complex. The enhanced action on sodium channels is due to an increase in tonic block, whereas the effects on inactivated and open channels remain unchanged. These results suggest a new possibility for tuning the activities of phenytoin derivatives against both primary targets to obtain anticonvulsants with novel properties.

Two series of novel 4-nitro-5-styrylisoxazoles (11 compounds) containing various macrocyclic substituents at positions 3 and 5 of the isoxazole cycle were obtained. Isoxazoles with macrocyclic signal unit in the styryl moiety demonstrated sensor properties in organic solvents to a number of metal cations (Mg(II), Ca(II), Zn(II), La(III), Al(III), Pb(II)). Aggregation-induced emission for the obtained dyes was found in the mixture of DMSO/H2O. In the presence of serum albumin, aggregates of macrocyclic styrylisoxazoles in an aqueous medium dissociated into monomers and formed complex with macromolecule. The compounds demonstrated cytoplasmic distribution in cells in two different forms as aggregates with ‘red’ fluorescence and dyes complexes with cellular proteins with ‘green’ fluorescence, which is promising for studying metabolic processes in the cell.

An efficient approach to previously unknown 5-cyano-4-nitroisoxazoles has been developed using nitrosation of 4-nitroisoxazole-based enamines with tert-butyl nitrite (TBN) followed by a BF3- or TFAA-mediated unusual C═C bond cleavage reaction. This two-step one-pot process is applicable to a broad range of substrates and provides the desired products in mild reaction conditions in moderate to high yields. The dichotomy of reactivity in the SNAr reaction of the resulting 5-cyano-4-nitroisoxazoles has been demonstrated by the cyano-group substitution with N-nucleophiles and the nitro-group substitution with thiophenols and rationalized with DFT-calculations.

A facile metal-free approach to 5-(1,2,3-triazol-1-yl)isoxazoles bearing a variety of functional groups in both heterocyles has been developed. A cyclization of 3-EWG-5-azidoisoxazoles with compounds possessing active methylene group proceeds smoothly under mild conditions in the presence of triethylamine or Cs2CO3 in alcohols or DMF affording fused hybrid triazole-isoxazole compounds in high yields up to 98%. Some mechanistic aspects of the cyclization reaction are discussed.

ABSTRACT A large series of previously unknown isoxazole containing difluoroboron β‐diketonate has been designed and synthesized from the available starting compounds. The photophysical properties of obtained compounds were studied, and the effects of the substituents in aromatic and isoxazole cycles of the BF 2 complexes on the fluorescence were investigated. The effect of solvatochromism were demonstrated. Cytotoxic activity against MCF‐7 (breast carcinoma), HCT‐116 (colon carcinoma), A549 (pulmonary carcinoma) and WI38 (fibroblasts from lung tissue) cell lines was tested and moderate toxicity in the concentration range of 10–100 μM was found for several compounds.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Spirocyclic compounds containing heterocyclic moieties represent promising 3D scaffolds for modern drug design. In the search for novel anti-flaviviral agents, we have obtained a series of 3-[N,N-bis(sulfonyl)amino]isoxazolines containing spiro-annulated cyclooctane rings and assessed their antiviral activity against tick-borne encephalitis (TBEV), yellow fever (YFV), and West Nile (WNV) viruses. The structural analogs of spirocyclic compounds with a single sulfonyl group or 1,2-annulated cyclooctane ring were also investigated. Almost all the studied 3-[N,N-bis(sulfonyl)amino]isoxazolines revealed antiviral activity against TBEV and WNV. The most active against TBEV was spiro-isoxazoline derivative containing p-nitrophenyl groups in the sulfonyl part (EC50 2.0 ± 0.5 μM), while the highest potency against WNV was found for the compounds with lipophilic substituents in sulfonyl moiety, naphtyl being the most favorable one (EC50 1.3 ± 0.5 μM). In summary, two novel scaffolds of anti-flaviviral agents based on N,N-bis(sulfonyl)amino]isoxazoline were proposed, and the compounds of this type demonstrated activity against TBEV and WNV.

A simple two-step protocol for the synthesis of 3-aryl/hetaryl-4-nitro-5-styrylisoxazole was elaborated. A large series of novel 5-styrylisoxazoles (36 compounds) containing various substituents at positions 3 and 5 of isoxazole cycle was obtained. The title compounds revealed fluorescent properties in visible region, possessing emission maximum up to 610nm. The effect of solvatochromism and chemosensor properties towards a number of metal cations were demonstrated. Cytotoxic activity against MCF-7 (breast carcinoma), HCT-116 (colon carcinoma), A549 (pulmonary carcinoma) and WI38 (fibroblasts from lung tissue) cell lines was tested and toxicity in the concentration range of 10-100 mu M was found for several compounds.

A method for the synthesis of 4-methyl-2-oxo-9-phenyl-2 H -furo[2,3- h ]chromene-8-carboxylic acid amides combining in the structure the angelicin core with heterocyclic fragments at the amide nitrogen atom was developed. The cytotoxic activity of the obtained amides against the MCF7 (breast adenocarcinoma), A549 (non-small cell lung cancer), VA-13 (embryonic lung fibroblast cells) and HEK293T (embryonic kidney cells) cell lines was studied. In contrast to the previously described highly toxic angelicin derivatives with aryl- and hetarylcarbonyl substituents at position 8, the synthesized amides demonstrated in in vitro experiments in these cell lines the IC 50abs values ranging within 2–100 µmol L −1 . The cytotoxicity and selectivity of the action of this group of derivatives were found to be significantly affected by the substituent at position 5′ of the angelicin moiety.

A series of podophyllotoxin and epipodophyllotoxin esters with methylisoxazole fragments containing a halogen atom or a nitro group at position 4 of the heterocycle was synthesized. The starting isoxazolecarboxylic acids were obtained by bromination, iodination, or nitration of 5-methylisoxazole-3-carboxylic acid, which then were converted to the target esters by esterification in the DCC/DMAP or EDC/DMAP system. The results of molecular docking of podophyllotoxin and epipodophyllotoxin esters with the iodine-containing isoxazole derivatives predicted their ability to bind to tubulin and topoisomerase II, respectively, and do not exclude the possibility of the formation of halogen bonds with target proteins. The primary bioscreening showed that all compounds obtained at a concentration of 100 nmol L-1 caused a decrease in the number of A549 and VA13 cells by 40-60% after 72 h of treatment.

An efficient regioselective approach to novel functionalized bis(isoxazoles) with a variety of aromatic and aliphatic linkers was elaborated, based on the heterocyclization reaction of electrophilic alkenes under the treatment with tetranitromethane-triethylamine complex affording 3-EWG-5-nitroisoxazoles. The subsequent SNAr reactions of 5-nitroisoxazoles with various O,O-, N,N- and S,S-bis(nucleophiles) provide a wide range of bis(isoxazole) derivatives in good isolated yields. Employing an elaborated method, a series of novel bis(3-EWG-isoxazoles) as the promising allosteric modulators of AMPA receptors were designed and synthesized. The effect of the compounds on the kainate-induced currents was studied in the patch clamp experiments, revealing modulator properties for several of them. The best positive modulator potency was found for dimethyl 5,5′-(ethane-1,2-diylbis(sulfanediyl))bis(isoxazole-3-carboxylate), which potentiated the kainate-induced currents in a wide concentration range (10−12–10−6 M) with maximum potentiation of 77% at 10−10 M. The results were rationalized using molecular docking and molecular dynamics simulations of modulator complexes with the dimeric ligand-binding domain of the GluA2 AMPA receptor. The predicted physicochemical, ADMET, and PAINS properties confirmed that the AMPA receptor modulators based on the bis(isoxazole) scaffold may serve as potential lead compounds for the development of neuroprotective drugs.

Water-dispersible complexes of 4-methyl-N-[5-methyl-3-(3,4,5-trimethoxyphenyl)isoxazol-4-yl]benzamide possessing anticancer activity were prepared by its immobilization with biocompatible polymer nanocontainers based on sodium alginate cross-linked with Ca2+ and Mg2+ ions. It was found that this isoxazole derivative retains its structure during immobilization. Colloidal stable nanocontainers filled with this compound exhibit toxicity toward the colon carcinoma (HCT116) tumor cell line.

NMDA (N-methyl-d-aspartate) receptor antagonists are promising tools for the treatment of a wide variety of central nervous system impairments including major depressive disorder. We present here the activity optimization process of a biphenyl-based NMDA negative allosteric modulator (NAM) guided by free energy calculations, which led to a 100 times activity improvement (IC50 = 50 nM) compared to a hit compound identified in virtual screening. Preliminary calculation results suggest a low affinity for the human ether-a-go-go-related gene ion channel (hERG), a high affinity for which was earlier one of the main obstacles for the development of first-generation NMDA-receptor negative allosteric modulators. The docking study and the molecular dynamics calculations suggest a completely different binding mode (ifenprodil-like) compared to another biaryl-based NMDA NAM EVT-101.

Since isoxazole and triazole have significant applications in pharmaceutical chemistry, the synthesis of hybrid isoxazole-triazole molecules has attracted great attention. In the present study, an efficient method for the synthesis of 5-azidoisoxazoles has been developed via chemoselective nitro-group substitution of 3-EWG-5-nitroisoxazoles with sodium azide through the aromatic nucleophilic substitution reaction. The resulting 5-azidoisoxazoles are employed in CuACC-reaction with a variety of alkynes, providing a straightforward approach for the synthesis of previously unknown structure type of biologically relevant 5-(1,2,3-triazol-1-yl)isoxazoles. Both reactions proceed with excellent yields and functional group tolerance under mild conditions.

A series of novel antimitotic agents was designed using the replacement of heterocyclic cores in two tubulin-targeting lead molecules with the acylated 4-aminoisoxazole moiety. Target compounds were synthesized via heterocyclization of β-aryl-substituted vinylketones by tert-butyl nitrite in the presence of water as a key step. 4-Methyl-N-[5-methyl-3-(3,4,5-trimethoxyphenyl)isoxazol-4-yl]benzamide (1aa) was found to stimulate partial depolymerization of microtubules of human lung carcinoma A549 cells at a high concentration of 100 µM and to totally inhibit cell growth (IC50  = 0.99 µM) and cell viability (IC50  = 0.271 µM) in the nanomolar to submicromolar concentration range. These data provide evidence of the multitarget profile of the cytotoxic action of compound 1aa. The SAR study demonstrated that the 3,4,5-trimethoxyphenyl residue is the key structural parameter determining the efficiency both towards tubulin and other molecular targets. The cytotoxicity of 3-methyl-N-[5-methyl-3-(3,4,5-trimethoxyphenyl)isoxazol-4-yl]benzamide (1ab) to the androgen-sensitive human prostate adenocarcinoma cancer cell line LNCaP (IC50  = 0.301 µM) was approximately one order of magnitude higher than that to the conditionally normal cells lines WI-26 VA4 (IC50  = 2.26 µM) and human umbilical vein endothelial cells (IC50  = 5.58 µM) and significantly higher than that to primary fibroblasts (IC50  > 75 µM).

An efficient protocol for the straightforward functionalization of the isoxazole ring via the reactions of aromatic nucleophilic substitution of the nitro group with various nucleophiles has been elaborated. The method features excellent chemical yields, easy operability of the reaction, mild reaction conditions and a broad scope of both 5-nitroisoxazoles and nucleophiles. A synthetic approach to 3,5- and 3,4,5-substituted isoxazoles via the sequential functionalization of the isoxazole ring has been developed based on the excellent regioselectivity of the reaction of 3,5-dinitroisoxazoles with nucleophiles.