Synthesis, quorum sensing inhibition and docking studies of 1,5-dihydropyrrol-2-ones

Trichoderma-derived emodin competes with ExpR and ExpI of Pectobacterium carotovorum subsp. carotovorum to biocontrol bacterial soft rot

BACKGROUND

Quorum sensing inhibitors (QSIs) are an emerging control tool that inhibits the quorum sensing (QS) system of pathogenic bacteria. We aimed to screen for potential QSIs in the metabolites of Trichoderma and to explore their inhibitory mechanisms.

RESULTS

We screened a strain of Trichoderma asperellum LN004, which demonstrated the ability to inhibit the color development of Chromobacterium subtsugae CV026, primarily attributed to the presence of emodin as its key QSI component. The quantitative polymerase chain reaction with reverse transcription results showed that after emodin treatment of Pectobacterium carotovorum subsp. carotovorum (Pcc), plant cell wall degrading enzyme-related synthetic genes were significantly downregulated, and the exogenous enzyme synthesis gene negative regulator (rsmA) was upregulated 3.5-fold. Docking simulations indicated that emodin could be a potential ligand for ExpI and ExpR proteins because it exhibited stronger competition than the natural ligands in Pcc. In addition, western blotting showed that emodin attenuated the degradation of n-acylhomoserine lactone on the ExpR protein and protected it. Different concentrations of emodin reduced the activity of pectinase, cellulase, and protease in Pcc by 20.81%-72.21%, 8.38%-52.73%, and 3.57%-47.50%. Lesion size in Chinese cabbages, carrots and cherry tomatoes following Pcc infestation was reduced by 10.02%-68.57%, 40.17%-88.56% and 11.36%-86.17%.

CONCLUSION

Emodin from T. asperellum LN004 as a QSI can compete to bind both ExpI and ExpR proteins, interfering with the QS of Pcc and reducing the production of virulence factors. The first molecular mechanism reveals the ability of emodin as a QSI to competitively inhibit two QS proteins simultaneously. © 2023 Society of Chemical Industry.

Synthesis, in Silico Study and Biological Evaluation of N-(Benzothiazol/Thiazol-2-yl)benzamide Derivatives as Quorum Sensing Inhibitors against Pseudomonas aeruginosa

The development of bacterial resistance to chemical therapy poses a severe danger to efficacy of treating bacterial infections. One of the key factors for resistance to antimicrobial medications is growth of bacteria in biofilm. Quorum sensing (QS) inhibition was created as an alternative treatment by developing novel anti-biofilm medicines. Cell-cell communication is impeded by QS inhibition, which targets QS signaling pathway. The goal of this work is to develop newer drugs that are effective against Pseudomonas aeruginosa by decreasing QS and acting as anti-biofilm agents. In this investigation, N-(benzo[d]thiazol-2-yl)benzamide/N-(thiazol-2-yl)benzamide derivatives 3a-h were designed and synthesized in good yields. Further, molecular docking analyses revealed that binding affinity values were founded -11.2 to -7.6 kcal/mol that were moderate to good. The physicochemical properties of these prepared compounds were investigated through in-silico method. Molecular dynamic simulation was also used to know better understanding of stability of the protein and ligand complex. Comparing N-(benzo[d]thiazol-2-yl)benzamide 3a to salicylic acid (4.40±0.10) that was utilised as standard for quorum sensing inhibitor, the anti-QS action was found greater for N-(benzo[d]thiazol-2-yl)benzamide 3a (4.67±0.45) than salicylic acid (4.40±0.10). Overall, research results suggested that N-(benzo[d]thiazol-2-yl)benzamide/N-(thiazol-2-yl)benzamide derivatives 3a-h may hold to develop new quorum sensing inhibitors.

Quorum sensing inhibitors as Therapeutics: Bacterial biofilm inhibition

The overuse and inappropriate use of antibiotics to treat bacterial infections has led to the development of multiple drug resistant strains. Biofilm is a complex microorganism aggregation defined by the presence of a dynamic, sticky, and protective extracellular matrix made of polysaccharides, proteins, and nucleic acids. The infectious diseases are caused by bacteria that flourish within quorum sensing (QS) mediated biofilms. Efforts to disrupt biofilms have enabled the identification of bioactive molecules produced by prokaryotes and eukaryotes. The QS system is quenched predominantly by these molecules. The phenomenon is also termed as quorum sensing (QS). Both synthetic and natural substances have been discovered to be useful in QS. This review describes natural and synthetic quorum sensing inhibitors (QSIs) with the potential to treat bacterial infections. It includes the discussion on quorum sensing, mechanism of quorum sensing, effect of substituents on the activity. These discoveries could result in effective therapies using far lower dosages of medications, particularly antibiotics, are currently needed.

Synthesis, Biological Evaluation and in Silico Study of N-(2- and 3-Pyridinyl)benzamide Derivatives as Quorum Sensing Inhibitors against Pseudomonas aeruginosa

The effectiveness of treating bacterial infections is seriously threatened by the emergence of bacterial resistance to chemical treatment. Growth of microbes in biofilm is one of the main causes of resistance to antimicrobial drugs. Quorum sensing (QS) inhibition, which targets the QS signalling system by obstructing cell-cell communication, was developed as an alternative treatment by creating innovative anti-biofilm drugs. Therefore, the goal of this study is to develop novel antimicrobial drugs that are effective against Pseudomonas aeruginosa by inhibiting QS and acting as anti-biofilm agents. In this study, N-(2- and 3-pyridinyl)benzamide derivatives were selected to design and syntheses. Antibiofilm activity was revealed by all the synthesized compounds and the biofilm was visibly impaired, and the OD_595nm readings of solubilized biofilm cells presented a momentous difference between the treated and untreated biofilms. The best anti-QS zone was observed for compound 5d and found to be 4.96 mm. Through in silico research, the physicochemical characteristics and binding manner of these produced compounds were examined. For the purpose of understanding the stability of the protein and ligand complex, molecular dynamic simulation was also carried out. The overall findings showed that N-(2- and 3-pyridinyl)benzamide derivatives could be the key to creating effective newer anti-quorum sensing drugs that are effective against different bacteria.

Investigation of halogenated furanones as inhibitors of quorum sensing-regulated bioluminescence in Vibrio harveyi

Aim: Vibrio harveyi is a Gram-negative marine bacterium that is a model system in the study of quorum sensing (QS). V. harveyi uses multichannel QS, mediated by three signaling molecules. The aim of this study was to synthesize and screen a diverse series of furanones for their potential to inhibit V. harveyi quorum sensing. Materials & methods: A library of halogenated furanones was prepared and derivatized using standard Pd-mediated coupling reactions and subsequently evaluated for their effects on V. harveyi bioluminescence. Results & conclusion: Several furanones inhibited QS-regulated bioluminescence, with gem-dichlorofuranone and tribromofuranone compounds proving especially effective. Importantly, a number of compounds were effective inhibitors of V. harveyi bioluminescence but did not have an impact on bacterial growth.

Synthesis of Alkyne-Substituted Dihydropyrrolones as Bacterial Quorum-Sensing Inhibitors of Pseudomonas aeruginosa

The Quorum-sensing system in Pseudomonas aeruginosa is responsible for the pathogenicity and the production of virulence factors and biofilm formation. Dihydropyrrolones were previously found to act as inhibitors of QS-dependent bacterial phenotypes. In this study, a range of dihydropyrrolone (DHP) analogues was synthesized via the lactone-lactam conversion of lactone intermediates followed by the formation of novel acetylene analogues of dihydropyrrolones from brominated dihydropyrrolones via Sonogashira coupling reactions in moderate to high yields. Upon biological testing, the most potent compounds, 39–40 and 44, showed higher bacterial quorum-sensing inhibitory (QSI) activity against P. aeruginosa reporter strain at 62.5 µM. Structure–activity relationship studies revealed that di-alkynyl substituent at the exocyclic position of DHPs possessed higher QSI activities than those of mono-alkynyl DHPs. Moreover, a hexyl-substituent at C3 of DHPs was beneficial to QSI activity while a phenyl substituent at C4 of DHPs was detrimental to QSI activity of analogues.

Heterocyclic Chemistry Applied to the Design of N-Acyl Homoserine Lactone Analogues as Bacterial Quorum Sensing Signals Mimics

N-acyl homoserine lactones (AHLs) are small signaling molecules used by many Gram-negative bacteria for coordinating their behavior as a function of their population density. This process, based on the biosynthesis and the sensing of such molecular signals, and referred to as Quorum Sensing (QS), regulates various gene expressions, including growth, virulence, biofilms formation, and toxin production. Considering the role of QS in bacterial pathogenicity, its modulation appears as a possible complementary approach in antibacterial strategies. Analogues and mimics of AHLs are therefore biologically relevant targets, including several families in which heterocyclic chemistry provides a strategic contribution in the molecular design and the synthetic approach. AHLs consist of three main sections, the homoserine lactone ring, the central amide group, and the side chain, which can vary in length and level of oxygenation. The purpose of this review is to summarize the contribution of heterocyclic chemistry in the design of AHLs analogues, insisting on the way heterocyclic building blocks can serve as replacements of the lactone moiety, as a bioisostere for the amide group, or as an additional pattern appended to the side chain. A few non-AHL-related heterocyclic compounds with AHL-like QS activity are also mentioned.

Growing emergence of drug-resistant Pseudomonas aeruginosa and attenuation of its virulence using quorum sensing inhibitors: A critical review

A perilous increase in the number of bacterial infections has led to developing throngs of antibiotics for increasing the quality and expectancy of life. Pseudomonas aeruginosa is becoming resistant to all known conventional antimicrobial agents thereby posing a deadly threat to the human population. Nowadays, targeting virulence traits of infectious agents is an alternative approach to antimicrobials that is gaining much popularity to fight antimicrobial resistance. Quorum sensing (QS) involves interspecies communication via a chemical signaling pathway. Under this mechanism, cells work in a concerted manner, communicate with each other with the help of signaling molecules called auto-inducers (AI). The virulence of these strains is driven by genes, whose expression is regulated by AI, which in turn acts as transcriptional activators. Moreover, the problem of antibiotic-resistance in case of infections caused by P. aeruginosa becomes more alarming among immune-compromised patients, where the infectious agents easily take over the cellular machinery of the host while hidden in the QS mediated biofilms. Inhibition of the QS circuit of P. aeruginosa by targeting various signaling pathways such as LasR, RhlR, Pqs, and QScR transcriptional proteins will help in blocking downstream signal transducers which could result in reducing the bacterial virulence. The anti-virulence agent does not pose an immediate selective pressure on growing bacterium and thus reduces the pathogenicity without harming the target species. Here, we review exclusively, the growing emergence of multi-drug resistant (MDR) P. aeruginosa and the critical literature survey of QS inhibitors with their potential application of blocking P. aeruginosa infections.

Preparation of 3,5-diarylsubstituted 5-hydroxy-1,5-dihydro-2H-pyrrol-2-ones via base-assisted cyclization of 3-cyanoketones

A convenient preparative method is developed allowing for expeditious assembly of 3,5-diarylsubstituted 5-hydroxy-1,5-dihydro-2H-pyrrol-2-ones from routinely available inexpensive synthetic precursors. These compounds could not be prepared via the previously known protocols, as 2-aminofuran derivatives were produced instead.

Design and synthesis of aryl-substituted pyrrolidone derivatives as quorum sensing inhibitors

Quorum sensing, a common cell-to-cell communication system, is considered to have promising application in antibacterial therapy since they are expected to induce lower bacterial resistance than conventional antibiotics. However, most of present quorum sensing inhibitors have potent cell toxicity, which limits their application. In this study we evaluated the diverse quorum sensing inhibition activities of different biaromatic furanones and brominated pyrrolones. On this basis, we further designed and synthesized a new series of aryl-substituted pyrrolones 12a-12f. In the quorum sensing inhibition assay, compound 12a showed improved characteristics and low toxicity against human hepatocellular carcinoma cell. In particular, it can inhibit the pyocyanin production and protease activity of Pseudomonas aeruginosa by 80.6 and 78.5%, respectively. Besides, in this series, some compounds exerted moderate biofilm inhibition activity. To sum up, all the findings indicate that aryl-substituted pyrrolidone derivatives are worth further investigation as quorum sensing inhibitors.

Structure-activity relationships of furanones, dihydropyrrolones and thiophenones as potential quorum sensing inhibitors

Since their initial isolation from the marine alga Delisea pulchra, bromofuranones have been investigated as potential inhibitors of quorum sensing (QS) in various bacterial strains. QS is an important mechanism by which bacteria co-ordinate their molecular response to the environment. QS is intrinsically linked to bacterial antibiotic resistance. Inspired by nature, chemists have developed a wide variety of synthetic analogs in an effort to elucidate the structure-activity relationships of these compounds, and to ultimately develop novel antimicrobial agents. In this work, we describe advances in this field while paying particular attention to apparent structure-activity relationships. This review is organized according to the main ring systems under investigation, namely furanones, dihydropyrrolones and thiophenones.

Functional Diversity of Quorum Sensing Receptors in Pathogenic Bacteria: Interspecies, Intraspecies and Interkingdom Level

The formation of biofilm by pathogenic bacteria is considered as one of the most powerful mechanisms/modes of resistance against the action of several antibiotics. Biofilm is formed as a structural adherent over the surfaces of host, food and equipments etc. and is further functionally coordinated by certain chemicals produced itself. These chemicals are known as quorum sensing (QS) signaling molecules and are involved in the cross talk at interspecies, intraspecies and interkingdom levels thus resulting in the production of virulence factors leading to pathogenesis. Bacteria possess receptors to sense these chemicals, which interact with the incoming QS molecules. It is followed by the secretion of virulence molecules, regulation of bioluminescence, biofilm formation, antibiotic resistance development and motility behavioral responses. In the natural environment, different bacterial species (Gram-positive and Gram-negative) produce QS signaling molecules that are structurally and functionally different. Recent and past research shows that various antagonistic molecules (naturally and chemically synthesized) are characterized to inhibit the formation of biofilm and attenuation of bacterial virulence by blocking the QS receptors. This review article describes about the diverse QS receptors at their structural, functional and production levels. Thus, by blocking these receptors with inhibitory molecules can be a potential therapeutic approach to control pathogenesis. Furthermore, these receptors can also be used as a structural platform to screen the most potent inhibitors with the help of bioinformatics approaches.

Total synthesis, structural revision and biological evaluation of γ-elemene-type sesquiterpenes

Total synthesis and absolute configuration confirmation of γ-elemene-type sesquiterpenes, which possess vast potential for biological activities, was investigated based on a convergent synthetic strategy. A key intermediate with all functional groups of this family of natural products was accessed by an intermolecular aldol reaction and then an acetylation of a known ketone (12) derived from commercially available verbenone. The versatile intermediate can be easily transformed into structurally different γ-elemene-type sesquiterpenes based on control of base-promoted cyclization manipulation in different solvents. The utility of this robust approach is illustrated by the first syntheses of elema-1,3,7(11),8-tetraen-8,12-lactam (4') and 8β-methoxy-isogermafurenolide (6a), as well as the syntheses of elem-1,3,7,8-tetraen-8,12-olide (3) and hydroxyisogermafurenolide (5) in only 6 or 7 steps. In addition, the structure of the reported 5βH-elem-1,3,7,8-tetraen-8,12-olide (1) was revised as elem-1,3,7,8-tetraen-8,12-olide (3) by comparison of their identified datum, and the absolute configuration of elema-1,3,7(11),8-tetraen-8,12-lactam was confirmed as 4'. Furthermore, the inhibitory effect of all synthesized natural compounds and their natural analogues on cancer cell proliferation was evaluated. Among them compounds 3, 4 and 4' were found to possess potent inhibitory activity against Kasumi-1 and Pfeiffer. Meanwhile, preliminary structure-activity relationships for these compounds are discussed.

Widespread Existence of Quorum Sensing Inhibitors in Marine Bacteria: Potential Drugs to Combat Pathogens with Novel Strategies

Quorum sensing (QS) is a phenomenon of intercellular communication discovered mainly in bacteria. A QS system consisting of QS signal molecules and regulatory protein components could control physiological behaviors and virulence gene expression of bacterial pathogens. Therefore, QS inhibition could be a novel strategy to combat pathogens and related diseases. QS inhibitors (QSIs), mainly categorized into small chemical molecules and quorum quenching enzymes, could be extracted from diverse sources in marine environment and terrestrial environment. With the focus on the exploitation of marine resources in recent years, more and more QSIs from the marine environment have been investigated. In this article, we present a comprehensive review of QSIs from marine bacteria. Firstly, screening work of marine bacteria with potential QSIs was concluded and these marine bacteria were classified. Afterwards, two categories of marine bacteria-derived QSIs were summarized from the aspects of sources, structures, QS inhibition mechanisms, environmental tolerance, effects/applications, etc. Next, structural modification of natural small molecule QSIs for future drug development was discussed. Finally, potential applications of QSIs from marine bacteria in human healthcare, aquaculture, crop cultivation, etc. were elucidated, indicating promising and extensive application perspectives of QS disruption as a novel antimicrobial strategy.

Recent Advances in Anti-virulence Therapeutic Strategies With a Focus on Dismantling Bacterial Membrane Microdomains, Toxin Neutralization, Quorum-Sensing Interference and Biofilm Inhibition

Antimicrobial resistance constitutes one of the major challenges facing humanity in the Twenty-First century. The spread of resistant pathogens has been such that the possibility of returning to a pre-antibiotic era is real. In this scenario, innovative therapeutic strategies must be employed to restrict resistance. Among the innovative proposed strategies, anti-virulence therapy has been envisioned as a promising alternative for effective control of the emergence and spread of resistant pathogens. This review presents some of the anti-virulence strategies that are currently being developed, it will cover strategies focused on quench pathogen quorum sensing (QS) systems, disassemble of bacterial functional membrane microdomains (FMMs), disruption of biofilm formation and bacterial toxin neutralization.

An Autoinducer Analogue Reveals an Alternative Mode of Ligand Binding for the LasR Quorum-Sensing Receptor

Bacteria use a cell-cell communication process called quorum sensing to coordinate collective behaviors. Quorum sensing relies on production and group-wide detection of extracellular signal molecules called autoinducers. Here, we probe the activity of the Pseudomonas aeruginosa LasR quorum-sensing receptor using synthetic agonists based on the structure of the native homoserine lactone autoinducer. The synthetic compounds range from low to high potency, and agonist activity tracks with the ability of the agonist to stabilize the LasR protein. Structural analyses of the LasR ligand binding domain complexed with representative synthetic agonists reveal two modes of ligand binding, one mimicking the canonical autoinducer binding arrangement, and the other with the lactone head group rotated approximately 150°. Iterative mutagenesis combined with chemical synthesis reveals the amino acid residues and the chemical moieties, respectively, that are key to enabling each mode of binding. Simultaneous alteration of LasR residues Thr75, Tyr93, and Ala127 converts low-potency compounds into high-potency compounds and converts ligands that are nearly inactive into low-potency compounds. These results show that the LasR binding pocket displays significant flexibility in accommodating different ligands. The ability of LasR to bind ligands in different conformations, and in so doing, alter their potency as agonists, could explain the difficulties that have been encountered in the development of competitive LasR inhibitors.

Dihydropyrrolones as bacterial quorum sensing inhibitors

Bacteria regulate their pathogenicity and biofilm formation through quorum sensing (QS), which is an intercellular communication system mediated by the binding of signaling molecules to QS receptors such as LasR. In this study, a range of dihydropyrrolone (DHP) analogues were synthesized via the lactone-lactam conversion of lactone intermediates. The synthesized compounds were tested for their ability to inhibit QS, biofilm formation and bacterial growth of Pseudomonas aeruginosa. The compounds were also docked into a LasR crystal structure to rationalize the observed structure-activity relationships. The most active compound identified in this study was compound 9i, which showed 63.1% QS inhibition of at 31.25 µM and 60% biofilm reduction at 250 µM with only moderate toxicity towards bacterial cell growth.

Design and Synthesis of Lactams Derived from Mucochloric and Mucobromic Acids as Pseudomonas aeruginosa Quorum Sensing Inhibitors

Bacterial infections, particularly hospital-acquired infections caused by Pseudomonas aeruginosa, have become a global threat with a high mortality rate. Gram-negative bacteria including P. aeruginosa employ N-acyl homoserine lactones (AHLs) as chemical signals to regulate the expression of pathogenic phenotypes through a mechanism called quorum sensing (QS). Recently, strategies targeting bacterial behaviour or QS have received great attention due to their ability to disarm rather than kill pathogenic bacteria, which lowers the evolutionary burden on bacteria and the risk of resistance development. In the present study, we report the design and synthesis of N-alkyl- and N-aryl 3,4 dichloro- and 3,4-dibromopyrrole-2-one derivatives through the reductive amination of mucochloric and mucobromic acid with aliphatic and aromatic amines. The quorum sensing inhibition (QSI) activity of the synthesized compounds was determined against a P. aeruginosa MH602 reporter strain. The phenolic compounds exhibited the best activity with 80% and 75% QSI at 250 µM and were comparable in activity to the positive control compound Fu-30. Computational docking studies performed using the LasR receptor protein of P. aeruginosa suggested the importance of hydrogen bonding and hydrophobic interactions for QSI.

Synthesis and biological evaluation of novel acyclic and cyclic glyoxamide based derivatives as bacterial quorum sensing and biofilm inhibitors

Bacteria regulate the expression of various virulence factors and processes such as biofilm formation through a chemically-mediated communication mechanism called quorum sensing. Bacterial biofilms contribute to antimicrobial resistance as they can protect bacteria embedded in their matrix from the effects of antibiotics. Thus, developing novel quorum sensing inhibitors, which can inhibit biofilm formation, is a viable strategy to combat antimicrobial resistance. We report herein the synthesis of novel acyclic and cyclic glyoxamide derivatives via ring-opening reactions of N-acylisatins. These compounds were evaluated for their quorum sensing inhibition activity against P. aeruginosa MH602 and E. coli MT102. Compounds 20, 21 and 30 displayed the greatest quorum sensing inhibition activity against P. aeruginosa MH602, with 71.5%, 71.5%, and 74% inhibition, respectively, at 250 μM. Compounds 18, 20 and 21 exhibited the greatest QSI activity against E. coli MT102, with 71.5%, 72.1% and 73.5% quorum sensing inhibition activity, respectively. In addition, the biofilm inhibition activity was also investigated against P. aeruginosa and E. coli at 250 μM. The glyoxamide compounds 16, 18 and 19 exhibited 71.2%, 66.9%, and 66.5% inhibition of P. aeruginosa biofilms, respectively; whereas compounds 12, 20, and 22 showed the greatest inhibitory activity against E. coli biofilms with 87.9%, 90.8% and 89.5%, respectively. Finally, the determination of the in vitro toxicity against human MRC-5 lung fibroblast cells revealed that these novel glyoxamide compounds are non-toxic to human cells.