Oxazole Derivatives Research Articles

Benzoxazole-terminated liquid crystals with large birefringence and negative dielectric anisotropy

We synthesized heterocyclic liquid crystals with large birefringence and negative dielectric anisotropy, namely, 5–4-(2-(4-(alkoxy)phenyl)-2,3-difluorophenyl)benzo(d)oxazole derivatives (nPFO). These compounds display enantiotropic nematic mesophases with wide mesophase range of 45.9–84.0 °C (heating process) and 61.3–119.6 °C (cooling process). Compared with reference analogues of traditional benzoxazole compound 6PFB with different orientation of benzoxazole-terminated structure, the compounds nPFO roughly give lower melting points and clearing points because of their increased dihedral angle. Meanwhile, compounds nPFO show obviously large birefringence (Δn, 0.28–0.39 and 0.39–0.48 for experimental measurement and DFT theoretical calculation, respectively) due to the enhanced π-conjugation caused by the ethynyl bridge group in molecules. Benefitting from the larger perpendicular dipole moments and orientation angles, nPFO displays negative dielectric anisotropy (Δɛ) ranging from −3.60 to −4.10. These compounds can endow a commercial negative LC mixture the larger Δn and higher values of figure of merit, suggesting they are suitable dopant to further improve the performance of some commercial LC mixtures.

Systematic Photophysical Interaction Studies Between Newly Synthesised Oxazole Derivatives and Silver Nanoparticles: Experimental and DFT Approach.

In this study, the photophysical properties of oxazole derivatives such as 5-(furan-2-yl) -4-tosyloxazole (OX-1) and 5-(2-bromothiazol-4-yl)-4-tosyloxazoles (OX-2) were investigated using theoretical and experimental techniques. The ground and excited state dipole moments were empirically obtained utilising the solvatochromic shift technique and several solvatochromic correlations such as Lippert's, Bakhshiev's, KawskiChamma- Viallet's, and solvent polarity equations. The ground state dipole moments, HOMO-LUMO and molecule electrostatic potential map were also computed using ab initio calculations and evaluated using Gaussian 09 W software. Furthermore, spectroscopic interactions between newly synthesised dyes (OX-1 and OX-2) and freshly synthesised silver nanoparticles (size 40nm) were studied. Increased absorbance and widening of absorption spectra for both dyes in the presence of varied quantities of silver nanoparticles show the potential of dye-nanoparticle interactions. Fluorescence quenching has been detected for both dyes in the presence of colloidal silver nanoparticles, indicating dynamic quenching, and a significant overlap between the absorption and emission spectra of the silver nanoparticle reveals that fluorescence quenching is also due to energy transfer.

Synthesis and Biological Evaluation of Pyrimidin-2-yl)-[1,2,4]triazolo[4,3-a]pyrimidin-3-yl)oxazole Derivatives as Anticancer agents

Synthesis and Biological Evaluation of Pyrimidin-2-yl)-[1,2,4]triazolo[4,3-a]pyrimidin-3-yl)oxazole Derivatives as Anticancer agents

Synthesis, crystal structure, and Hirschfeld surface analysis of novel ethyl 5-bromo-2-(4-methoxyphenyl) oxazole-4-carboxylate

A new oxazole derivative, ethyl 5-bromo-2-(4-methoxyphenyl) oxazole-4-carboxylate, was synthesized and characterized by IR spectroscopy, 13C NMR, Mass spectroscopy, and single-crystal X-ray diffraction analysis. The asymmetric unit of the title compound has two independent molecules (A and B) arranged in an inverted planar orientation, stabilized by intramolecular C-H…O and C-H…N hydrogen bonds and intermolecular C-H…O hydrogen bonds. The crystallographic parameter for the structure C13H12BrNO4 is M =326.15 g/mol, monoclinic, sp. gr. P21/n (no. 14), a = 14.828(2) Å, b = 7.1335(9) Å, c = 25.119(2) Å, β = 100.066(11) °, V = 2616.1(6) Å3, Z = 8. Hirschfeld surface analysis and two-dimensional fingerprint plots provided insight into the short intermolecular interactions, and it was found that H···H (34.4%) interactions contributed the most to the intermolecular interactions. In contrast, the contribution of C · · · C (2.5 %) remained the least among all the interactions.

Computational investigation of imidazo[2,1-b]oxazole derivatives as potential mutant BRAF kinase inhibitors: 3D-QSAR, molecular docking, molecular dynamics simulation, and ADMETox studies

BRAF inhibitors are known to be an effective therapeutic target for treating melanoma and other types of cancer. Using 3D-QSAR, molecular docking, and MD simulations, this study evaluated various imidazo[2,1-b]oxazole derivatives that function as mutant BRAF kinase inhibitors. Comparative molecular field analysis (CoMFA) and comparative molecular similarity index analysis (CoMSIA) were used to create the 3D-QSAR models. CoMSIA/SEHA model has solid predictive power across several models (Q2 = 0.578; R2 = 0.828; R2 pred = 0.74) and is the best model according to the numerous field models generated. The created model’s predictive power was evaluated through external validation using a test set. CoMSIA/SEHA contour maps collect information that can be used to identify critical regions with solid anticancer activity. We developed four inhibitors with high predicted activity due to these observations. ADMET prediction was used to assess the toxicity of the proposed imidazo[2,1-b]oxazole compounds. The predictive molecules (T1-T4) demonstrated good ADMET properties, excluding the toxic active compounds 11r from the database. Molecular docking was also used to determine the patterns and modes of interactions between imidazo[2,1-b]oxazole ligands and receptors, which revealed that the proposed imidazo[2,1-b]oxazole scaffold was stable in the receptor’s active site (PDB code: 4G9C). The suggested compounds (T1-T4) were subjected to molecular dynamics simulations lasting 100 ns to determine their binding free energies. The results showed that T2 had a more favorable binding free energy (−149.552 kJ/mol) than T1 (−112.556 kJ/mol), T3 (−115.503 kJ/mol), and T4 (−102.553 kJ/mol). The results suggest that the imidazo[2,1-b]oxazole compounds investigated in this study have potential as inhibitors of BRAF kinase and could be further developed as anticancer drugs. Highlights 22 imidazo[2,1-b]oxazole compounds were subjected to research on three-dimensional quantitative conformational relationships. Using contour maps from 3D-QSAR models as a guide was used to figure out the areas and strategies for structural optimization. Combined molecular docking, molecular dynamics simulations, and binding free energy calculations to verify the inhibitor activity of the proposed 22 imidazo[2,1-b]oxazole compounds. Four potential B-RAF Kinase inhibitors were discovered, providing theoretical clues for developing a highly anticancer agent. Communicated by Ramaswamy H. Sarma

Design and experimental validation of the oxazole and thiazole derivatives as potential antivirals against of human cytomegalovirus

ABSTRACT QSAR studies of a set of previously synthesized azole derivatives tested against human cytomegalovirus (HCMV) were performed using the OCHEM web platform. The predictive ability of the classification models has a balanced accuracy (BA) of 73–79%. The validation of the models using an external test set proved that the models can be used to predict the activity of newly designed compounds with a reasonable accuracy within the applicability domain (BA = 76–83%). The models were applied to screen a virtual chemical library with expected activity of compounds against HCMV. The five most promising new compounds were identified, synthesized and their antiviral activities against HCMV were evaluated in vitro. Two of them showed some activity against the HCMV strain AD169. According to the results of docking analysis, the most promising biotarget associated with HCMV is DNA polymerase. The docking of the most active compounds 1 and 5 in the DNA polymerase active site shows calculated binding energies of -8.6 and -7.8 kcal/mol, respectively. The ligand’s complexation was stabilized by the formation of hydrogen bonds and hydrophobic interactions with amino acids Lys60, Leu43, Ile49, Pro77, Asp134, Ile135, Val136, Thr62 and Arg137.

New phosphorylated 5-(hydroxyalkylamino)-1,3-oxazoles as potential anticancer agents

Eight new phosphorylated 5-(hydroxyalkylamino)-1,3-oxazoles were designed and tested for their ability to inhibit cancer cell growth. These compounds were evaluated against complete human tumor cell lines NCI-60. Only three compounds showed antitumor activity in the single dose assay, which were taken in the five dose assay. Compounds 7 and 8 showed the same average antiproliferative activity and cytotoxicity against sensitive cell lines of the general panel. However, compound 8 showed cytotoxicity to more lines than 7. By all parameters, these compounds were more active than compounds 5. Compounds 7 and 8 also showed high and similar antiproliferative activity in the concentration range GI50: 1-6 and TGI: 6-14 μM against all subpanels. Their cytotoxicity was in the concentration range of 25-54 μM. Compound 5 showed the same activity, with the exception of the leukemia, non-small cell lung cancer and ovarian cancer subpanels against which their activity was lower. When analyzing the structure-activity, it turned out that among the phosphorylated oxazole derivatives, only compounds containing the triphenylphosphonium cation (TPP+) in the 4th position of the oxazole ring exhibit antitumor activity. Moreover, the replacement of the phenyl radical in the 2nd position of the oxazole scaffold with a methyl radical led to the disappearance of the activity. The COMPARE algorithm reveals a high correlation of the antiproliferative activity of the tested compounds with the antitumor agents phyllantoside and chromomycin A3 in the GI50 vector and moderate with phyllantoside in the TGI vector. The target of all standard drugs that correlate with the cytotoxicity of the studied compounds, with the exception of didemnin, is DNA. Unlike standard compounds, synthesized active compounds carry a delocalized TPP+, which delivers them predominantly to mitochondria due to a much more hyperpolarized potential of the mitochondrial membrane in cancer cells than in normal ones. Therefore, their anticancer activity is most likely due to a disturbation of the structural and functional state of the latter due to interference with their intrinsic protein-synthesizing apparatus of mitochondria. The data obtained allow us to consider 5-(hydroxyalkylamino)-1,3-oxazoles loaded with TPP+ as leading compounds for further in-depth study and synthesis of new TPP+-containing 1,3-oxazole derivatives with antitumor activity

Iodine Mediated One‐Pot Synthesis of Polyarylated‐Oxazoles from Internal Alkynes

AbstractAn environmentally benign, efficient, practically applicable and C(sp3)−H functionalization of primary amines for the synthesis of highly substituted oxazoles from easily available internal alkynes was developed. This synthesis is toxic chemicals, transition‐metal free as well as mild and regioselective. This one‐pot methodology with broad substrate scope unlocks a green avenue for the synthesis of highly functionalized oxazole derivatives with excellent yields.

Photocatalytic Benzylic C-H Oxidation/Cyclization of Enaminones to the Synthesis of Polysubstituted Oxazoles.

Photocatalytic benzylic C-H oxidation/cyclization of enaminones was efficiently achieved to afford oxazole derivatives under mild conditions. The oxygen in the oxazole ring originated from green oxidant molecular oxygen. The synthetic protocol features broad substrate scopes and good functional group tolerance. The combined experimental and theoretical studies reveal that in suit benzylic C-H oxidation/cyclization is involved in the reaction transformations.

An Efficient Synthesis of New Pyrazole‐Linked Oxazoles via Sonogashira Coupling Reaction

AbstractAn efficient method is developed for synthesizing new pyrazole‐linked oxazoles through a palladium‐catalyzed Sonogashira coupling reaction. In this method, from the reaction of 5‐chloro‐3‐methyl‐1‐phenyl‐N‐(prop‐2‐phenyl)‐1H‐pyrazole‐4‐carboxamide with aryl iodides having nitro group and aryl iodides with electron‐donating groups, pyrazole‐linked oxazole derivatives and 5‐chloro‐3‐methyl‐1‐phenyl‐N‐(3‐arylprop‐2‐yn‐1‐yl)‐1H‐pyrazole‐4‐carboxamide derivatives were obtained respectively. The prepared products were characterized using FT‐IR, 1HNMR, and 13CNMR spectroscopies.

Modulation of the 5-Lipoxygenase Pathway by Chalcogen-Containing Inhibitors of Leukotriene A4 Hydrolase.

The 5-lipoxygenase (5-LOX) pathway gives rise to bioactive inflammatory lipid mediators, such as leukotrienes (LTs). 5-LOX carries out the oxygenation of arachidonic acid to the 5-hydroperoxy derivative and then to the leukotriene A4 epoxide which is converted to a chemotactic leukotriene B4 (LTB4) by leukotriene A4 hydrolase (LTA4H). In addition, LTA4H possesses aminopeptidase activity to cleave the N-terminal proline of a pro-inflammatory tripeptide, prolyl-glycyl-proline (PGP). Based on the structural characteristics of LTA4H, it is possible to selectively inhibit the epoxide hydrolase activity while sparing the inactivating, peptidolytic, cleavage of PGP. In the current study, chalcogen-containing compounds, 4-(4-benzylphenyl) thiazol-2-amine (ARM1) and its selenazole (TTSe) and oxazole (TTO) derivatives were characterized regarding their inhibitory and binding properties. All three compounds selectively inhibit the epoxide hydrolase activity of LTA4H at low micromolar concentrations, while sparing the aminopeptidase activity. These inhibitors also block the 5-LOX activity in leukocytes and have distinct inhibition constants with recombinant 5-LOX. Furthermore, high-resolution structures of LTA4H with inhibitors were determined and potential binding sites to 5-LOX were proposed. In conclusion, we present chalcogen-containing inhibitors which differentially target essential steps in the biosynthetic route for LTB4 and can potentially be used as modulators of inflammatory response by the 5-LOX pathway.

Identification of pyrrolo[3′,4’:3,4]cyclohepta[1,2-d][1,2]oxazoles as promising new candidates for the treatment of lymphomas

Unsatisfactory outcomes for relapsed/refractory lymphoma patients prompt continuing efforts to develop new therapeutic strategies. Our previous studies on pyrrole-based anti-lymphoma agents led us to synthesize a new series of twenty-six pyrrolo[3′,4':3,4]cyclohepta[1,2-d] [1,2]oxazole derivatives and study their antiproliferative effects against a panel of four non-Hodgkin lymphoma cell lines. Several candidates showed significant anti-proliferative effects, with IC50's reaching the sub-micromolar range in at least one cell line, with compound 3z demonstrating sub-micromolar growth inhibitory effects towards the entire panel. The VL51 cell line was the most sensitive, with an IC50 value of 0.10 μM for 3z.Our earlier studies had shown that tubulin was a prominent target of many of our oxazole derivatives. We therefore examined their effects on tubulin assembly and colchicine binding. While 3u and 3z did not appear to target tubulin, good activity was observed with 3d and 3p.Molecular docking and molecular dynamics simulations allowed us to rationalize the binding mode of the synthesized compounds toward tubulin. All ligands exhibited a better affinity for the colchicine site, confirming their specificity for this binding pocket. In particular, a better affinity and free energy of binding was observed for 3d and 3p. This result was confirmed by experimental data, indicating that, although both 3d and 3p significantly affected tubulin assembly, only 3d showed activity comparable to that of combretastatin A-4, while 3p was about 4-fold less active.Cell cycle analysis showed that compounds 3u and especially 3z induced a block in G2/M, a strong decrease in S phase even at low compound concentrations and apoptosis through the mitochondrial pathway. Thus, the mechanism of action of 3u and 3z remains to be elucidated.Very high selectivity toward cancer cells and low toxicity in human peripheral blood lymphocytes were observed, highlighting the good potential of these agents in cancer therapy and encouraging further exploration of this compound class to obtain new small molecules as effective lymphoma treatments.

Review on Chemistry of Oxazole derivatives: Current to Future Therapeutic Prospective

ABSTRACT Oxazole and its derivatives play a very essential role in the area of medicinal chemistry. Oxazole nucleus is heterocyclic five-membered ring that seemed to be investigated in the advancement of novel compounds which shows favorable biological activities. In the modern medicinal chemistry scaffold of oxazole has been intermittently satisfied as a functional lead molecule. Prominently, enormous oxazole candidates or drugs are developed for the treatment of disease which increases its developmental values as medicinal agents. The five-membered aromatic ring of oxazole has atoms of nitrogen and oxygen. Through diverse non-covalent bonds, these rings quickly engage physiologically with many enzymes and receptors, resulting in a variety of biological actions. This review presents a logical attempt toward the researches and advancement of chemistry and oxazole derivatives’ biological action. The important information presented in this manuscript will work as impetus for new views in the pursuit for rational design of more biologically active and minimum toxic derivatives of oxazoles as medicinal agents.

Molecular docking analysis of oxazole compounds with the heme-binding protein from Porphyromonas gingivalis.

Porphyromonas gingivalis, a peripathogen, has several methods to impede or modify the protective mechanisms of the teeth. Targeting the inhibition of the heme protein will prevent the organism from multiplying and inhibit the virulence mechanism. The literature derived oxazole compounds (1-5) were docked against the protein's active site, and the results show that the selected oxazole derivatives exhibit better interaction compared to clinically proven drugs.

In Silico Design and Experimental Validation of Novel Oxazole Derivatives Against Varicella zoster virus.

Varicella zoster virus (VZV) infection causes severe disease such as chickenpox, shingles, and postherpetic neuralgia, often leading to disability. Reactivation of latent VZV is associated with a decrease in specific cellular immunity in the elderly and in patients with immunodeficiency. However, due to the limited efficacy of existing therapy and the emergence of antiviral resistance, it has become necessary to develop new and effective antiviral drugs for the treatment of diseases caused by VZV, particularly in the setting of opportunistic infections. The goal of this work is to identify potent oxazole derivatives as anti-VZV agents by machine learning, followed by their synthesis and experimental validation. Predictive QSAR models were developed using the Online Chemical Modeling Environment (OCHEM). Data on compounds exhibiting antiviral activity were collected from the ChEMBL and uploaded in the OCHEM database. The predictive ability of the models was tested by cross-validation, giving coefficient of determination q2 = 0.87-0.9. The validation of the models using an external test set proves that the models can be used to predict the antiviral activity of newly designed and known compounds with reasonable accuracy within the applicability domain (q2 = 0.83-0.84). The models were applied to screen a virtual chemical library with expected activity of compounds against VZV. The 7 most promising oxazole derivatives were identified, synthesized, and tested. Two of them showed activity against the VZV Ellen strain upon primary in vitro antiviral screening. The synthesized compounds may represent an interesting starting point for further development of the oxazole derivatives against VZV. The developed models are available online at OCHEM http://ochem.eu/article/145978 and can be used to virtually screen for potential compounds with anti-VZV activity.

Synthesis, Characterization, and Anti-inflammatory activity of Some Novel Oxazole Derivatives

A series of novel oxazole derivatives (A, A1, A2) were synthesized starting from acetone and urea. The compound (A) was obtained by heating it with acetophenone and urea in iodine. Compound (A) on treatment with 4-amino benzaldehyde (Z)-N-(4-amino benzylidine)-4-((E)-Penta-2, 4-diene-2) oxazole-2-amine afforded (A1). Acylation of compound (A) with 4-amino benzoyl chloride to obtain the corresponding N-(4 phenyl oxazole-2- yl)- benzamide (A2). The structures of compounds have been established employing FTIR and 1H-NMR spectral analysis. All oxazole derivatives were evaluated for anti-inflammatory activity by the carrageenan-induced Rat hind paw method. Derivative A1 shows maximum anti-inflammatory activity.
 Keywords: Oxazoles, anti-inflammatory, Benzamide, acetophenone, indomethacin.

Evaluation of dual potentiality of 2,4,5-trisubstituted oxazole derivatives as aquaporin-4 inhibitors and anti-inflammatory agents in lung cells.

Inflammation is a multifaceted "second-line" adaptive defense mechanism triggered by exo/endogenous threating stimuli and inter-communicated by various inflammatory key players. Unresolved or dysregulated inflammation in lungs results in manifestation of diseases and leads to irreparable damage. Aquaporins (AQPs) are a ubiquitously expressed superfamily of intrinsic transmembrane water channel proteins that modulate the fluid homeostasis. In addition to their conventional functions, AQPs have clinical relevance to inflammation prevailing under the infectious conditions of various lung diseases and this proclaims them as appropriate biomarkers to be targeted. Hence an endeavor was undertaken to identify potential ligands to target AQP4 for the treatment of lung diseases. Oxazole being a versatile bio-potent core, a series of 2,4,5-trisubstituted oxazoles 3a-j were synthesized by a Lewis acid mediated reaction of aroylmethylidene malonates with nitriles. In silico studies conducted using the protein data bank (PDB) structure 3gd8 for AQP4 revealed that compound 3a would serve as a suitable candidate to inhibit AQP4 in human lung cells (NCI-H460). Further, in vitro studies demonstrated that compound 3a could effectively inhibit AQP4 and inflammatory cytokines in lung cells and hence it may be considered as a viable drug candidate for the treatment of various lung diseases.

Sequential annulation and isomerisation reaction of 3-acylmethylidene oxindoles with Huisgen zwitterions and synthesis of 5-(3-oxindolyl)oxazoles.

Herein, we report a facile synthesis of 5-(3-oxindolyl)oxazole derivatives via a sequential annulation and isomerisation reaction of 3-acylmethylidene oxindoles with in situ generated Huisgen zwitterions (HZs) from PPh3 and azodicarboxylates. This reaction exhibits good functional group tolerance with 30 examples of structurally diverse products prepared with moderate to good efficiencies (up to 88% yield), thus providing a generally applicable route to the biologically important 5-(3-indolyl)oxazole structural motifs. Key to the success of this sequential one-pot strategy is the utilization of DBU as a base to promote the isomerisation process of the corresponding intermediate annulation products.

Dicationic copper(I) complexes bearing ENE (E = S, Se) pincer ligands; catalytic applications in regioselective cyclization of 1,6-diynes.

Two novel dicationic binuclear Cu(I) complexes of the type [{(BPPP)E2}Cu]2[BF4]2 (E = S (3a); Se (3b)) bearing (BPPP)E2 (BPPP = bis(diphenylphosphino)pyridine) pincer systems were isolated, and structurally characterized. The solid-state structures of 3a/3b display the presence of intermolecular cuprophilic (Cu⋯Cu) interactions between the two monocationic species, and consist of weak Cu⋯S bonding between the two cations. Besides, complex 3a was introduced as a molecular copper(I) catalyst in cyclization reactions, and new protocols were developed for the synthesis of a series of new oxazole and triazole derivatives bearing alkyne-phenyl propargylic ether substituents. 3a was also found to be active in achieving these two classes of heterocyclic compounds by the mechanical grinding method. One of the key intermediate copper-azide species was detected by the high-resolution mass spectrometry technique, which supports the proposed catalytic pathway. All the reported transformations were accomplished sustainably by employing a well-defined, earth-abundant, and cheap copper(I) catalytic system.

IPr*Oxa - a new class of sterically-hindered, wingtip-flexible N,C-chelating oxazole-donor N-heterocyclic carbene ligands.

N-heterocyclic carbenes (NHCs) have emerged as a major direction in ancillary ligand development for stabilization of reactive metal centers in inorganic and organometallic chemistry. In particular, wingtip-flexible NHCs have attracted significant attention due to their unique ability to provide a sterically-demanding environment for transition metals in various oxidation states. Herein, we report a new class of sterically-hindered, wingtip-flexible NHC ligands that feature N,C-chelating oxazole donors. These ligands are readily accessible through a modular arylation of oxazole derivatives. We report their synthesis and complete structural and electronic characterization. The evaluation of steric, electron-donating and π-accepting properties and coordination chemistry to Ag(I), Pd(II) and Rh(I) is described. Preliminary studies of catalytic activity in Ag, Pd and Rh-catalyzed coupling and hydrosilylation reactions are presented. This study establishes the fluxional behavior of a freely-rotatable oxazole unit, wherein the oxazolyl ring adjusts to the steric and electronic environment of the metal center. Considering the tremendous impact of sterically-hindered NHCs and their potential to stabilize reactive metals by N-chelation, we expect that this class of NHC ligands will be of broad interest in inorganic and organometallic chemistry.