The recent progress of isoxazole in medicinal chemistry

Mechanisms and Origins of Regio- and Stereoselectivities in NHC-Catalyzed [3 + 3] Annulation of α-Bromoenals and 5-Aminoisoxazoles: A DFT Study

Density functional theory (DFT) calculations were conducted to explore the mechanisms and origins of regio- and stereoselectivities underlying the [3 + 3] annulation reaction between α-bromoenals and 5-aminoisoxazoles with N-heterocyclic carbene (NHC) as the catalyst. The reaction occurs in nine steps: (1) nucleophilic addition of NHC to α-bromoenal, (2) Breslow intermediate formation through 1,2-proton transfer, (3) debromination, (4) α,β-unsaturated acyl azolium intermediate formation via 1,3-proton transfer, (5) addition of α,β-unsaturated acyl azolium intermediate to 5-aminoisoxazole, (6) deprotonation, (7) protonation, (8) ring closure, and (9) elimination of NHC. For the fifth step, 1,2-addition suggested in the experiment was not supported by our results. Instead, we found that Michael addition is energetically the most feasible pathway and the stereo-controlling step that preferentially provides the S-configuration product. DFT-computed results and experimental findings agree well. Analysis of distortion/interaction reveals that lower distortion energy leads to stability of the transition state corresponding to the S-configuration product. Global reactivity index analysis indicates that the behavior of the NHC catalyst differs significantly before and after the Breslow intermediate debromination. Before debromination, the nucleophilicity of α-bromoenal is enhanced by addition to NHC. However, after debromination, the α,β-unsaturated acyl azole generates and acts as an electrophilic reagent.

Exploring the impact of trifluoromethyl (-CF3) functional group on the anti-cancer activity of isoxazole-based molecules: design, synthesis, biological evaluation and molecular docking analysis

Herein we report the design and synthesis of a series of fully-substituted 4-(trifluoromethyl)isoxazoles and evaluation of their anti-cancer activities against MCF-7, 4T1 and PC-3 cell lines as a proof of concept study. 4-(Trifluoromethyl)isoxazole is a synthetically challenging class of molecules and very few synthetic methods have been developed so far and all of them suffered from several serious limitations. Recently we developed a novel, metal-free, and general synthetic strategy to access synthetically challenging 4-(trifluoromethyl)isoxazoles starting from readily available chalcones using cheap CF3SO2Na as the source of the -CF3 group and multitasking t BuONO as an oxidant as well as the source of N and O and thus we have overcome the limitations of the previous methods. Based on the structure of an isoxazole-based anti-cancer agent, 3-(3,4-dimethoxyphenyl)-5-(thiophen-2-yl)isoxazole 14, we designed a set of 4-(trifluoromethyl)isoxazoles for synthesis and further anti-cancer evaluation. Among various molecules, 3-(3,4-dimethoxyphenyl)-5-(thiophen-2-yl)-4-(trifluoromethyl)isoxazole 2g (IC50 = 2.63 μM) and 3-(thiophen-2-yl)-5-(4-(thiophen-2-yl)-1H-pyrrol-3-yl)-4-(trifluoromethyl)isoxazole 5 (IC50 = 3.09 μM) exhibited the best anti-cancer activity against the human breast cancer cell-lines (MCF-7), 2g being the lead molecule among all. Interestingly, 2g is found to be almost 8 times more active compared to its non-trifluoromethylated analogue, i.e., 3-(3,4-dimethoxyphenyl)-5-(thiophen-2-yl)isoxazole 14 (IC50 = 19.72 μM) which revealed the importance of a 'CF3' moiety in enhancing the anti-cancer activity of 14. Further studies such as apoptosis induction, cell cycle analysis, and nuclear staining revealed an apoptotic cell death mechanism. The in silico molecular docking, induced fit analysis, and ADME studies further supported the effect of a -CF3 moiety on the enhancement of anti-cancer activity of isoxazole-based anti-cancer molecules. Further exploration of the biodistribution and therapeutic efficacy of lead 2gin vivo holds significant promise, positioning it as a potential candidate for anticancer therapy.

Targeting hematological malignancies with isoxazole derivatives

Compounds with a heterocyclic isoxazole ring are well known for their diverse biologic activities encompassing antimicrobial, antipsychotic, immunosuppressive, antidiabetic and anticancer effects. Recent studies on hematological malignancies have also shown that some of the isoxazole-derived compounds feature encouraging cancer selectivity, low toxicity to normal cells and ability to overcome cancer drug resistance of conventional treatments. These characteristics are particularly promising because patients with hematological malignancies face poor clinical outcomes caused by cancer drug resistance or relapse of the disease. This review summarizes the knowledge on isoxazole-derived compounds toward hematological malignancies and provides clues on their mechanism(s) of action (apoptosis, cell cycle arrest, ROS production) and putative pharmacological targets (c-Myc, BET, ATR, FLT3, HSP90, CARM1, tubulin, PD-1/PD-L1, HDACs) wherever known.

Theoretical screening of N-[5'-methyl-3'-isoxasolyl]-N-[(E)-1-(-2-thiophene)] methylidene]amine and its isoxazole based derivatives as donor materials for bulk heterojunction organic solar cells: DFT and TD-DFT investigation

CONTEXT

In the present work, the influence of aromatic ring substitution on a series of small-donor organic molecules (A, B, C, D, and E) with isoxazole cores was investigated for photovoltaic applications in organic solar cells. Frontier molecular orbital analysis, chemical reactivity descriptors, dipole moment, and population analysis showed that all the organic materials have intramolecular charge transfer abilities capable of donating electrons to the acceptor material (PCBM). The required photovoltaic parameters such as Voc, FF, Jsc, LHE, and other associated optoelectronic parameters are reported. The results demonstrate that aromatic ring substitution influences charge transfer and power conversion efficiencies of solar cells. That is, an increase in the aromatic character of a material increases its charge transfer, and as a result, its photovoltaic properties are increased. Additionally, all the investigated derivatives are good charge transporters with suitable electron reorganization energies, which are beneficial for minimizing energy loss. Hence, these organic derivatives with isoxazole backbones are promising materials and may provide fresh insights into the design of new materials for organic solar cell applications.

METHOD

All calculations were performed using DFT and the ORCA 4.1.0 program package as the main tool for geometry optimization and frequency calculations. The Avogadro 1.2.1 visualization tool was used to prepare all input files executed by ORCA 4.1.0. The BP86, B3LYP, and wB97M series of functionals coupled with the def2/TZVP basis set were employed for geometry optimization. All energy-related calculations were carried out using the M06-2x functional. Multiwfn version 3.7 was used for aromaticity and population analysis. Excited state and UV-visible spectra were simulated using the TD-DFT method at the CAM-B3LYP-D3, wB97X-D3, and PBE0-D3 coupled with the ma-def2-TZVP basis set. Moreover, solvent effects were incorporated using the SMD scheme as incorporated in the ORCA software. Lastly, the RIJCOSX approximations were used to speed up calculations while maintaining accuracy.

Palladium-Catalyzed Carbohalogenation of Olefins with Alkynyl Oxime Ethers: Rapid Access to Chlorine-Containing Isoxazoles

A palladium-catalyzed carbohalogenation of olefins with alkynyl oxime ethers has been described, which provides efficient and practical access to various chlorine-containing isoxazoles. This method exhibits excellent regioselectivity, good functional group compatibility, and mild reaction conditions. The mechanistic studies suggest that the reaction proceeds via a stabilized π-benzyl palladium intermediate, which is essential for the formation of C(sp3)-Cl bonds.

A copper-catalyzed asymmetric Friedel-Crafts hydroxyalkylation of pyrazole-4,5-diones with 5-aminoisoxazoles

An asymmetric Friedel-Crafts hydroxyalkylation reaction of 5-aminoisoxazoles with pyrazole-4,5-diones was developed under the catalysis of 5% chiral copper complexes. This reaction exhibits functional group tolerance and excellent enantioselectivity. Moreover, the reaction can be scaled up and its mechanism was studied.

Synthesis of 3,5-disubstituted isoxazoles by domino reductive Nef reaction/cyclization of β-nitroenones

β-Nitroenones can be efficiently converted into 3,5-disubstituted isoxazoles by using tin(II)chloride dihydrate and ethyl acetate as a reducing agent and solvent, respectively. Products are obtained in good yields and several functional groups are tolerated thanks to the mild reaction conditions.

Acridine-Isoxazole and Acridine-Azirine Hybrids: Synthesis, Photochemical Transformations in the UV/Visible Radiation Boundary Region, and Anticancer Activity

Easy-to-handle N-hydroxyacridinecarbimidoyl chloride hydrochlorides were synthesized as convenient nitrile oxide precursors in the preparation of 3-(acridin-9/2-yl)isoxazole derivatives via 1,3-dipolar cycloaddition with terminal alkynes, 1,1-dichloroethene, and acrylonitrile. Azirines with an acridin-9/2-yl substituent attached directly or via the 1,2,3-triazole linker to the azirine C2 were also synthesized. The three-membered rings of the acridine-azirine hybrids were found to be resistant to irradiation in the UV/visible boundary region, despite their long-wave absorption at 320-420 nm, indicating that the acridine moiety cannot be used as an antenna to transfer light energy to generate nitrile ylides from azirines for photoclick cycloaddition. The acridine-isoxazole hybrids linked at the C9-C3 or C2-C3 atoms under blue light irradiation underwent the addition of such hydrogen donor solvents, such as, toluene, o-xylene, mesitylene, 4-chlorotoluene, THF, 1,4-dioxane, or methyl tert-butyl ether (MTBE), to the acridine system to give the corresponding 9-substituted acridanes in good yields. The synthesized acridine-azirine, acridine-isoxazole, and acridane-isoxazole hybrids exhibited cytotoxicity toward both all tested cancer cell lines (HCT 116, MCF7, and A704) and normal cells (WI-26 VA4).

Design, synthesis, In-vitro, In-silico and DFT studies of novel functionalized isoxazoles as antibacterial and antioxidant agents

A series of new isoxazolederivatives incorporating the sulfonate ester function has been synthesized from 2-benzylidenebenzofuran-3(2 H)-one, known as aurone. The synthesis of the target compounds was carried out following an efficient methodology that allows access to the desired products in a reproducible way and with good yield. The structures of the synthesized compounds were established using NMR (1H and 13C) spectroscopy and mass spectrometry. A theoretical study was performed to optimize the geometrical structures and to calculate the structural and electronic parameters of the synthesized compounds. The calculations were also carried out to understand the influence and the effect of substitutions on the chemical reactivity of the studied compounds. The synthesized isoxazoles were screened for their antioxidant and antibacterial activities. The findings demonstrate that the studied compounds exhibit good to moderate antibacterial activity against the tested bacteria (Staphylococcus aureus, Bacillus subtilis, and Escherichia coli). Moreover, a number of the tested isoxazole derivatives exhibit high effectiveness against DPPH free radicals. Besides that, molecular docking studies were carried out to predict binding affinity and identify the most likely binding interactions between the active molecules and the target microorganisms' proteins. A 100 ns molecular dynamics study was then conducted to examine the dynamic behavior and stability of the highly potent isoxazole 4e in complex with the target bacterial proteins. Finally, the ADMET analyses suggest that all the synthesized isoxazoles have good pharmacokinetic profiles and non-toxicity and non-carcinogenicity in biological systems.

Palladium-Catalyzed Cyclization/Alkenylation of Ynone Oximes with Vinylsilanes for the Assembly of Isoxazolyl Vinylsilanes

A palladium-catalyzed cascade cyclization/alkenylation for the assembly of synthetically valuable isoxazolyl vinylsilane derivative has been accomplished. Easily accessible ynone oximes, and available vinylsilane agents were used as the reaction starting materials This protocol features broad substrate scope, good functional group tolerance, and good step- and atom-economy. Remarkably, this approach provides a new approach for the construction of structurally diverse isoxazolyl-containing vinylsilanes with high molecular complexity, showing a promising application in synthetic and pharmaceutical chemistry.

Iodobenzene-Catalyzed Synthesis of Fully Functionalized NH-Pyrazoles and Isoxazoles from α,β-Unsaturated Hydrazones and Oximes via 1,2-Aryl Shift

An iodine(III)-catalyzed general method for the synthesis of fully functionalized NH-pyrazoles and isoxazoles from α,β-unsaturated hydrazones and oximes, respectively, via cyclization/1,2-aryl shift/aromatization/detosylation, has been developed. The reaction progresses through an anti-Baldwin 5-endo-trig cyclization. It gives direct access to an advanced intermediate for the preparation of valdecoxib and parecoxib, drugs used for COX-inhibition. In addition, a method for N-alkynylation of pyrazoles has also been developed in the presence of TIPS-EBX.

Naphtho[1,8-de][1,2]Oxazin-4-ol: Precursor to 1,2,8-Trisubstituted Naphthalenes and 1-Unsubstituted Naphtho[1,2-d]isoxazole 2-Oxide: A Novel Isomerization of the N-Oxide to Nitrile Oxide en Route to Isoxazol(in)es

Naphtho[1,8-de][1,2]oxazin-4-ol and its acyl or benzyl derivatives ring open to various 2,8-dihydroxy-1-naphthonitriles, which, through (de)protection protocols and reduction, afford the target (E)-2-hydroxy-8-methoxy-1-naphthaldehyde. This was converted to its corresponding oxime, which was oxidatively o-cyclized with phenyliodine(III) diacetate (PIDA) to 9-methoxynaphtho[1,2-d]isoxazole 2-oxide. The latter, in deuterated DMSO at room temperature, was rearranged to its isomer 2-hydroxy-8-methoxy(naphthalen-1-yl)nitrile oxide. The isomerization was detected by time-course plot 1H NMR spectroscopy and further identified from its 13C NMR and HRMS spectra. The nitrile oxide was stable in (non)deuterated DMSO for at least 18 h. A 3,4-bis(2-hydroxy-8-methoxynaphthalen-1-yl)-1,2,5-oxadiazole 2-oxide, as a dimerization product or an isocyanate as a rearrangement isomer, was ruled out, the former by its HRMS spectrum and the latter by its 1,3-dipolar cycloaddition reactions to substituted isoxazoles.

Discovery of a new dihydroeugenol-chalcone hybrid with cytotoxic and anti-migratory potential: A dual-action hit for cancer therapeutics

Cancer still represents a serious public health problem and one of the main problems related to the worsening of this disease is the ability of some tumors to develop metastasis. In this work, we synthesized a new series of chalcones and isoxazoles derived from eugenol and analogues as molecular hybrids and these compounds were evaluated against different tumor cell lines. This structural pattern was designed considering the cytotoxic potential already known for eugenol, chalcones and isoxazoles. Notably, chalcones 7, 9, 10, and 11 displayed significant activity (4.2-14.5 µM) against two cancer cell lines, surpassing the potency of the control drug doxorubicin. The reaction of chalcones with hydroxylamine hydrochloride provided the corresponding isoxazoles that were inactive against these cancer cells. The dihydroeugenol chalcone 7 showed the most promising results, demonstrating higher potency against HepG2 (CC50: 4.2 µM) and TOV-21G (CC50: 7.2 µM). Chalcone 7 was also three times less toxic than doxorubicin considering HepG2 cells, with a selectivity index greater than 11. Further investigations including clonogenic survival, cell cycle progression and cell migration assays confirmed the compelling antitumoral potential of chalcone 7, as it reduced long-term survival due to DNA fragmentation, inducing cell death and inhibiting HepG2 cells migration. Moreover, in silico studies involving docking and molecular dynamics revealed a consistent binding mode of chalcone 7 with metalloproteinases, particularly MMP-9, shedding light on its potential mechanism of action related to anti-migratory effects. These significant findings suggest the inclusion of compound 7 as a promising candidate for future studies in the field of cancer therapeutics.

N-Trifluoromethylselenophthalimide, an Electrophilic Trifluoromethylselenolation Reagent and Its Application for the Synthesis of 4-Trifluoromethylselenolated Isoxazoles

A new electrophilic trifluoromethylselenolation reagent, N-trifluoromethylselenophthalimide (Phth-SeCF3), was developed. A strategy for the synthesis of 4-trifluoromethylselenolated isoxazoles through electrophilic trifluoromethylselenolation cyclization has been established by using Phth-SeCF3 as an electrophilic reagent. Moreover, this protocol has the features of broad substrate scope, good functional group tolerance, and high yields.

Organocatalytic Asymmetric Direct Vinylogous Michael Initiated Ring Closure Reaction of 4-Nitroisoxazole Derivatives to 3-Isopropylidene Oxindoles

Herein, we present the first ever use of 3-isopropylidene oxindoles as electrophiles in vinylogous Michael initiated ring closure reaction (MIRC). Among the various alkylidene oxindoles used in enantioselective spirocyclization reactions, isopropylidene oxindoles are the least explored to date. The competing reactivity of isopropylidene oxindoles (electrophilicity vs nucleophilicity) in the presence of a chiral organocatalyst is controlled by the logical selection of a more reactive nucleophile. The methodology produces a library of densely substituted highly enantioenriched spirocyclopropyl oxindoles with excellent yield and stereoselectivities. Moreover, the first enantioselective synthesis of HIV-1 NNRT inhibitor indicates the importance of our synthesized spiro-cyclopropyl oxindole core.

Synthesis, crystal structure and molecular docking study of novel isoxazole derivatives as CYP450 inhibitors in search of anticancer agents

Synthesis of some novel isoxazole derivatives and their molecular docking with enzymes from CYP450 family carried out using erlotinib, gemcitabine and ketoconazole as reference drugs are reported in this work. Eight isoxazole derivatives of 3,4-substituted phenyl 3-chloroacrylaldehyde and one isoxazole derivative of cinnamaldehyde were synthesized. A molecular docking study of all nine compounds shows good docking score compared to standard drugs erlotinib, gemcitabine and ketoconazole. 4-OH and 4-F derivatives were found to have strong affinity for all six CYP450 proteins under study in the present work. 4-F and 3-NO2 derivatives could be a suitable lead compound inhibitor to CYP1A2 followed by 4-OH derivatives. 4-OH derivative with significant binding affinity showed encouraging inhibition of CYP1A2, CYP2C9, CYP2C8, CYP2C19 and CYP2D6. The current predictions over these nine isoxazole derivatives of 3,4-substituted phenyl 3-chloroacrylaldehyde will be needed to be further investigated in vivo and in vitro conditions to identify the optimum therapeutic efficacy. Synthesis of the isoxazole derivatives is the first known report of the Knoevenagal condensation of acrylaldehyde derivatives to form isoxazole derivatives as per the literature survey. A detailed crystal structure study of five analogues gives insight into the solid-state structural features of this new framework with isoxazole moieties.Communicated by Ramaswamy H. Sarma.

Construction of Highly Functionalized C4-Oxyacylated and Aminated Pyrazolines

Pyrazolines and pyrazolones are prevalent cores in drugs and bioactive molecules. Functionalizing them with heteroatoms on the ring improves or expands their clinical efficacy. However, a general method to selectively heterofunctionalize them at C4 and C5 is still elusive. Herein, we have demonstrated an iodine(III)-mediated construction of C4-heterofunctionalized pyrazolines from α,β-unsaturated hydrazones. The oxyacylated and aminated products, bearing a tertiary as well as a secondary stereocenter, were obtained via aza-Michael, followed by a C-O/C-N bond formation. A deprotection/oxidation sequence produced pyrazolones in a quantitative yield.

N2 modified cap analogues as translation inhibitors and substrates for preparation of therapeutic mRNA

In recent years many scientists have begun to focus on the mRNA molecule's emeregence as a new type of drug. Its fast-moving and successful career as a vaccine technology cannot be underestimated. mRNA provides new opportunities and allows for the rapid preparation of effective drugs at low cost. These extensive possibilities stem from a number of factors, but the small cap structure located at the 5' end of the mRNA is one contributing factor. Cap protects mRNA and ensures efficient recruitment to the biosynthesis machinery. Furthermore, it allows for the easy introduction of various modifications that influence the activity of the entire mRNA. Among the many different cap analogues that have been reported, those modified at the N2 position of guanosine have been systematically developed. N2-modified caps in the form of nucleoside monophosphates or dinucleotides show favorable biological properties, as well as a high capacity to inhibit the translation process in the cell-free RRL system. Modified N2 dinucleotides are efficiently incorporated into the structure of the mRNA transcript, and in specific circumstances with the correct orientation, making them an interesting alternative for ARCA-type analogues. Moreover, mRNA transcripts containing cap structures modified within the exocyclic amino group show very high translational activity. Therefore, analogues modified at the N2 position may have future applications as therapeutics against various manifestations of cancer and as desirable tools in RNA engineering.

Primary nitro compounds: progress in the synthesis of isoxazoles by condensation with aldehydes or activated ketones

Among the known strategies directed towards the synthesis of isoxazole derivatives, the reactions of aldehydes with primary nitro compounds deserve a comprehensive treatment, including the historical development as well as the more recent applications. The reactions of aldehydes with primary nitro compounds in a 1 : 2 molar ratio have been shown to lead to isoxazoline-N-oxides or isoxazole derivatives, via β-dinitro derivatives. Several modifications of the process allowed the formation of products bearing substituents at various positions of the heterocyclic ring with control of regioselectivity. Ketones are reported to react with primary nitro compounds, only if activated (β-diketones, α-nitroketones, or strained ketones), to give isoxazole derivatives. Symmetric 2,4-dinitroglutarates formed from aromatic aldehydes and nitroacetate undergo ring closure to form isoxazole derivatives or, according to reaction conditions, 5-hydroxy-6-oxo-4-aryl-6H-1,2-oxazine-3-carboxylates ("oxazinones"), by loss of alcohol instead of water. Isoxazole-4-carbaldehydes are obtained by the reaction of 3-oxetanone with primary nitro compounds.

Synthesis of gem-Difluorinated Isoxazoles via Palladium-Catalyzed Oxylallylation of Alkynone Oxime Ethers

A novel and reliable palladium-catalyzed oxylallylation of alkynone oxime ethers with fluorine-containing alkenes was accomplished. Using the bulk industrial chemical 3-bromo-3,3-difluoroprop-1-ene as the coupling partner, this synthetic methodology offers the first example for the assembly of structurally diverse gem-difluorinated isoxazole derivatives in moderate to good yields with high atom- and step-economy and excellent functional group compatibility. More importantly, this strategy allows for the direct combination of the isoxazole motifs and gem-difluoroalkene unit, which is not easy to obtain through a general synthetic strategy.

Synthesis, in-vitro inhibition of cyclooxygenases and in silico studies of new isoxazole derivatives

Isoxazole belongs to the class of five-membered heterocyclic compounds. The process of developing new drugs has significantly gained attention due to inadequate pharmacokinetic and safety attributes of the available drugs. This study aimed to design a new diverse array of ten novel isoxazole derivatives via Claisen Schmidt condensation reaction. In vitro COX-1/2 anti-inflammatory assay, in silico molecular docking of potent compounds, Molecular docking simulation, and SwissADME pharmacokinetic profile were investigated in this research. The in vitro COX-1 and COX-2 enzyme inhibitory assay showed that almost all the tested compounds exhibited anti-inflammatory effects whereas C6, C5, and C3 were found to be the most potent COX-2 enzyme inhibitors among the tested compounds and are good candidates for selective COX-2 inhibitors. In silico molecular docking studies coupled with molecular dynamic simulation has been done to rationalize the time-evolved mode of interaction of selected inhibitor inside the active pockets of target COX-2. The binding orientations and binding energy results also showed the selectivity of compounds towards COX-2. Physicochemical properties, pharmacokinetic profile, lipophilicity, water solubility, drug metabolism, drug-likeness properties, and medicinal chemistry of the synthesized isoxazole derivatives were assessed. The SwissADME (absorption, distribution, metabolism, and excretion) database was used to assess the physicochemical properties and drug-likeness properties of the synthesized isoxazole derivatives. All the compounds were shown high GI absorption except Compound 7 (C7). Compound 1 (C1) and Compound 2 (C2) were found to cross the blood-brain barrier (BBB). Lipinski's rule of five is not violated by any of the ten synthesized isoxazole derivatives. It was predicted with the SwissADME database that C2, C5, C6, C7, and C8 are potent inhibitors of cytochrome (CYP) subtype CYP-2C19. A subtype of CYP-2C9 was inhibited by C4 and C7. The medicinal chemistry of all the compounds C1-C10 showed no PAIN (Pan assay interference compounds) alerts. The improved gastrointestinal (GI) absorption and BBB permeability of C1 and C2 can provide a future prospective for new researchers in the medicinal field to investigate the compounds for the management of chronic diseases. The synthesized isoxazole compounds showed excellent in vitro COX-1/2 enzymes anti-inflammatory investigations, in silico studies, good physicochemical properties, and improved pharmacokinetic profile which will be further investigated via in vivo anti-inflammatory activities. Moreover, to further support our findings of the computational research and in vitro studies, an in-vivo pharmacokinetic profile is suggested in the future.

Design of novel water-soluble isoxazole-based antimicrobial agents and evaluation of their cytotoxicity and acute toxicity

Based on the readily available 3-organyl-5-(chloromethyl)isoxazoles, a number of previously unknown water-soluble conjugates of isoxazoles with thiourea, amino acids, some secondary and tertiary amines, and thioglycolic acid were synthesized. The bacteriostatic activity of aforementioned compounds has been studied against Enterococcus durans B-603, Bacillus subtilis B-407, Rhodococcus qingshengii Ac-2784D, and Escherichia coli B-1238 microorganisms (provided by All-Russian Collection of Microorganisms, VKM). The influence of the nature of the substituents in positions 3 and 5 of the isoxazole ring on the antimicrobial activity of the obtained compounds has been determined. It is found that the highest bacteriostatic effect is observed for compounds containing 4-methoxyphenyl or 5-nitrofuran-2-yl substituents in position 3 of the isoxazole ring as well as methylene group in position 5 bearing residues of l-proline or N-Ac-l-cysteine (5a-d, MIC 0.06-2.5 µg/ml). The leading compounds showed low cytotoxicity on normal human skin fibroblast cells (NAF1nor) and low acute toxicity on mice in comparison with the well-known isoxazole-containing antibiotic oxacillin.

Methyl 4-amino-3-meth-oxy-isoxazole-5-carboxyl-ate

The title compound, C6H8N2O4, a new derivative of isoxazole, has been synthesized and structurally characterized. The crystal structure shows the mol-ecule to be almost planar (r.m.s. deviation for the non-hydrogen atoms = 0.029 Å), this conformation being supported by an intra-molecular N-H⋯O hydrogen bond. In the extended structure, the mol-ecules are linked by N-H⋯O hydrogen bonds into chains propagating along [010].

Synthesis and Antitumor Activity of Panaxadiol Pyrazole and Isooxazole Derivatives

In this study, we designed and synthesized 19 nitrogen-containing heterocyclic derivatives of panaxadiol (PD). We first reported the antiproliferative activity of these compounds against four different tumor cells. The results of the MTT assay showed that the PD pyrazole derivative (compound 12b) had the best antitumor activity and could significantly inhibit the proliferation of four tested tumor cells. For A549 cells, the IC50 value was as low as 13.44±1.23 μM. Western blot analysis showed that the PD pyrazole derivative was a bifunctional regulator. On the one hand, it can down-regulate the expression of HIF-1α by acting on PI3 K/AKT signaling pathway in A549 cells. On the other hand, it can induce the decrease of CDKs protein family and E2F1 protein expression levels, thus playing a crucial role in cell cycle arrest. According to the results of molecular docking, we found that multiple hydrogen bonds were formed between the PD pyrazole derivative and two related proteins, and the docking score of the derivative was also significantly higher than that of the crude drug. In summary, the study of the PD pyrazole derivative laid a foundation for the development of ginsenoside as an antitumor agent.

Chiral spirocyclic phosphoric acid-catalyzed enantioselective synthesis of heterotriarylmethanes bearing an amino acid moiety

We present herein an enantioselective protocol for the chiral phosphoric acid-catalyzed addition of 3-arylisoxazol-5-amines to highly reactive 3-methide-3H-pyrroles to provide a diverse range of heterotriarylmethanes bearing an amino acid moiety in good yields (up to 97%) and high enantioselectivities (up to 93% ee) under mild conditions. The chiral spirocyclic phosphoric acid is crucial in converting the initial 1H-pyrrol-3-yl carbinols into reactive 3-methide-3H-pyrroles and obtaining the good enantiocontrol, thereby facilitating the desired enantioselective transformation.

Photoinduced Diastereoselective Aminoalkylation of Cubanes

The unique properties of rigid, nonconjugated hydrocarbons provide many opportunities to design molecular building blocks for a variety of applications, but the development of suitable conditions for alkylation of cubanes is quite challenging. Herein, a photoinduced method for aminoalkylation of cubanes is reported. The benign conditions reported allow the incorporation of a wide variety of (hetero)arylimine reaction partners with broad functional group tolerance and high diastereoselectivity.

Magnetic poly(1,8-diaminonaphthalene)-nickel nanocatalyst for the synthesis of antioxidant and antibacterial isoxazole-5(4H)-ones derivatives

A magnetic poly (1,8-diaminonaphthalene)-nickel (PDAN-Ni@Fe₃O₄) composite as a multifunctional nanocatalyst was prepared in several steps including (I) synthesis of poly (1,8-diaminonaphthalene) (PDAN), (II) modification of PDAN with NiSO₄ (PDAN-Ni) and (III) preparation of magnetic nanocatalyst by iron (I and II) salts in the existence of PDAN-Ni complex (PDAN-Ni@Fe₃O₄). Fourier-transform infrared spectroscopy (FTIR), elemental analysis (CHNSO), vibrating-sample magnetometer (VSM), X-ray diffraction (XRD), energy-dispersive X-ray (EDX), field emission scanning electron microscope (FESEM), ultraviolet-visible (UV-vis), and thermogravimetric analysis (TGA) were applied to characterize the prepared nanocatalyst. The PDAN-Ni@Fe₃O₄ was applied as an environmentally friendly nanocatalyst for the isoxazole-5(4H)-ones synthesis via a one-pot reaction between aryl/heteroaryl aldehyde, hydroxylamine hydrochloride, and β-ketoester. The nanocomposite was also used for the synthesis of some new alkylene bridging bis 4-benzylidene-3-methyl isoxazole-5(4H)-ones. The catalyst's reusability, and the antioxidant and antibacterial activities of both catalyst and products, were studied. Results showed that the nanocatalyst and isoxazole-5(4H)-ones have antioxidant activity of 75% and 92%, respectively. In addition, the antibacterial test showed that the nanocatalyst and isoxazole-5(4H)-ones have highly active versus Staphylococcus aureus and Escherichia coli bacteria. The reusability and stability of the nanocatalyst, a medium to higher product yield and conversion, a faster reaction time, and the use of green solvents were a few benefits of this study.

Collision Induced Dissociation of Deprotonated Isoxazole and 3-Methyl Isoxazole via Direct Chemical Dynamics Simulations

Isoxazoles are an important class of organic compounds widely employed in synthesis and drug design. Fragmentation chemistry of the parent isoxazole molecule and its substituents has been the subject of several experimental and theoretical investigations. Collision induced dissociation (CID) of isoxazole and its substituents has been studied experimentally under negative ion conditions. Based on the observed reaction products, dissociation patterns were proposed. In the present work, we studied the dissociation chemistry of deprotonated isoxazole and 3-methyl isoxazole using electronic structure theory calculations and direct chemical dynamics simulations. Various deprotonated isomers of these molecules were activated by collision with an Ar atom, and the ensuing fractionation patterns were studied using on-the-fly classical trajectory simulations at the density functional B3LYP/6-31+G* level of electronic structure theory. A variety of reaction products and pathways were observed, and it was found that a nonstatistical shattering mechanism dominates the CID dynamics of these molecules. Simulation results are compared with experiments, and detailed atomic level dissociation mechanisms are presented.

Isoxazolyl-Derived 1,4-Dihydroazolo[5,1-c][1,2,4]Triazines: Synthesis and Photochemical Properties

New fluorescent dyes containing an assembled 1,4-dihydroazolo[5,1-c][1,2,4]triazine (DAT) core and an isoxazole ring were synthesized through a reaction between diazopyrazole or diazoimidazoles and isoxazolyl-derived enamines in mild conditions. The photophysical characteristics (maxima absorption and emission, Stokes shifts, fluorescent quantum yields, and fluorescence lifetimes) of the new fluorophores were obtained. The prepared DATs demonstrated emission maxima ranging within 433-487 nm, quantum yields within 6.1-33.3%, and a large Stokes shift. The photophysical characteristics of representative DAT examples were studied in ten different solvents. Specific (hydrogen bonds) and non-specific (dipole-dipole) intermolecular and intramolecular interactions were analyzed using XRD data and spectral experiments. Solvatochromism was analyzed using Lippert-Mataga and Dimroth-Reichardt plots, revealing the relationship between the DAT structure and the nature of solute-solvent interactions. The significant advantages of DATs are the fluorescence of their powders (QY up to 98.7%). DAT-NMe₂10 expressed bright aggregation-induced emission (AIE) behavior in DMSO and THF as the water content increased. The numerous possible variations of the structures of the heterocycles included in the DATs, as well as substituents, create excellent prospects for adjusting their photophysical and physicochemical properties.

Synthesis of novel sulphamethoxazole derivatives and exploration of their anticancer and antimicrobial properties

A series of new derivatives based on sulfamethoxazole were designed and synthesized in this study. The structures of the new compounds were confirmed based on a comprehensive characterization of spectral data by applied IR and ¹H as well as ¹³C NMR spectroscopy. The prepared compounds were tested for their anticancer and antimicrobial properties. Hydrazone 16b demonstrated convincing anticancer effect against all tested cell cultures such as human prostate carcinoma PPC-1 and human kidney carcinoma CaKi-1 cell lines, and human fibroblasts HF, n = 3. The most promising compound 16b showed higher activity against CaKi-1 cell line than the anticancer drugs axitinib and pazopanib used to treat renal cancer. Also, it was more active in the PPC-1 cell line compared to the approved PARP inhibitor Olaparib. Hydrazone 16b was also found to possess good antimicrobial properties against gram-positive bacteria strains of Staphylococcus aureus, Staphylococcus epidermidis, as well as Bacillus cereus.

One-Pot Synthesis of Isoxazole-Fused Tricyclic Quinazoline Alkaloid Derivatives via Intramolecular Cycloaddition of Propargyl-Substituted Methyl Azaarenes under Metal-Free Conditions

A practical method was developed for the convenient synthesis of isoxazole-fused tricyclic quinazoline alkaloids. This procedure accesses diverse isoxazole-fused tricyclic quinazoline alkaloids and their derivatives via intramolecular cycloaddition of methyl azaarenes with tert-butyl nitrite (TBN). In this method, TBN acts as the radical initiator and the source of N-O. Moreover, this protocol forms new C-N, C-C, and C-O bonds via sequence nitration and annulation in a one-pot process with broad substrate scope and functionalization of natural products.

Synthesis of (4-Trifluoromethyl)isoxazoles through a Tandem Trifluoromethyloximation/Cyclization/Elimination Reaction of α,β-Unsaturated Carbonyls

We disclose a metal-free, cascade regio- and stereoselective trifluormethyloximation, cyclization, and elimination strategy with readily available α,β-unsaturated carbonyl compounds to access a wide variety of pharmaceutically potential heteroaromatics, i.e., 4-(trifluoromethyl)isoxazoles including a trifluoromethyl analogue of an anticancer agent. The transformation requires only a couple of commercially available and cheap reagents i.e., CF₃SO₂Na as the trifluoromethyl source, and ^tBuONO as an oxidant as well as a source of N and O. Notably, 5-alkenyl-4-(trifluoromethyl)isoxazoles were further synthetically diversified to a new class of biheteroaryls, i.e., 5-(3-pyrrolyl)-4-(trifluoromethyl)isoxazoles. Mechanistic studies revealed a radical pathway for the reaction.

Acid-Switchable Synthesis of Trifluoromethylated Triazoles and Isoxazoles via Reaction of CF3-Ynones with NaN3: DFT Study of the Reaction Mechanism

A detailed study of the reaction of CF₃-ynones with NaN₃ was performed. It was found that the reaction permits the selective synthesis of either 4-trifluoroacetyltriazoles or 5-CF₃-isoxazoles. The chemoselectivity of the reaction was switchable via acid catalysis. The reaction of CF₃-ynones with NaN₃ in EtOH produced high yields of 4-trifluoroacetyltriazoles. In contrast, the formation of 5-CF₃-isoxazoles was observed under catalysis by acids. This acid-switchable procedure can be performed at sub-gram scale. The possible reaction mechanism was supported by DFT calculations. The synthetic utility of the prepared 4-trifluoroacetyltriazoles was demonstrated.

Synthesis and Biological Activity of N-acyl Anabasine and Cytisine Derivatives with Adamantane, Pyridine and 1,2-Azole Fragments

A series of N-acyl derivatives of anabasine and cytisine were prepared, to discover novel, natural product-based medicinal agents. All synthesized compounds were tested for antimicrobial, antifungal, antiviral and analgesic activity. The most pronounced antibacterial activity was shown by the compounds with isoxazole fragments, while the adamantane derivatives showed the greatest antiviral effect. It was found that the majority of anabasine derivatives showed significant analgesic activity, reducing the pain response of animals to the irritating effect of acetic acid. The presence of a high level of antimicrobial and antiviral activity in newly synthesized compounds makes it possible to consider them promising for further study of their pharmacological properties.

Defect Passivation via Isoxazole Doping in Perovskite Solar Cells

To improve perovskite solar cell (PSC) performance, which is deeply related to perovskite layer quality, researchers have explored numerous strategies. Additive doping into perovskite precursors has been widely used to improve the PSC performance. In this study, we used isoxazole-a Lewis-base small molecule-as an additive for the CH₃NH₃PbI₃ (MAPbI₃) precursor and explored how isoxazole effectively passivates defects in the perovskite structure. We found that isoxazole interacted with undercoordinated Pb²⁺ ions from an X-ray photoelectron spectroscopy survey and verified that isoxazole doping improved the device performance. When the optimized concentration of isoxazole was doped in the MAPbI₃ precursor, the power conversion efficiency increased from 15.6 to 17.5%, with an improved fill factor and short-circuit current density. In addition, an isoxazole-doped device sustained 94% of its initial performance after 8 days under ambient air conditions (10 ± 5 RH %, 25 °C), whereas a device without isoxazole doping only maintained 64% of its initial performance.

Isocyanide-Based Multicomponent Reactions in Water: Advanced Green Tools for the Synthesis of Heterocyclic Compounds

Reaction rate acceleration using green methods is an intriguing area of research for chemists. In this regard, water as a "green solvent" plays a crucial role in the acceleration of some organic transformations and reveals exclusive selectivity and reactivity in comparison with conventional organic solvents. In particular, multicomponent reactions (MCRs) as sustainable tools lead to the rapid generation of small-molecule libraries in water and aqueous media due to the prominent role of the hydrophobic effect. MCRs, as diversity-oriented synthesis (DOS) methods, have great efficiency with simple operations, atom, pot, and step economy synthesis, and mechanistic beauty. Among diverse classes of MCRs, isocyanide-based multicomponent reactions (I-MCRs), as sustainable and versatile reactions, have gained considerable attention in the synthesis of diverse heterocycle rings, especially in drug design because of the peculiar nature of isocyanide as a particular active reactant. I-MCRs that are performed in water are mild, environmentally friendly, and easily controlled, and have a reduced number of workup, purification, and extraction steps, which fit well with the advantages of "green" chemistry. Performing these powerful organic transformations in water and aqueous media is accompanied by acceleration owing to negative activation volumes, which originate from connecting several reactants together to generate a single product. It should be noted that the combination of MCR strategy and aqueous phase reaction is of growing interest for the development of sustainable synthetic techniques in organic conversions. However, an exclusive account focusing on the recent progress in eco-friendly I-MCRs for the construction of heterocycles in water and aqueous media is particularly lacking. This review highlights the progress of various kinds of I-MCRs in water and aqueous media as benign methods for the efficient construction of vital heterocyclic scaffolds, with a critical discussion of the subject in the period 2000-2021. We hope that this themed collection will be of interest and beneficial for organic and pharmaceutical chemists and will inspire more reaction development in this fascinating field.

Palladium-Catalyzed Cascade Cyclization/Alkylation of Oxime Ethers: Assembly of 4-Alkylisoxazoles by "Chain-Walking" Strategy

A reliable and efficient palladium-catalyzed cascade cyclization/alkylation of oxime ethers with unactivated alkenes is described, affording a whole variety of structurally diverse isoxazole derivatives in moderate to good yields with excellent functional group compatibility. Ionic liquid [Aeim]Br not only acts as an environmentally friendly solvent but also acts as an accelerating agent to provide excess bromine source to eliminate bromomethane from oxime ethers. More importantly, the use of "chain-walking" strategy provides a novel methodology in organic synthesis to rapid generation of molecular complexity from readily available starting materials.

Harnessing the intrinsic photochemistry of isoxazoles for the development of chemoproteomic crosslinking methods

The intrinsic photochemistry of the isoxazole, a common heterocycle in medicinal chemistry, can be applied to offer an alternative to existing strategies using more perturbing, extrinsic photo-crosslinkers. The utility of isoxazole photo-crosslinking is demonstrated in a wide range of biologically relevant experiments, including common proteomics workflows.

Tyrosol Derivatives, Bearing 3,5-Disubstituted Isoxazole and 1,4-Disubstituted Triazole, as Potential Antileukemia Agents by Promoting Apoptosis

In the present study, we assess tyrosol derivatives bearing 3,5-disubstituted isoxazoles and 1,4-disubstituted triazoles for their ability to inhibit the proliferation of K562 cells derived from leukemia as well as primary chronic myeloid leukemia (CML) cells obtained from the peripheral blood of 15 CML patients including 10 patients with untreated chronic phase and 5 patients with resistance against imatinib or multiple TKI. Our results showed that most derivatives displayed significant anti-proliferative activity against K562 cells in a dose-dependent manner. Among them, compounds 3d and 4a exhibited greater potent anticancer activity with respective IC₅₀ values of 16 and 18 µg/mL (45 µM and 61 µM). Interestingly, compound 3d inhibited CML cell proliferation not only in newly diagnosed but also in imatinib-resistant patients. We demonstrated that the anti-proliferative effect of this compound is mediated by a pro-apoptotic activity by promoting oxidative stress and modulating the activity of the Akt, p38 MAPK and Erk 1/2 pathways. In conclusion, our data highlight the potential of this class of derivative as a novel promising therapeutic agent for CML therapy.

Novel Isoxazole Derivative Attenuates Ethanol-Induced Gastric Mucosal Injury through Inhibition of H+/K+-ATPase Pump, Oxidative Stress and Inflammatory Pathways

Isoxazole derivatives are significant enough due to their wide range of pharmacological and therapeutic activities. The purpose of the current study is to use computational, in vitro, in vivo, and extensive molecular approaches to examine the possible anti-ulcer activity of 4-benzylidene-3 methyl-1,2-isoxazol-5(4H)-one (MBO). Biovia Discovery Studio visualizer (DSV) was utilized for virtual screening. A tissue antioxidant investigation, H⁺/K⁺-ATPase test, and anti-H. pylori activities were carried out. ELISA, immunohistochemistry, and PCR methods were employed for the proteome analysis. An ethanol-induced stomach ulcer model was used to examine the anti-ulcer potential in rats. The binding affinities for MBO ranged from −5.4 to −8.2 Kcal/mol. In vitro findings revealed inhibitory activity against H. pylori and the H⁺/K⁺-ATPase pump. It also enhanced levels of glutathione, catalase, and glutathione-S-transferase and reduced lipid peroxidation levels in gastric tissues of rats. In vivo results showed the gastro-protective effect of MBO (30 mg/kg) in ulcerative rat stomachs. The proteomic study revealed decreased expression of inflammatory markers (cyclooxygenase-2, p-NFkB, and TNF-α). In RT-PCR analysis, the expression levels of H⁺/K⁺-ATPase were reduced. Furthermore, ADMET (absorption, distribution, metabolism, excretion and toxicity) studies revealed that MBO has high GIT solubility and has a safer profile for cardiac toxicity. This study suggests that MBO displayed anti-ulcer potential, which may have been mediated through the inhibition of the H⁺/K⁺-ATPase pump, as well as antioxidant and anti-inflammatory pathways. It has the potential to be a lead molecule in the treatment of peptic ulcers with fewer adverse effects.