Substrate-based synthetic strategies and biological activities of 1,3,4-oxadiazole: A review.

The five-membered 1,3,4-oxadiazole heterocyclic ring has received considerable attention because of its unique bio-isosteric properties and an unusually wide spectrum of biological activities. After a century since 1,3,4-oxadiazole was discovered, its uncommon potential attracted medicinal chemist's attention, leading to the discovery of a few presently accessible drugs containing 1,3,4-oxadiazole units, and a large number of patents have been granted on research related to 1,3,4-oxadiazole. It is worth noting that interest in 1,3,4-oxadiazoles' biological applications has doubled in the last few years. Herein, this review presents a comprehensive overview of the recent achievements in the synthesis of 1,3,4-oxadiazole-based compounds and highlights the major advances in their biological applications in the last 10 years, as well as brief remarks on prospects for further development. We hope that researchers across the scientific streams will benefit from the presented review articles for designing their work related to 1,3,4-oxadiazoles.

New benzimidazole-oxadiazole derivatives as potent VEGFR-2 inhibitors: Synthesis, anticancer evaluation, and docking study.

We report herein, the design and synthesis of benzimidazole-oxadiazole derivatives as new inhibitors for vascular endothelial growth factor receptor-2 (VEGFR-2). The designed members were assessed for their in vitro anticancer activity against three cancer cell lines and two normal cell lines; A549, MCF-7, PANC-1, hTERT-HPNE and CCD-19Lu. Compounds 4c and 4d were found to be the most effective compounds against three cancer cell lines. Compounds 4c and 4d were then tested for their in vitro VEGFR-2 inhibitory activity, safety profiles, and selectivity indices using the normal hTERT-HPNE and CCD-19Lu cell lines. It was determined that compound 4c was the most effective and safe member of the produced chemical family. Vascular endothelial growth factor A (VEGFA) immunolocalizations of compounds 4c and 4d were evaluated relative to control by VEGFA immunofluorescence staining. Compounds 4c and 4d inhibited VEGFR-2 enzyme with half-maximal inhibitory concentration values of 0.475 ± 0.021 and 0.618 ± 0.028 µM, respectively. Molecular docking of the target compounds was carried out in the active site of VEGFR-2 (Protein Data Bank: 4ASD).

Discovery of 1,3,4-Oxadiazole Derivatives as Broad-Spectrum Antiparasitic Agents.

Vector-borne parasitic diseases (VBPDs) pose a significant threat to public health on a global scale. Collectively, Human African Trypanosomiasis (HAT), Leishmaniasis, and Malaria threaten millions of people, particularly in developing countries. Climate change might alter the transmission and spread of VBPDs, leading to a global burden of these diseases. Thus, novel agents are urgently needed to expand therapeutic options and limit the spread of drug-resistant parasites. Herein, we report the development of broad-spectrum antiparasitic agents by screening a known library of antileishmanial and antimalarial compounds toward Trypanosoma brucei (T. brucei) and identifying a 1,3,4-oxadiazole derivative (19) as anti-T. brucei hit with predicted blood-brain barrier permeability. Subsequently, extensive structure-activity-relationship studies around the lipophilic tail of 19 led to a potent antitrypanosomal and antimalarial compound (27), with moderate potency also toward Leishmania infantum (L. infantum) and Leishmania tropica. In addition, we discovered a pan-active antiparasitic molecule (24), showing low-micromolar IC50s toward T. brucei and Leishmania spp. promastigotes and amastigotes, and nanomolar IC50 against Plasmodium falciparum, together with high selectivity for the parasites over mammalian cells (THP-1). Early ADME-toxicity assays were used to assess the safety profile of the compounds. Overall, we characterized 24 and 27, bearing the 1,3,4-oxadiazole privileged scaffold, as broad-spectrum low-toxicity agents for the treatment of VBPDs. An alkyne-substituted chemical probe (30) was synthesized and will be utilized in proteomics experiments aimed at deconvoluting the mechanism of action in the T. brucei parasite.

[Changing Concepts About Optimal Target Blood Pressure and the Therapeutic Advantages of Azilsartan for Achieving it].

The article discusses current issues of the treatment of arterial hypertension. According to presented data, so-called therapeutic nihilism is becoming one of the main barriers to achieving target blood pressure (BP). This nihilism is that despite evidence of the effectiveness of achieving lower BP values, practitioners do not intensify antihypertensive therapy sufficiently to achieve such values. The article specially addresses new criteria for the effectiveness of antihypertensive therapy, which reflect the therapy sustainability. The most commonly used indicator is the duration of the period, during which systolic BP remains in the therapeutic range. The prognostic significance of such indicators is discussed. In these conditions, it is very important to use the most effective antihypertensive drugs for initial antihypertensive therapy, including as a part of combination therapy. This tactic provides more frequent achievement of BP goals without the need for dose adjustment. In this regard, a systematic review was performed, which included sufficiently large randomized studies of the antihypertensive effectiveness of azilsartan medoxomil. This systematic review will provide comprehensive information on a possible role of using the angiotensin II receptor blocker azilsartan as a basic drug for the treatment of a wide range of patients with high BP. Most of the studies included in the systematic review assessed the effectiveness of combination therapy including azilsartan.

Repairing Host Damage Caused by Tobacco Mosaic Virus Stress: Design, Synthesis, and Mechanism Study of Novel Oxadiazole and Arylhydrazone Derivatives.

Tobacco mosaic virus (TMV), as one of the most traditional and extensive biological stresses, poses a serious threat to plant growth and development. In this work, a series of 1-phenyl/tertbutyl-5-amino-4-pyrazole oxadiazole and arylhydrazone derivatives was synthesized. Bioassay evaluation demonstrated that the title compounds (P1-P18) without a "thioether bond" lost their anti-TMV activity, while some of the ring-opening arylhydrazone compounds exhibited superior in vivo activity against TMV in tobacco. The EC50 value of title compound T8 for curative activity was 139 µg/mL, similar to that of ningnanmycin (NNM) (EC50 = 152 µg/mL). Safety analysis revealed that compound T8 had no adverse effects on plant growth or seed germination at a concentration of 250 µg/mL. Morphological observation revealed that compound T8 could restore the leaf tissue of a TMV-stressed host and the leaf stomatal aperture to normal. A mechanism study further revealed that compound T8 not only restored the photosynthetic and growth ability of the damaged host to normal levels but also enhanced catalase (CAT) activity and reduced the content of malondialdehyde (MDA) and hydrogen peroxide (H2O2) in the damaged host, thereby reducing the oxidation damage to the host. TMV-green fluorescent protein (GFP) experiments further demonstrated that compound T8 not only slowed the transmission speed of TMV in the host but also inhibited its reproduction. All of the experimental results demonstrated that compound T8 could reduce the oxidative damage caused by TMV stress and regulate the photosynthetic ability of the host, achieving the ability to repair damage, to make the plant grow normally.

OFF-times before, during, and after nighttime sleep periods in Parkinson's disease patients with motor fluctuations and the effects of opicapone: A post hoc analysis of diary data from BIPARK-1 and -2.

INTRODUCTION: In BIPARK-1 and BIPARK-2, addition of once-daily opicapone to levodopa/carbidopa significantly reduced daily "OFF"-time relative to placebo in adults with Parkinson's disease (PD) and motor fluctuations. Diary data from these studies were pooled and analyzed post hoc to characterize "OFF"-times around nighttime sleep and to explore the effects of opicapone 50 mg. METHODS: "OFF" before sleep (OBS), "OFF during the nighttime sleep period" (ODNSP), early morning "OFF" (EMO), and duration of nighttime sleep and awake periods were analyzed descriptively at baseline. Mean changes from baseline to Week 14/15 (end of double-blind treatment) were analyzed using two-sided t-tests in participants with data for both visits. RESULTS: At baseline, 88.3 % (454/514) of participants reported having OBS (34.0 %), ODNSP (17.1 %), or EMO (79.6 %). Those with ODNSP had substantially shorter mean duration of uninterrupted sleep (4.4 h) than the overall pooled population (7.1 h). At Week 14/15, mean decrease from baseline in ODNSP duration was significantly greater with opicapone than with placebo (-0.9 vs. -0.4 h, P < 0.05). In participants with ODNSP at baseline, the decrease in total time spent awake during the night-time sleep period was significantly greater with opicapone than with placebo (-1.0 vs. -0.4 h, P < 0.05), as was the reduction in percent time spent awake during the night-time sleep period (-12.8 % vs. -4.5 %, P < 0.05). CONCLUSION: "OFF"-times around nighttime sleep were common in BIPARK-1 and BIPARK-2. Opicapone may improve sleep by decreasing the amount of time spent awake during the night in patients with PD who have night-time sleep period "OFF" episodes.

Bovine carbonic anhydrase (bCA) inhibitors: Synthesis, molecular docking and theoretical studies of bisoxadiazole-substituted sulfonamide derivatives.

This paper describes the in vitro inhibition potential of bisoxadiazole-substituted sulfonamide derivatives (6a-t) against bovine carbonic anhydrase (bCA) after they were designed through computational analyses and evaluated the predicted interaction via molecular docking. First, in silico ADMET predictions and physicochemical property analysis of the compounds provided insights into solubility and permeability, then density functional theory (DFT) calculations were performed to analyse their ionization energies, nucleophilicity, in vitro electron affinity, dipole moments and molecular interactions under vacuum and dimethyl sulfoxide (DMSO) conditions. After calculating the theoretical inhibition constants, IC50 values determined from enzymatic inhibition were found between 12.93 and 45.77 µM. Molecular docking evaluation revealed favorable hydrogen bonding and π-interactions of the compounds within the bCA active site. The experimentally most active compound, 6p, exhibited the strongest inhibitory activity with a theoretical inhibition constant value of 9.41 nM and H-bonds with Gln91, Thr198, and Trp4 residues and His63 Pi-cation interactions with His63 residues. Overall, the study reveals promising bCA blocking potential for the synthesized derivatives, similar to acetazolamide.

Design, synthesis, in silico and biological evaluation of new indole based oxadiazole derivatives targeting estrogen receptor alpha.

A series of new indole-oxadiazole derivatives was designed and synthesized to develop potential anti-breast cancer agents. The compounds exhibited significant inhibitory activity with IC50 values ranging from 1.78 to 19.74 µM against ER-positive human breast cancer (BC) cell lines T-47D and MCF-7. Among them, compounds (5a, 5c, 5e-5h, 5j-5o) displayed superior activity against ER-α dominant (ratio of ER-α/ER-ß is 9/1) T-47D cells compared to the standard drug bazedoxifene (IC50 = 12.78 ± 0.92 µM). Compounds 5c and 5o exhibited remarkable anti-proliferative activity with IC50 values of 3.24 ± 0.46 and 1.72 ± 1.67 µM against T-47D cells, respectively. Further, compound 5o manifested 1589-fold higher ER-α binding affinity (213.4 pM) relative to bazedoxifene (339.2 nM) in a competitive ER-α binding assay, while compound 5c showed a binding affinity of 446.6 nM. The Western blot analysis proved that both compounds influenced the ER-α protein's expression, impeding its subsequent transactivation and signalling pathway within T-47D cells. Additionally, a molecular docking study suggests that compounds 5c and 5o bind in such a fashion that induces conformational changes in the protein, culminating in their antagonistic effect. Also, pharmacokinetic profiles showed that all compounds have drug-like properties. Further, molecular dynamic (MD) simulations and density functional theory (DFT) analysis confirmed the stability, conformational behaviour, reactivity, and biological feasibility of compounds 5c and 5o. In conclusion, based on our findings, compounds 5c and 5o, which exhibit significant ER-α antagonistic activity, can act as potential lead compounds for developing anti-breast cancer agents.

Novel 1,3,4-oxadiazole derivatives as highly potent microsomal prostaglandin E2 synthase-1 (mPGES-1) inhibitors.

Selective inhibition of microsomal prostaglandin E2 synthase-1 (mPGES-1) is implicated as a new therapeutic modality for the development of new-generation anti-inflammatory drugs. Here, we present the discovery of new and potent inhibitors of human mPGES-1, i.e., compounds 13, 15-25, 29-30 with IC50 values in the range of 5.6-82.3 nM in a cell-free assay of prostaglandin (PG)E2 formation. We also demonstrate that 20 (TG554, IC50 = 5.6 nM) suppresses leukotriene (LT) biosynthesis at low µM concentrations, providing a benchmark compound that dually intervenes with inflammatory PGE2 and LT biosynthesis. Comprehensive lipid mediator (LM) metabololipidomics with activated human monocyte-derived macrophages showed that TG554 selectively inhibits inflammatory PGE2 formation over all cyclooxygenase (COX)-derived prostanoids, does not cause substrate shunting towards 5-lipoxygenase (5-LOX) pathway, and does not interfere with the biosynthesis of the specialized pro-resolving mediators as observed with COX inhibitors, providing a new chemotype for effective and safer anti-inflammatory drug development.

A host-directed oxadiazole compound potentiates antituberculosis treatment via zinc poisoning in human macrophages and in a mouse model of infection.

Antituberculosis drugs, mostly developed over 60 years ago, combined with a poorly effective vaccine, have failed to eradicate tuberculosis. More worryingly, multiresistant strains of Mycobacterium tuberculosis (MTB) are constantly emerging. Innovative strategies are thus urgently needed to improve tuberculosis treatment. Recently, host-directed therapy has emerged as a promising strategy to be used in adjunct with existing or future antibiotics, by improving innate immunity or limiting immunopathology. Here, using high-content imaging, we identified novel 1,2,4-oxadiazole-based compounds, which allow human macrophages to control MTB replication. Genome-wide gene expression analysis revealed that these molecules induced zinc remobilization inside cells, resulting in bacterial zinc intoxication. More importantly, we also demonstrated that, upon treatment with these novel compounds, MTB became even more sensitive to antituberculosis drugs, in vitro and in vivo, in a mouse model of tuberculosis. Manipulation of heavy metal homeostasis holds thus great promise to be exploited to develop host-directed therapeutic interventions.

Design, Synthesis, and Biological Evaluation of Eukaryotic Initiation Factor 2B (eIF2B) Activators.

The eukaryotic initiation factor 2B (eIF2B) is a key regulator in protein-regulated signaling pathways and is closely related to the function of the central nervous system. Modulating eIF2B could retard the process of neurodegenerative diseases, including Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), and vanishing white matter disease (VWM) et al. Here, we designed and synthesized a series of novel eIF2B activators containing oxadiazole fragments. The activating effects of compounds on eIF2B were investigated through testing the inhibition of ATF4 expression. Of all the targeted compounds, compounds 21 and 29 exhibited potent inhibition on ATF4 expression with IC50 values of 32.43 nM and 47.71 nM, respectively, which were stronger than that of ISRIB (IC50=67.90 nM). ATF4 mRNA assay showed that these two compounds could restore ATF4 mRNA to normal levels in thapsigargin-stimulated HeLa cells. Protein Translation assay showed that both compounds were effective in restoring protein synthesis. Compound potency assay showed that both compounds had similar potency to ISRIB with EC50 values of 5.844 and 37.70 nM. Cytotoxicity assay revealed that compounds 21 and 29 had low toxicity and were worth further investigation.

Selective Potentiation of the (α4)3(ß2)2 Nicotinic Acetylcholine Receptor Response by NS9283 Analogues.

NS9283, 3-(3-pyridyl)-5-(3-cyanophenyl)-1,2,4-oxadiazole, is a selective positive allosteric modulator of (α4)3(ß2)2 nicotinic acetylcholine receptors (nAChRs). It has good subtype selective therapeutic potential afforded by its specific binding to the unique α4-α4 subunit interface present in the (α4)3(ß2)2 nAChR. However, there is currently a lack of structure activity relationship (SAR) studies aimed at developing a class of congeners endowed with the same profile of activity that can help consolidate the druggability of the α4-α4 subunit interface. In this study, new NS9283 analogues were designed, synthesized, and characterized for their ability to selectively potentiate the ACh activity at heterologous (α4)3(ß2)2 nAChRs vs nAChR subtypes (α4)2(ß2)3, α5α4ß2, and α7. With few exceptions, all the NS9283 analogues exerted positive modulation of the (α4)3(ß2)2 nAChR ACh-evoked responses. Above all, those modified at the 3-cyanophenyl moiety by replacement with 3-nitrophenyl (4), 4-cyanophenyl (10), and N-formyl-4-piperidinyl (20) showed the same efficacy as NS9283, although with lower potency. Molecular dynamics simulations of NS9283 and some selected analogues highlighted consistency between potentiation activity and pose of the ligand inside the α4-α4 site with the main interaction being with the complementary (-) side and induction of a significant conformational change of the Trp156 residue in the principal (+) side.

New oxadiazole and pyrazoline derivatives as anti-proliferative agents targeting EGFR-TK: design, synthesis, biological evaluation and molecular docking study.

Two new series of oxadiazole and pyrazoline derivatives were designed and synthesized as promising EGFR-TK inhibitors. The in vitro antiproliferative activity was studied against three human cancer cell lines; HCT116, HepG-2 and MCF7 using MTT assay. Compound 10c showed the most potent anticancer activity against all cancer cell lines, with IC50 range of 1.82 to 5.55 µM, while proving safe towards normal cells WI-38 (IC50 = 41.17 µM) compared to the reference drug doxorubicin (IC50 = 6.72 µM). The most active candidates 5a, 9b, 10a, 10b and 10c were further assessed for their EGFR-TK inhibition. The best of which, compounds 5a and 10b showed IC50 of 0.09 and 0.16 µM respectively compared to gefitinib (IC50 = 0.04 µM). Further investigation against other EGFR family members, showed that 5a displayed good activities against HER3 and HER4 with IC50 values 0.18 and 0.37 µM, respectively compared to gefitinib (IC50 = 0.35 and 0.58 µM, respectively). Furthermore, 5a was evaluated for cell cycle distribution and apoptotic induction on HepG-2 cells. It induced mitochondrial apoptotic pathway and increased accumulation of ROS. Molecular docking study came in agreement with the biological results. Compounds 5a and 10b showed promising drug-likeness with good physicochemical properties.

Discovery of novel polyheterocyclic neuraminidase inhibitors with 1,3,4-oxadiazole thioetheramide as core backbone.

Inspired by our earlier findings regarding neuraminidase (NA) inhibitors interacting with 150-cavity or 430-cavity of NA, sixteen novel polyheterocyclic NA inhibitors with 1,3,4-oxadiazole thioetheramide as core backbone were designed and synthesized based on the lead compound ZINC13401480. Of the synthesized compounds, compound N5 targeting 150-cavity exerts the best inhibitory activity against the wild-type H5N1 NA, with IC50 value of 0.14 µM, which is superior to oseltamivir carboxylate (OSC) (IC50 = 0.31 µM). Compound N10 targeting 430-cavity exhibits the best activity against the H5N1-H274Y mutant NA. Although the activity of N10 is comparable to that of OSC for wild-type H5N1 inhibition, it is approximately 60-fold more potent than OSC against the H274Y mutant, suggesting that it is not easy for the virus to develop drug resistance and is attractive for drug development. N10 (EC50 = 0.11 µM) also exhibits excellent antiviral activity against H5N1, which is superior to the positive control OSC (EC50 = 1.47 µM). Molecular docking study shows that the occupation of aromatic fused rings and oxadiazole moiety at the active site and the extension of the substituted phenyl to the 150-cavity or 430-cavity make great contributions to the good potency of this series of polyheterocyclic NA inhibitors. Some advancements in the discovery of effective target-specific NA inhibitors in this study may offer some assistance in the development of more potent anti-influenza drugs.

New Alpha9 nAChR Ligands Based on a 5-(Quinuclidin-3-ylmethyl)-1,2,4-oxadiazole Scaffold.

Several lines of evidence have indicated that nicotinic acetylcholine receptors (nAChR) that contain α9 subunits, probably in combination with α10 subunits, may be valuable targets for the management of pain associated with inflammatory diseases through a cholinergic anti-inflammatory system (CAS), which has also been associated with α7 nAChR. Both α7- and α9-containing neuronal nAChR can be pharmacologically distinguished from the high-affinity nicotinic receptors of the brain by their sensitivity to α-bungarotoxin, but in other ways, they have quite distinct pharmacological profiles. The early association of α7 with CAS led to the development of numerous new ligands, variously characterized as α7 agonists, partial agonists, or silent agonists that desensitized α7 receptors without activation. Subsequent reinvestigation of one such family of α7 ligands based on an N,N-diethyl-N'-phenylpiperazine scaffold led to the identification of potent agonists and antagonists for α9. In this paper, we characterize the α9/α10 activity of a series of compounds based on a 5-(quinuclidin-3-ylmethyl)-1,2,4-oxadiazole (QMO) scaffold and identify two new potent ligands of α9, QMO-28, an agonist, and QMO-17, an antagonist. We separated the stereoisomers of these compounds to identify the most potent agonist and discovered that only the 3R isomer of QMO-17 was an α9 antagonist, permitting an in silico model of α9 antagonism to be developed. The α9 activity of these compounds was confirmed to be potentially useful for CAS management of inflammatory pain in cell-based assays of cytokine release.

Stimuli-responsive biotin-anchored prodrug for the targeted delivery of anti-cancer agent NBDHEX with turn-on NIR fluorescence.

Biothiol-activatable prodrug RK-296 was designed for the delivery of potent anti-cancer agent NBDHEX with concomitant turn-on near infrared (NIR) fluorescence. NBDHEX exhibits anti-cancer activity by selectively inhibiting glutathione-S-transferase pi (GSTP1), which is overexpressed in cancer cells and responsible for the inactivation of chemotherapeutic drugs. The sustained release of NBDHEX from the prodrug would be useful for ameliorating the off-target side-effects of NBDHEX.

New daphnane diterpenoidal 1,3,4-oxdiazole derivatives as potential anti-hepatoma agents: Synthesis, biological evaluation and molecular modeling studies.

Hepatocellular carcinoma (HCC) is a major challenge for human healthy. Daphnane-type diterpenes have attracted increasingly attention due to remarkable pharmaceutical potential including anti-HCC activity. To further develop this class of compounds as inhibitors of HCC, the daphnane diterpenoids 12-O-debenzoyl-Yuanhuacine (YHC) and 12-hydroxydaphnetoxin (YHE) were prepared by a standard chemical transformation from dried flower buds of the Daphne genkwa plant. Subsequently, 22 daphnane diterpenoidal 1,3,4-oxdiazole derivatives were rationally designed and synthesized based on YHC and YHE. The assessment of the target compound's anti-hepatocellular carcinoma activity revealed that YHC1 exhibited comparable activity to sorafenib in the Hep3B cell line, while demonstrating higher selectivity. The mechanistic investigation demonstrates that compound YHC1 induces cell cycle arrest at the G0/G1 phase, cellular senescence, apoptosis, and elevates cellular reactive oxygen species levels. Moreover, molecular docking and CETSA results confirm the interaction between YHC1 and YAP1 as well as TEAD1. Co-IP experiments further validated that YHC1 can effectively inhibit the binding of YAP1 and TEAD1. In conclusion, YHC1 selectively targets YAP1 and TEAD1, exhibiting its anti-hepatocellular carcinoma effects through the inhibition of their interaction.

Synthesis and antimicrobial activity of thiophene-based heterocycles derived from thiophene-2-carbohydrazide.

Aim: Thiophene-based heterocycles were synthesized and evaluated for their antimicrobial activity against methicillin-resistant Staphylococcus aureus, Escherichia coli, Clostridium difficile and Candida albicans strains. Methods: Antimicrobial activity was determined using the broth microdilution method. Results: Spiro-indoline-oxadiazole 17 displayed the highest activity against C. difficile while having no effects against other bacterial strains. Compounds 8 and 16 displayed strong effects against TolC, an outer membrane protein, mutant E. coli. The results of computational chemical study and outcomes of experiments were in good agreement. A molecular docking study was conducted using a molecular operating environment to simulate the binding energies of the potent compounds with D-alanine ligase protein. Conclusion: This study suggests that spiro-indoline-oxadiazole 17 could be a good anticlostridial agent.

A series of thiophene-based heterocycles was synthesized and evaluated for their antimicrobial activity against methicillin-resistant Staphylococcus aureus, Escherichia coli, Clostridium difficile and Candida albicans strains. Notablly, a spiro­indoline­oxadiazole derivative displayed the highest activity against C. difficile with minimum inhibitory concentration values of 2 to 4 µg/ml. Interestingly, this compound exhibited no effects against other tested bacterial strains. For C. difficile, drugs that can inhibit it without affecting other Gram-positive or Gram-negative bacteria (not affecting the normal microbiota) are needed. This compound could be a good anticlostridial agent.

Design, Synthesis, and Target Identification of Novel Phenylalanine Derivatives by Drug Affinity Responsive Target Stability (DARTS) in Xanthomonas oryzae pv Oryzae.

The increasing resistance displayed by plant phytopathogenic bacteria to conventional pesticides has heightened the urgency for the exploration of novel antibacterial agents possessing distinct modes of action (MOAs). In this study, a series of novel phenylalanine derivatives with the unique structure of acylhydrazone dithioether have been designed and synthesized. Bioassay results demonstrated that most target compounds exhibited excellent in vitro antibacterial activity against Xanthomonas oryzae pv oryzae (Xoo) and Xanthomonas axonopodis pv citri (Xac). Among them, the EC50 values of L3, L4, L6, L21, and L22 against Xoo were 7.4, 9.3, 6.7, 8.9, and 5.1 µg/mL, respectively, superior to that of bismerthiazol (BT) and thiodiazole copper (TC) (41.5 and >100 µg/mL); the EC50 values of L3, L4, L5, L6, L7, L8, L20, L21, and L22 against Xac were 5.6, 2.5, 6.2, 4.1, 4.2, 6.4, 6.3, 3.6, and 5.2 µg/mL, respectively, superior to that of BT and TC (43.3 and >100 µg/mL). An unmodified drug affinity responsive target stability (DARTS) technology was used to investigate the antibacterial MOAs of active compound L22, and the 50S ribosomal protein L2 (RL2) as an unprecedented target protein in Xoo cells was first discovered. The target protein RL2 was then expressed and purified. Furthermore, the in vitro interactions by microscale thermophoresis (Kd = 0.050 µM) and fluorescence titration (Ka = 1.4 × 105 M-1) experiments also demonstrated a strong binding force between compound L22 and RL2. Overall, these results not only facilitate the development of novel antibacterial agents but also establish a reliable method for exploring the targets of bactericides.

Discovery of dual-active ethionamide boosters inhibiting the Mycobacterium tuberculosis ESX-1 secretion system.

Drug-resistant Mycobacterium tuberculosis (Mtb) remains a major public health concern requiring complementary approaches to standard anti-tuberculous regimens. Anti-virulence molecules or compounds that enhance the activity of antimicrobial prodrugs are promising alternatives to conventional antibiotics. Exploiting host cell-based drug discovery, we identified an oxadiazole compound (S3) that blocks the ESX-1 secretion system, a major virulence factor of Mtb. S3-treated mycobacteria showed impaired intracellular growth and a reduced ability to lyse macrophages. RNA sequencing experiments of drug-exposed bacteria revealed strong upregulation of a distinct set of genes including ethA, encoding a monooxygenase activating the anti-tuberculous prodrug ethionamide. Accordingly, we found a strong ethionamide boosting effect in S3-treated Mtb. Extensive structure-activity relationship experiments revealed that anti-virulence and ethionamide-boosting activity can be uncoupled by chemical modification of the primary hit molecule. To conclude, this series of dual-active oxadiazole compounds targets Mtb via two distinct mechanisms of action.