Synthesis and biological evaluation of 1,3,4-thiadiazole derivatives as type III secretion system inhibitors against Xanthomonas oryzae

Design and Synthesis of Mandelic Acid Derivatives for Suppression of Virulence via T3SS against Citrus Canker

Citrus canker, a highly contagious bacterial disease caused by Xanthomonas citri subsp. citri (Xcc), poses a substantial threat to citrus crops, leading to serious reductions in fruit yield and economic losses. Most commonly used bactericides against Xcc lead to the rapid development of resistant subpopulations. Therefore, it is imperative to create novel drugs, such as type III secretion system (T3SS) inhibitors, that specifically target bacterial virulence factors rather than bacterial viability. In our study, we designed and synthesized a series of mandelic acid derivatives including 2-mercapto-1,3,4-thiazole. Seven substances were found to reduce the level of transcription of hpa1 without affecting bacterial viability. In vivo bioassays indicated that compound F9 significantly inhibited hypersensitive response and pathogenicity. RT-qPCR assays showed that compound F9 visibly suppressed the expression of Xcc T3SS-related genes as well as citrus canker susceptibility gene CsLOB1. Furthermore, the combination with compound F9 and quorum-quenching bacteria HN-8 can also obviously alleviate canker symptoms.

Application and Mechanism of Cryptolepine and Neocryptolepine Derivatives as T3SS Inhibitors for Control of Bacterial Leaf Blight on Rice

Bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv oryzae (Xoo) is extremely harmful to rice production. The traditional control approach is to use bactericides that target key bacterial growth factors, but the selection pressure on the pathogen makes resistant strains the dominant bacterial strains, leading to a decline in bactericidal efficacy. Type III secretion system (T3SS) is a conserved and critical virulence factor in most Gram-negative bacteria, and its expression or absence does not affect bacterial growth, rendering it an ideal target for creating drugs against Gram-negative pathogens. In this work, we synthesized a range of derivatives from cryptolepine and neocryptolepine. We found that compound Z-8 could inhibit the expression of Xoo T3SS-related genes without affecting the growth of bacteria. an in vivo bioassay showed that compound Z-8 could effectively reduce the hypersensitive response (HR) induced by Xoo in tobacco and reduce the pathogenicity of Xoo in rice. Furthermore, it exhibited synergy in control of bacterial leaf blight when combined with the quorum quenching bacterial F20.

Derivative of cinnamic acid inhibits T3SS of Xanthomonas oryzae pv. oryzae through the HrpG-HrpX regulatory cascade

Bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv. oryzae (Xoo) has a significant impact on rice yield and quality worldwide. Traditionally, bactericide application has been commonly used to control this devastating disease. However, the overuse of fungicides has led to a number of problems such as the development of resistance and environmental pollution. Therefore, the development of new methods and approaches for disease control are still urgent. In this paper, a series of cinnamic acid derivatives were designed and synthesized, and three novel T3SS inhibitors A10, A12 and A20 were discovered. Novel T3SS inhibitors A10, A12 and A20 significantly inhibited the hpa1 promoter activity without affecting Xoo growth. Further studies revealed that the title compounds A10, A12 and A20 significantly impaired hypersensitivity in non-host plant tobacco leaves, while applications on rice significantly reduced symptoms of bacterial leaf blight. RT-PCR showed that compound A20 inhibited the expression of T3SS-related genes. In summary, this work exemplifies the potential of the title compound as an inhibitor of T3SS and its efficacy in the control of bacterial leaf blight.

Novel mandelic acid derivatives suppress virulence of Ralstonia solanacearum via type III secretion system

BACKGROUND

Bacterial wilt induced by Ralstonia solanacearum is regarded as one of the most devastating diseases. However, excessive and repeated use of the same bactericides has resulted in development of bacterial resistance. Targeting bacterial virulence factors, such as type III secretion system (T3SS), without inhibiting bacterial growth is a possible assay to discover new antimicrobial agents.

RESULTS

In this work, identifying new T3SS inhibitors, a series of mandelic acid derivatives with 2-mercapto-1,3,4-thiazole moiety was synthesized. One of them, F-24, inhibited the transcription of hrpY gene significantly. The presence of this compound obviously attenuated hypersensitive response (HR) without inhibiting bacterial growth of R. solanacearum. The transcription levels of those typical T3SS genes were reduced to various degrees. The test of the ability of F-24 in protecting plants demonstrated that F-24 protected tomato plants against bacterial wilt without restricting the multiplication of R. solanacearum. The mechanism of this T3SS inhibition is through the PhcR-PhcA-PrhG-HrpB pathway.

CONCULSION

The screened F-24 could inhibit R. solanacearum T3SS and showed better inhibitory activity than previously reported inhibitors without affecting the growth of the strain, and F-24 is a compound with good potential in the control of R. solanacearum. © 2023 Society of Chemical Industry.

Novel pyrimidin-4-one derivatives as potential T3SS inhibitors against Xanthomonas campestris pv. campestris

BACKGROUND

Cruciferous black rot is caused by Xanthomonas campestris pv. campestris (Xcc) infection and is a widespread disease worldwide. Excessive and repeated use of bactericide is an important cause of the development of bacterial resistance. It is imperative to take new approaches to screening compounds that target virulence factors rather than kill bacterial pathogens. The type III secretion system (T3SS) invades a variety of cells by transporting virulence effector factors into the cytoplasm and is an attractive antitoxic target. Toward the search of new T3SS inhibitors, an alternative series of novel pyrimidin-4-one derivatives were designed and synthesized and assessed for their effect in blocking the virulence.

RESULTS

All of the target compounds were characterized by proton (1 H) nuclear magnetic resonance (NMR), carbon-13 (13 C) NMR, fluorine-19 (19 F) NMR and high-resolution mass spectrometry (HRMS). All compounds were evaluated using high-throughput screening systems against Xcc. The results of the biological activity test revealed that the compound SPF-9 could highly inhibit the activity of xopN gene promoter and the hypersensitivity (HR) of tobacco without affecting bacterial growth. Moreover, messenger RNA (mRNA) level measurements showed that compound SPF-9 inhibited the expression of some representative genes (hrp/hrc genes). Compound SPF-9 weakened the pathogenicity of Xcc to Raphanus sativus L.

CONCLUSION

Compound SPF-9 has good potential for further development as a novel T3SS inhibitor against Xcc. © 2023 Society of Chemical Industry.

Novel Ethyl-3-Aryl-2-Nitroacrylate Derivatives as Potential T3SS Inhibitors against Xanthomonas oryzae pv. oryzae on Rice

Bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is a highly destructive bacterial disease. Traditional prevention methods have utilized antibiotics to target bacterial growth, which has accelerated the emergence of resistant strains. New prevention techniques are developing agents such as type III secretion system (T3SS) inhibitors that target bacterial virulence factors without affecting bacterial growth. To explore novel T3SS inhibitors, a series of ethyl-3-aryl-2-nitroacrylate derivatives were designed and synthesized. Preliminary screening of T3SS inhibitors was based on the inhibition of the hpa1 gene promoter and showed no effect on bacterial growth. Compounds B9 and B10, obtained in the primary screening, significantly inhibited the hypersensitive response (HR) in tobacco and the expression of T3SS genes in the hrp cluster including key regulatory genes. In vivo bioassays showed that T3SS inhibitors obviously inhibited BLB and appeared to be more effective when combined with quorum quenching bacteria F20.

Exploiting Natural Maltol for Synthesis of Novel Hydroxypyridone Derivatives as Promising Anti-Virulence Agents in Bactericides Discovery

Anti-infection strategies based on suppression of bacterial virulence factors represent a crucial direction for the development of new antibacterial agents to address the resistance triggered by traditional drugs'/pesticides' bactericidal activity. To identify and obtain more effective and diverse molecules targeting virulence, we prepared a series of 3-hydroxy-2-methyl-1-pyridin-4-(1H)-one derivatives and evaluated their antibacterial behaviors. Compound B₆ exhibited the highest bioactivity, with half-maximal effective concentration (EC₅₀) values ranging fro9m 10.03 to 30.16 μg mL^-1 against three plant pathogenic bacteria. The antibacterial mechanism showed that it could considerably reduce various virulence factors (such as extracellular enzymes, biofilm, and T3SS effectors) and inhibit the expression of virulence factor-related genes. In addition, the control efficiency of compound B₆ against rice bacterial leaf blight at 200 μg mL^-1 was 46.15-49.15%, and their control efficiency was improved by approximately 12% after the addition of pesticide additives. Thus, a new class of bactericidal candidates targeting bacterial virulence factors was developed for controlling plant bacterial diseases.

Synthesis and biological evaluation of 2,5-disubstituted furan derivatives containing 1,3-thiazole moiety as potential α-glucosidase inhibitors

α-Glucosidase, which is involved in the hydrolysis of carbohydrates to glucose and directly mediates blood glucose elevation, is a crucial therapeutic target for type 2 diabetes. In this work, 2,5-disubstituted furan derivatives containing 1,3-thiazole-2-amino or 1,3-thiazole-2-thiol moiety (III-01 ∼ III-30) were synthesized and screened for their inhibitory activity against α-glucosidase. α-Glucosidase inhibition assay demonstrated that all compounds had IC₅₀ in the range of 0.645-94.033 μM and more potent than standard inhibitor acarbose (IC₅₀ = 452.243 ± 54.142 µM). The most promising inhibitors of the two series were compound III-10 (IC₅₀ = 4.120 ± 0.764 μM) and III-24 (IC₅₀ = 0.645 ± 0.052 μM), respectively. Kinetic study and molecular docking simulation revealed that compound III-10 (Ki = 2.04 ± 0.72 μM) is a competitive inhibitor and III-24 (Ki = 0.44 ± 0.53 μM) is a noncompetitive inhibitor against α-glucosidase. Significantly, these two compounds showed nontoxicity towards HEK293, RAW264.7 and HepG2 cells, suggesting that compounds may be considered as a class of potential candidates for further developing novel antidiabetic drugs.

Research Progress on Small Molecular Inhibitors of the Type 3 Secretion System

The overuse of antibiotics has led to severe bacterial drug resistance. Blocking pathogen virulence devices is a highly effective approach to combating bacterial resistance worldwide. Type three secretion systems (T3SSs) are significant virulence factors in Gram-negative pathogens. Inhibition of these systems can effectively weaken infection whilst having no significant effect on bacterial growth. Therefore, T3SS inhibitors may be a powerful weapon against resistance in Gram-negative bacteria, and there has been increasing interest in the research and development of T3SS inhibitors. This review outlines several reported small-molecule inhibitors of the T3SS, covering those of synthetic and natural origin, including their sources, structures, and mechanisms of action.

Design, synthesis, and bioactivity of ferulic acid derivatives containing an β-amino alcohol

Background

Plant diseases caused by viruses and bacteria cause huge economic losses due to the lack of effective control agents. New potential pesticides can be discovered through biomimetic synthesis and structural modification of natural products. A series of ferulic acid derivatives containing an β-amino alcohol were designed and synthesized, and their biological activities were evaluated.

Result

Bioassays results showed that the EC₅₀ values of compound D24 against Xanthomonas oryzae pv. oryzae (Xoo) was 14.5 μg/mL, which was better than that of bismerthiazol (BT, EC₅₀ = 16.2 μg/mL) and thiodiazole copper (TC, EC₅₀ = 44.5 μg/mL). The in vivo curative and protective activities of compound D24 against Xoo were 50.5% and 50.1%, respectively. The inactivation activities of compounds D2, D3 and D4 against tobacco mosaic virus (TMV) at 500 μg/mL were 89.1, 93.7 and 89.5%, respectively, superior to ningnanmycin (93.2%) and ribavirin (73.5%). In particular, the EC₅₀ value of compound D3 was 38.1 μg/mL, and its molecular docking results showed that compound D3 had a strong affinity for TMV-CP with a binding energy of − 7.54 kcal/mol, which was superior to that of ningnanmycin (− 6.88 kcal /mol).

Conclusions

The preliminary mechanism research results indicated that compound D3 may disrupt the three-dimensional structure of the TMV coat protein, making TMV particles unable to self-assemble, which may provide potential lead compounds for the discovery of novel plant antiviral agents.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13065-022-00828-8.

A small molecule, C24H17ClN4O2S, inhibits the function of the type III secretion system in Salmonella Typhimurium

Background

Salmonella enterica serovar Typhimurium (S. Typhimurium) causes gastroenteritis and diarrhea in humans and food-producing animals. The type III secretion system (T3SS) has been known to be a potent virulence mechanism by injecting effector proteins into the cytosol of host cells. S. Typhimurium encodes two T3SSs by Salmonella pathogenicity islands 1 and 2. Previous studies showed that T3SS shared a potent virulence mechanism and molecular structure among several gram-negative bacteria. Therefore, T3SS has been identified as an attractive target in the development of novel therapeutics for the treatment of bacterial infections. Several studies reported that small-molecule compounds are able to inhibit functions of bacterial T3SSs. A small molecule, C₂₄H₁₇ClN₄O₂S, has been shown the ability to inhibit the activity of Yersinia pestis T3SS ATPase, YscN, resulting to block the secretion of effector proteins. In this study, we studied the effects and mechanism for SPI-1 T3SS inhibition of this compound in S. Typhimurium.

Results

We demonstrated that this compound prohibited the secretion of effector proteins from Salmonella via SPI-1 T3SS at 100 μM. As the result, bacterial invasion ability into epithelial cell cultures was reduced. In contrast with previous study, the C₂₄H₁₇ClN₄O₂S molecule did not inactivate the activity of SPI-1 T3SS ATPase, InvC, in Salmonella. However, we studied the global cellular effects of S. Typhimurium after being treated with this compound using a quantitative proteomic technique. These proteomic results showed that the main SPI-1 transcription regulator, InvF, and two effector proteins, SipA and SipC, were reduced in bacterial cells treated with the compound.

Conclusions

It may explain that action of the small-molecule compound, C₂₄H₁₇ClN₄O₂S, for blocking the secretion of SPI-1 T3SS in Salmonella is through inhibition of SPI-1 regulator, InvF, expression. Further studies are necessary to identify specific mechanisms for inhibition between this small-compound and InvF SPI-1 regulator protein.

Synthesis and Biological Evaluation of 1,2,4-Triazole Thioethers as Both Potential Virulence Factor Inhibitors against Plant Bacterial Diseases and Agricultural Antiviral Agents against Tobacco Mosaic Virus Infections

Targeting the virulence factors of phytopathogenic bacteria is an innovative strategy for alleviating or eliminating the pathogenicity and rapid outbreak of plant microbial diseases. Therefore, several types of 1,2,4-triazole thioethers bearing an amide linkage were prepared and screened to develop virulence factor inhibitors. Besides, the 1,2,4-triazole scaffold was exchanged by a versatile 1,3,4-oxadiazole core to expand molecular diversity. Bioassay results revealed that a 1,2,4-triazole thioether A₁₀ bearing a privileged N-(3-nitrophenyl)acetamide fragment was extremely bioactive against Xanthomonas oryzae pv. oryzae (Xoo) with an EC₅₀ value of 5.01 μg/mL. Label-free quantitative proteomics found that compound A₁₀ could significantly downregulate the expression of Xoo's type III secretion system (T3SS) and transcription activator-like effector (TALE) correlative proteins. Meanwhile, qRT-PCR detection revealed that the corresponding gene transcription levels of these virulence factor-associated proteins were substantially inhibited after being triggered by compound A₁₀. As a result, the hypersensitive response and pathogenicity were strongly depressed, indicating that a novel virulence factor inhibitor (A₁₀) was probably discovered. In vivo anti-Xoo trials displayed that compound A₁₀ yielded practicable control efficiency (54.2-59.6%), which was superior to thiadiazole-copper and bismerthiazol (38.1-44.9%). Additionally, compound A₁₀ showed an appreciable antiviral activity toward tobacco mosaic virus (TMV) with the curative and protective activities of 54.6 and 76.4%, respectively, which were comparable to ningnanmycin (55.2 and 60.9%). This effect was further validated and visualized by the inoculation test using GFP-labeled TMV, thereby leading to the reduced biosynthesis of green-fluorescent TMV on Nicotiana benthamiana. Given the outstanding features of compound A₁₀, it should be deeply developed as a versatile agricultural chemical.

Discovery of a series of 5-phenyl-2-furan derivatives containing 1,3-thiazole moiety as potent Escherichia coli β-glucuronidase inhibitors

Gut microbial β-glucuronidases have drawn much attention due to their role as a potential therapeutic target to alleviate some drugs or their metabolites-induced gastrointestinal toxicity. In this study, fifteen 5-phenyl-2-furan derivatives containing 1,3-thiazole moiety (1-15) were synthesized and evaluated for their inhibitory effects against Escherichia coli β-glucuronidase (EcGUS). Twelve of them showed satisfactory inhibition against EcGUS with IC₅₀ values ranging from 0.25 μM to 2.13 μM with compound 12 exhibited the best inhibition. Inhibition kinetics studies indicated that compound 12 (K_i = 0.14 ± 0.01 μM) was an uncompetitive inhibitor for EcGUS and molecular docking simulation further predicted the binding model and capability of compound 12 with EcGUS. A preliminary structure-inhibitory activity relationship study revealed that the heterocyclic backbone and bromine substitution of benzene may be essential for inhibition against EcGUS. The compounds have the potential to be applied in drug-induced gastrointestinal toxicity and the findings would help researchers to design and develop more effective 5-phenyl-2-furan type EcGUS inhibitors.

Thiazolidin-2-cyanamides derivatives as novel potent Escherichia coli β-glucuronidase inhibitors and their structure-inhibitory activity relationships

Gut microbial β-glucuronidases have the ability to deconjugate glucuronides of some drugs, thus have been considered as an important drug target to alleviate the drug metabolites-induced gastrointestinal toxicity. In this study, thiazolidin-2-cyanamide derivatives containing 5-phenyl-2-furan moiety (1–13) were evaluated for inhibitory activity against Escherichia coli β-glucuronidase (EcGUS). All of them showed more potent inhibition than a commonly used positive control, d-saccharic acid 1,4-lactone, with the IC₅₀ values ranging from 1.2 µM to 23.1 µM. Inhibition kinetics studies indicated that compound 1–3 were competitive type inhibitors for EcGUS. Molecular docking studies were performed and predicted the potential molecular determinants for their potent inhibitory effects towards EcGUS. Structure–inhibitory activity relationship study revealed that chloro substitution on the phenyl moiety was essential for EcGUS inhibition, which would help researchers to design and develop more effective thiazolidin-2-cyanamide type inhibitors against EcGUS.

Type 3 secretion system as an anti-Pseudomonal target

Type 3 secretion systems (T3SSs) are a series of mechanisms involved in bacterial pathogenesis. While Pseudomonas aeruginosa only possess one T3SS, it plays a key role in the virulence of P. aeruginosa virulence. This finding suggests that T3SS impairment may be an alternative for antimicrobial agents, allowing P. aeruginosa infections to be directly combated avoiding antimicrobial pressure on this and other microorganisms. To date, different approaches have been proposed, including T3SS inhibition, vaccination strategies, development of anti-T3SS antibodies and gene silencing.

2,5-Disubstituted furan derivatives containing 1,3,4-thiadiazole moiety as potent α-glucosidase and E. coli β-glucuronidase inhibitors

In this paper, the 2,5-disubstituted furan derivatives containing 1,3,4-thiadiazole were synthesized and screened for their inhibitory activity against α-glucosidase and β-glucuronidases to obtain potent α-glucosidase inhibitor 9 (IC₅₀ = 0.186 μM) and E. coli β-glucuronidase inhibitor 26 (IC₅₀ = 0.082 μM), respectively. The mechanisms of the compounds were studied. The kinetic study revealed that compound 9 is a competitive inhibitor against α-glucosidase (Ki = 0.05 ± 0.003 μM) and molecular docking simulation showed several key interactions between 9 and the target including hydrogen bond and p-π stacking interaction. Derivative 26 (Ki = 0.06 ± 0.005 μM) displayed uncompetitive inhibition behavior against EcGUS. Furthermore, the result of docking revealed the furan ring of 26 may be a key moiety in obstructing the active domain of EcGUS. In addition, compound 15 exhibited significant inhibitory activity against these two enzymes, with potential therapeutic effects against diabetes and against CPT-11-induced diarrhea. At the same time, their low toxicity against normal liver tissue LO2 cells lays the foundation for in vivo studies and the development of bifunctional drug.

Novel S-Thiazol-2-yl-furan-2-carbothioate Derivatives as Potential T3SS Inhibitors Against Xanthomonas oryzae on Rice

Bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv oryzae (Xoo) is considered as the most destructive disease of rice. The use of bactericides is among the most widely used traditional methods to control this destructive disease. The excessive and repeated use of the same bactericides is also becoming the reason behind the development of bactericide resistance. The widely used method for finding the new antimicrobial agents often involves the bacterial virulence factors as a target without affecting bacterial growth. Type III secretion system (T3SS) is a protein appendage and is considered as having essential virulence factors in most Gram-negative bacteria. Due to the conserved construct, T3SS has been regarded as an important mark for the blooming of novel antimicrobial drugs. Toward the search of new T3SS inhibitors, an alternative series of 1,3-thiazole derivatives were designed and synthesized. Their structures were characterized and confirmed by ¹H NMR, ¹³C NMR, MS, and elemental analysis. All the title compounds inhibited the promoter activity of hpa1 gene significantly. Eight of them showed better inhibition than our previous T3SS inhibitor TS006 (o-coumaric acid, OCA). The treatment of Xoo with eight compounds significantly attenuated HR without affecting bacterial growth. The mRNA levels of some representative genes (hrp/hrc genes) were reduced up to different extents. In vivo bioassay results showed that eight T3SS inhibitors could reduce bacterial leaf blight and bacterial leaf streak symptoms on rice, significantly.