Taking advantage of the interaction between the sulfoxide and heme cofactor to develop indoleamine 2, 3-dioxygenase 1 inhibitors.

Taking advantage of key interactions between sulfoxide and heme cofactor, we used the sulfoxide as the anchor functional group to develop two series of indoleamine 2, 3-dioxygenase 1 (IDO1) inhibitors: 2-benzylsulfinylbenzoxazoles (series 1) and 2-phenylsulfinylbenzoxazoles (series 2). In vitro enzymatic screening shows that both series can inhibit the activity of IDO1 in low micromolar (series 1) or nanomolar (series 2) levels. They also show inhibitory selectivity between IDO1 and tryptophan 2, 3-dioxygenase 2. Interestingly, although series 1 is less potent IDO1 inhibitors of these two series, it exhibited stronger inhibitory activity toward kynurenine production in interferon-γ stimulated BxPC-3 cells. Enzyme kinetics and binding studies demonstrated that 2-sulfinylbenzoxazoles are non-competitive inhibitors of tryptophan, and they interact with the ferrous form of heme. These results demonstrated 2-sulfinylbenzoxazoles as type II IDO1 inhibitors. Furthermore, molecular docking studies supports the sulfoxide being of the key functional group that interacts with the heme cofactor. Compound 22 (series 1) can inhibit NO production in a concentration dependent manner in lipopolysaccharides (LPS) stimulated RAW264.7 cells, and can relieve pulmonary edema and lung injury in LPS induced mouse acute lung injury models.

Discovery of 6-Acylamino/Sulfonamido Benzoxazolone with IL-6 Inhibitory Activity as Promising Therapeutic Agents for Ulcerative Colitis.

Ulcerative colitis has been widely concerned for its persistent upward trend, and the sustained overproduction of pro-inflammatory cytokines such as IL-6 remains a crucial factor in the development of UC. Therefore, the identification of new effective drugs to block inflammatory responses is an urgent and viable therapeutic strategy for UC. In our research, twenty-three 6-acylamino/sulfonamido benzoxazolone derivatives were synthesized, characterized, and evaluated for anti-inflammatory activity against NO and IL-6 production in LPS-induced RAW264.7 cells. The results demonstrated that most of the target compounds were capable of reducing the overexpression of NO and IL-6 to a certain degree. For the most active compounds 3i, 3j and 3 l, the inhibitory activities were superior or equivalent to those of the positive drug celecoxib with a dose-dependent relationship. Furthermore, animal experiments revealed that active derivatives 3i, 3j and 3 l exhibited definitive therapeutical effect on DSS induced ulcerative colitis in mice by mitigating weight loss and DAI score while decreasing levels of pro-inflammatory cytokines such as IL-6 and IFN-γ, simultaneously increasing production of anti-inflammatory cytokines IL-10. In addition, compounds 3i, 3j and 3 l could also inhibit the oxidative stress to alleviate ulcerative colitis by decreasing MDA and MPO levels. These finding demonstrated that compounds 3i, 3j and 3 l hold significant potential as novel therapeutic agents for ulcerative colitis.

Research Progress of Benzothiazole and Benzoxazole Derivatives in the Discovery of Agricultural Chemicals.

Benzoxazole and benzothiazole have a broad spectrum of agricultural biological activities, such as antibacterial, antiviral, and herbicidal activities, which are important fused heterocyclic scaffold structures in agrochemical discovery. In recent years, great progress has been made in the research of benzoxazoles and benzothiazoles, especially in the development of herbicides and insecticides. With the widespread use of benzoxazoles and benzothiazoles, there may be more new products containing benzoxazoles and benzothiazoles in the future. We systematically reviewed the application of benzoxazoles and benzothiazoles in discovering new agrochemicals in the past two decades and summarized the antibacterial, fungicidal, antiviral, herbicidal, and insecticidal activities of the active compounds. We also discussed the structural-activity relationship and mechanism of the active compounds. This work aims to provide inspiration and ideas for the discovery of new agrochemicals based on benzoxazole and benzothiazole.

Synthesis and biological profile of benzoxazolone derivatives.

The benzoxazolone nucleus is an ideal scaffold for drug design, owing to its discrete physicochemical profile, bioisosteric preference over pharmacokinetically weaker moieties, weakly acidic behavior, presence of both lipophilic and hydrophilic fragments on a single framework, and a wider choice of chemical modification on the benzene and oxazolone rings. These properties apparently influence the interactions of benzoxazolone-based derivatives with their respective biological targets. Hence, the benzoxazolone ring is implicated in the synthesis and development of pharmaceuticals with a diverse biological profile ranging from anticancer, analgesics, insecticides, anti-inflammatory, and neuroprotective agents. This has further led to the commercialization of several benzoxazolone-based molecules and a few others under clinical trials. Nevertheless, the SAR exploration of benzoxazolone derivatives for the identification of potential "hits" followed by the screening of "leads" provides a plethora of opportunities for further exploration of the pharmacological profile of the benzoxazolone nucleus. In this review, we aim to present the biological profile of different derivatives based on the benzoxazolone framework.

Synthesis and Anti-Inflammatory Activity Evaluation of Benzoxazole Derivatives as New Myeloid Differentiation Protein 2 Inhibitors.

Myeloid differentiation protein 2 (MD2), a key TLR4 adaptor protein for sensing LPS, plays an important role in inflammatory process and has been identified as a promising target for the treatment of a variety of inflammatory diseases. In our study, a series of benzoxazolone derivatives were synthesized, characterized and tested for anti-inflammatory activity in vitro. The compounds 3c, 3d and 3g demonstrated the greatest anti-inflammatory activity against IL-6 with IC50 values of 10.14±0.08, 5.43±0.51 and 5.09±0.88 µM, respectively. Furthermore, the bis-ANS displacement assay revealed that these compounds competitively inhibited the binding between the probe bis-ANS and the MD2 protein. The most active compound 3g, revealed a directly bind with MD2 protein via Arg90 binding and a dissociation constant value of 1.52×10-6  mol L-1 as determined by the biological layer interference (BLI) assay. Our finding suggested that compounds 3g could be a promising lead compound as MD2 inhibitor for further anti-inflammatory agent development.

Degradation and chiral properties of metamifop during rice processing.

Metamifop has been used to control gramineous weeds in paddy fields and may form residues in rice. In this study, the residue analysis method for metamifop and the metabolites was set up based on high-performance liquid chromatography-mass spectrometry and the chiral analysis method was also developed. The enantioselective degradation and residue of metamifop in rice processing were studied, and the major metabolites were monitored. The removal rate of metamifop by washing could reach 60.03%, while the loss in rice and porridge cooking was less than 16%. No decrease was found in fermentation into fermented grains, but metamifop was degraded in the process of rice wine fermentation with half-lives of around 9.5 days. N-(2-fluorophenyl)-2-(4-hydroxyphenoxy)-N-methylpropionamide and 6-chlorobenzo [d] oxazole-2 (3H)-one were found to be the major metabolites. This study reveals the enantioselective residue of metamifop in rice processing, which helps understand the potential risk in food consumption.

Effect of Flow Rate and Ionic Strength on the Stabilities of YOYO-1 and YO-PRO-1 Intercalated in DNA Molecules.

Single-molecule DNA studies have improved our understanding of the DNAs' structure and their interactions with other molecules. A variety of DNA labeling dyes are available for single-molecule studies, among which the bis-intercalating dye YOYO-1 and mono-intercalating dye YO-PRO-1 are widely used. They have an extraordinarily strong affinity toward DNA and are bright with a high quantum yield (>0.5) when bound to DNAs. However, it is still not clear how these dyes behave in DNA molecules under higher ionic strength and strong buffer flow. Here, we have studied the effect of ionic strength and flow rate of buffer on their binding in single DNA molecules. The larger the flow rate and the higher the ionic strength, the faster the intercalated dyes are washed away from the DNAs. In the buffer with 1 M ionic strength, YOYO-1 and YO-PRO-1 are mostly washed away from DNA within 2 min of moderate buffer flow.

Insights into the Transport Cycle of LAT1 and Interaction with the Inhibitor JPH203.

The large Amino Acid Transporter 1 (LAT1) is an interesting target in drug discovery since this transporter is overexpressed in several human cancers. Furthermore, due to its location in the blood-brain barrier (BBB), LAT1 is interesting for delivering pro-drugs to the brain. In this work, we focused on defining the transport cycle of LAT1 using an in silico approach. So far, studies of the interaction of LAT1 with substrates and inhibitors have not considered that the transporter must undergo at least four different conformations to complete the transport cycle. We built outward-open and inward-occluded conformations of LAT1 using an optimized homology modelling procedure. We used these 3D models and the cryo-EM structures in outward-occluded and inward-open conformations to define the substrate/protein interaction during the transport cycle. We found that the binding scores for the substrate depend on the conformation, with the occluded states as the crucial steps affecting the substrate affinity. Finally, we analyzed the interaction of JPH203, a high-affinity inhibitor of LAT1. The results indicate that conformational states must be considered for in silico analyses and early-stage drug discovery. The two built models, together with the available cryo-EM 3D structures, provide important information on the LAT1 transport cycle, which could be used to speed up the identification of potential inhibitors through in silico screening.

Benzoxazole-appended piperidine derivatives as novel anticancer candidates against breast cancer.

Novel series of benzoxazole-appended piperidine derivatives were planned, synthesized and screened against two breast cancer cell lines. Considerable antiproliferative activity was observed for screened compounds (IC50 = 33.32 ± 0.2 µM to 7.31 ± 0.43 µM and 1.66 ± 0.08 µM to 12.10 ± 0.57 µM) against MCF-7 and MDA-MB-231 cell lines respectively being more potent than doxorubicin (IC50 = 8.20 ± 0.39 µM and 13.34 ± 0.63 µM respectively). Active compounds were submitted for enzyme inhibition assays when 4d and 7h demonstrated potent EGFR inhibition (0.08 ± 0.002 µM and 0.09 ± 0.002 µM respectively) compared to erlotinib (0.11 ± 0.003 µM). However, no one compound displayed effective ARO inhibition activity as tested compounds were less active than letrozole. Apoptosis inducing ability results implied that apoptosis was provoked by significant stimulation of caspase-9 protein levels (4.25-7.04-fold) upon treatment of MCF-7 cells with 4a, 7h, 9, 12e and 12f. Alternatively, MDA-MB-231 cells treated with 4d, 7a, 12b and 12c considerably increased caspase-9 levels (2.32-4.06-fold). Cell cycle arrest and annexin-V/Propidium iodide assays further confirmed apoptosis when tested compounds arrested cell cycle at various phases and demonstrated high annexin V binding affinity. Docking outcomes proved valuable binding affinities for compounds 4d and 7h to EGFR enzyme while compounds 4a and 12e, upon docking into the active site of ARO, failed to interact with heme, suggesting their inabilities to act as AIs. Therefore, these benzoxazoles can act as promising candidates exhibiting EGFR inhibition and apoptosis-promoting properties.

Indole Derivatives Bearing Imidazole, Benzothiazole-2-Thione or Benzoxazole-2-Thione Moieties-Synthesis, Structure and Evaluation of Their Cytoprotective, Antioxidant, Antibacterial and Fungicidal Activities.

In the search for new bioactive compounds, a methodology based on combining two molecules with biological properties into a new hybrid molecule was used to design and synthesize of a series of ten indole derivatives bearing imidazole, benzothiazole-2-thione, or benzoxazole-2-thione moieties at the C-3 position. The compounds were spectroscopically characterized and tested for their antioxidant, antibacterial, and fungicidal activities. The crystal structures were determined for five of them. Comparison of the closely related structures containing either benzothiazole-2-thione or benzoxazole-2-thione clearly shows that the replacement of -S- and -O- ring atoms modify molecular conformation in the crystal, changes intermolecular interactions, and has a severe impact on biological activity. The results indicate that indole-imidazole derivatives with alkyl substituent exhibit an excellent cytoprotective effect against AAPH-induced oxidative hemolysis and act as effective ferrous ion chelating agents. The indole-imidazole compound with chlorine atoms inhibited the growth of fungal strains: Coriolus versicolor (Cv), Poria placenta (Pp), Coniophora puteana (Cp), and Gloeophyllum trabeum (Gt). The indole-imidazole derivatives showed the highest antibacterial activity, for which the largest growth-inhibition zones were noted in M. luteus and P. fluorescens cultures. The obtained results may be helpful in the development of selective indole derivatives as effective antioxidants and/or antimicrobial agents.

Myxococcus xanthus as Host for the Production of Benzoxazoles.

Benzoxazoles are important structural motifs in pharmaceutical drugs. Here, we present the heterologous production of 3-hydroxyanthranilate-derived benzoxazoles in the host bacterium Myxococcus xanthus following the expression of two genes from the nataxazole biosynthetic gene cluster of Streptomyces sp. Tü 6176. The M. xanthus expression strain achieved a benzoxazole titer of 114.6±7.4 mg L-1 upon precursor supplementation, which is superior to other bacterial production systems. Crosstalk between the heterologously expressed benzoxazole pathway and the endogenous myxochelin pathway led to the combinatorial biosynthesis of benzoxazoles featuring a 2,3-dihydroxybenzoic acid (2,3-DHBA) building block. Subsequent in vitro studies confirmed that this crosstalk is not only due to the availability of 2,3-DHBA in M. xanthus, rather, it is promoted by the adenylating enzyme MxcE from the myxochelin pathway, which contributes to the activation of aryl carboxylic acids and delivers them to benzoxazole biosynthesis.

Optimization and SAR research at the benzoxazole and tetrazole rings of JNJ4796 as new anti-influenza A virus agents, part 2.

We have already reported the modification on the piperazine and phenyl rings of JNJ4796, a small-molecule fuse inhibitor targeting hemagglutinin (HA). In this study, we described the structure-activity relationship of the benzoxazole and tetrazole rings of JNJ4796. Many derivatives demonstrated good in vitro activity against IAV H1N1and Oseltamivir-resistant IAV H1N1 stains. Although compounds (R)-1e and (R)-1h exhibited excellent in vitro activity, high drug exposure level and low hERG inhibition, they displayed low oral efficacy. Excitedly, (R)-1a, a representative identified in our previous study, was found to show potent in vivo anti-IAV activity with the survival rates of 100%, 100% and 70% at 15, 5 and 1.67 mg/kg, respectively, comparable to JNJ4796. Currently, we are exploring different ways to ease its gastrointestinal response.

Design, Synthesis, and Anti-Fungal Evaluation of Heterocyclic Benzoxazole Derivatives.

In order to discover more promising anti-fungal agents, a series of benzoxazole family was synthesized by PPA-catalyzed condensation and a Raney nickel/hydrazine reduction. Altogether 45 compounds were obtained in good to excellent yields and characterized by FT-IR, NMR, MS, and X-ray crystal diffraction. Moreover, the biological activity against eight phytopathogenic fungi was investigated. All in all, most of these compounds bear moderate antifungal activities. Among them, three candidates show the strongest activities, compound 4ac, 4bc provided over 50% inhibition rate against five fungi. Especially, the inhibitory rate of compound 4ah on Mycosphaerella melonis reached 76.4%.

Spectroscopic and mechanistic insights into solvent mediated excited-state proton transfer and aggregation-induced emission: introduction of methyl group onto 2-(o-hydroxyphenyl)benzoxazole.

Excited-state intramolecular proton transfer (ESIPT) reaction plays an important role in biology, materials, and other related fields. The ESIPT-based compounds has been proved to improve effectively fluorescence quantum yield, red-shifted emission, and wide separation between absorption and emission wavelengths (large Stokes shift, LSS). A solvatochromic benzoxazole-based probe, 2-(2-hydroxy-5-methylphenyl)benzoxazole(HBO-pCH3), exhibited a typical dual fluorescence phenomenon via the ESIPT reaction in non-polar and weakly polar solvents. The emission bands of normal* (∼370 nm) and tautomer* (∼500 nm) forms were identified and assigned, based on fluorescence spectroscopy and quantum chemical theoretical calculations. Solvatochromism confirmed ESIPT reaction inhibition by solvent polarity and intermolecular hydrogen bonding. The intramolecular reversal in combination with time-dependent density functional theoretical calculations revealed an emission-strengthening mechanism of ESIPT, coupled with aggregation-induced emission (AIE) (in mixed water/methanol solvents). Thus, this strategy provides an insight into designing potential "ESIPT + AIE" fluorescent sensors.

Synthesis and Biological Evaluation of 2-(Halophenyl)benzoxazole-5-Carboxylic Acids as Potential Anti-Inflammatory and Cytotoxic Agent with Molecular Docking Studies.

2-Halogenatedphenyl benzoxazole-5-carboxylic acids with mono-halogen (chloro, bromo and fluoro) substituted at ortho-, meta- and para-positions on the phenyl ring were designed and synthesized based on significance of presence of halogen in increasing number of marketed halogenated drugs and importance of benzoxazoles. These 2-alogenatedphenylbenzoxazole-5-carboxylic acids and their methyl esters were screened for anti-inflammatory activity, and cytotoxicity. 2-(3-Chlorophenyl)benzoxaole-5-carboxylic acid (6b) exhibited significant anti-inflammatory activity with IC50 values of 0.103 mM almost equivalent to the standard drug ibuprofen (0.101 mM). 2-(4-Chlorophenyl)benzoxaole-5-carboxylic acid (6c) showed excellent cytotoxic activity against 22Rv1 cells (human prostate carcinoma epithelial cell lines) with IC50 value of 1.54 µM better than that of standard drug doxorubicin having IC50 value of 2.32 µM. More importantly, the selectivity index of this potential molecule was found to be 57.74. Molecular docking analysis resulted in good binding interactions of these compounds with their respective biochemical targets viz. Cyclooxygenase-2 and aldo-keto reductase IC3.

Synthesis, biological evaluation, and molecular modeling studies of new benzoxazole derivatives as PARP-2 inhibitors targeting breast cancer.

Many benzoxazole-based and similar scaffolds were reported to have wide-range of anticancer activities. In this study, four series of benzoxazole derivatives were designed by combining benzoxazole scaffold with different amines via a reversed phenyl amide linker to produce the compounds of series A, B and C. A fourth new hybrid of benzoxazole with 1,2,3 triazole ring (series D) was also designed. The designed compounds were synthesized and screened for their anti-breast cancer activity against MDA-MB-231 and MCF-7 cell lines using MTT assay. The most potent cytotoxic compounds; 11-14, 21, 22, 25-27 were further evaluated for their in vitro PARP-2 enzyme inhibition. Compounds 12 and 27 proved to be the most active PARP-2 inhibitors with IC50 values of 0.07 and 0.057 µM, respectively. Compounds 12 and 27 caused cell cycle arrest in mutant MCF-7 cell line at G2/M and G1/S phase, respectively and they possessed significant apoptosis-promoting activity. Docking results of compounds 12 and 27 into PARP-2 pocket demonstrated binding interactions comparable to those of olaparib. Their predicted pharmacokinetic parameters and oral bioavailability appeared to be appropriate. Collectively, it could be concluded that compounds 12 and 27 are promising anti-breast cancer agents that act as PARP-2 inhibitors with potent apoptotic activity.

Modified Benzoxazole-Based VEGFR-2 Inhibitors and Apoptosis Inducers: Design, Synthesis, and Anti-Proliferative Evaluation.

This work is one of our efforts to discover potent anticancer agents. We modified the most promising derivative of our previous work concerned with the development of VEGFR-2 inhibitor candidates. Thirteen new compounds based on benzoxazole moiety were synthesized and evaluated against three human cancer cell lines, namely, breast cancer (MCF-7), colorectal carcinoma (HCT116), and hepatocellular carcinoma (HepG2). The synthesized compounds were also evaluated against VEGFR-2 kinase activity. The biological testing fallouts showed that compound 8d was more potent than standard sorafenib. Such compound showed IC50 values of 3.43, 2.79, and 2.43 µM against the aforementioned cancer cell lines, respectively, compared to IC50 values of 4.21, 5.30, and 3.40 µM reported for sorafenib. Compound 8d also was found to exert exceptional VEGFR-2 inhibition activity with an IC50 value of 0.0554 µM compared to sorafenib (0.0782 µM). In addition, compound 8h revealed excellent cytotoxic effects with IC50 values of 3.53, 2.94, and 2.76 µM against experienced cell lines, respectively. Furthermore, compounds 8a and 8e were found to inhibit VEGFR-2 kinase activity with IC50 values of 0.0579 and 0.0741 µM, exceeding that of sorafenib. Compound 8d showed a significant apoptotic effect and arrested the HepG2 cells at the pre-G1 phase. In addition, it exerted a significant inhibition for TNF-α (90.54%) and of IL-6 (92.19%) compared to dexamethasone (93.15%). The molecular docking studies showed that the binding pattern of the new compounds to VEGFR-2 kinase was similar to that of sorafenib.

Electrosynthesis of 2-Substituted Benzoxazoles via Intramolecular Shono-Type Oxidative Coupling of Glycine Derivatives.

Herein, an atom-economical and eco-friendly electrochemical oxidation/cyclization of glycine derivatives through intramolecular Shono-type oxidative coupling is disclosed, leading to a variety of 2-substituted benzoxazoles in 51-85% yields. This oxidative cyclization proceeded in transition metal- and oxidant-free conditions and generated H2 as only a byproduct. Additionally, gram-scale reactions and a broad substrate scope demonstrated the synthetic usefulness of this protocol.

Alternative Benzoxazole Assembly Discovered in Anaerobic Bacteria Provides Access to Privileged Heterocyclic Scaffold.

Benzoxazole scaffolds feature prominently in diverse synthetic and natural product-derived pharmaceuticals. Our understanding of their bacterial biosynthesis is, however, limited to ortho-substituted heterocycles from actinomycetes. We report an overlooked biosynthetic pathway in anaerobic bacteria (typified in Clostridium cavendishii) that expands the benzoxazole chemical space to meta-substituted heterocycles and heralds a distribution beyond Actinobacteria. The first benzoxazoles from the anaerobic realm (closoxazole A and B) were elucidated by NMR and chemical synthesis. By genome editing in the native producer, heterologous expression in Escherichia coli, and systematic pathway dissection we show that closoxazole biosynthesis invokes an unprecedented precursor usage (3-amino-4-hydroxybenzoate) and manner of assembly. Synthetic utility was demonstrated by the precursor-directed biosynthesis of a tafamidis analogue. A bioinformatic survey reveals the pervasiveness of related gene clusters in diverse bacterial phyla.

Molecular-docking-guided design, palladium-catalyzed synthesis and anticancer activity of paclitaxel-benzoxazoles hybrids.

A series of new paclitaxel-benzoxazoles hybrids were designed based on both the molecular docking mode of beta-tubulin with paclitaxel derivatives (7a and 7g), and the activity-structure relationship of C-13 side chain in paclitaxel. Palladium-catalyzed direct Csp2-H arylation of benzoxazoles with different aryl-bromides was used as the key synthetic strategy for the aryl-benzoxazoles moieties in the hybrids. Twenty-six newly synthesized hybrids were screened for their antiproliferative activity against human cancer cell lines such as human breast cancer cells (MDA-MB-231) and liver hepatocellular cells (HepG2) by the MTT assay and results were compared with paclitaxel. Interestingly, most hybrids (7a-7e, 7i, 7k, 7l, 7A, 7B, 7D and 7E) showed significantly active against both cell lines at concentration of 50 µM, which indicated that the hybrid strategy is effective to get structural simplified paclitaxel analogues with high anti-tumor activity.