Design, Synthesis And Biological Evaluation Of Antagonists Of Bacterial Quorum Sensing

In the process of the growth of bacteria, they can produce some small signalmolecules as a special language of communication and release them to the environment.When the signal molecules’ concentration reaches to a certain threshold, the expression ofrelated genes in bacteria will express to adapt to the change of the environment, which isknown as the bacterial quorum sensing （QS）.As the bacterial density increases, secreted signaling molecules achieve a certainconcentration, and they would combine with the corresponding receptor proteins in cellsto form a receptor protein signaling molecule polymer, and combine with the specificDNA sequence of chromosome, which causes expression of the target gene that controlssignal molecules’ synthesis, and then biological characteristics are produced. At the sametime, it generates much more signal molecules. Through quorum sensing, bacteria canregulate the expression of some gene within groups, such as the generation of antibioticproduction, pigment, bioluminescent, biofilm formation, the Ti plasmid transfer joint,toxicity gene expression, the swarm of bacteria and nitrogen fixation gene regulation, etc.In the late1970s, scientists discovered that natural or synthetic quorum-sensing regulatorcan interfere with quorum-sensing system signal to induce or inhibit some adverse geneexpression.Quorum sensing inhibitors don’t interfere with the normal physiological function ofbacterial cells in vivo, so it is regarded as a new direction of development of theantimicrobial drugs. The purpose of this topic is to synthesize a new type of quorumsensing inhibitors, which can be used for the treatment of diseases caused bygram-negative bacteria, especially resistant gram-negative bacteria. Of all the bacterialquorum sensing inhibitors, the AHL analogues, which inhibit QS system mediated with N-acylhomoserine lactones （AHLs） molecules, attracted the most attention and wasthought as the most effective inhibitors against gram-negative bacteria. So the target ofour project is to find high inhibitory activity of the gram-negative bacteria quorumsensing.Chromobacterium violaceum, a soilborne gram-negative bacterium whichsynthesizes the violet pigment violacein as a result of quorum sensing using itsautoinducer N-hexanoyl homoserine lactone （C₆-HSL）. Chromobacterium violaceumCV026as bacterial model had been widely applied to QS inhibitors research. A lot ofnovel N-acylhomoserine lactone derivatives had been developed in succession asinhibition of violacein production. C10-HSL and CL were the very effective quorumsensing inhibitors against violacein production among these derivatives. They includedhydrophilic homoserine lactone ring and hydrophobic alky group or aryl group, so theycould access to cell membrane freely. It is reported that homoserine lactone ring and acyltail lengths was important for QS inhibitor activity. When acyl tail chain is longer thaneight carbon atom, the compound would possess inhibitor activity.We designed two types of compounds. First of all, in order to prompt the activity,the homoserine lactone nucleus was reserved, benzenesulfonyl was introduced betweennucleus and amide group, owing to sulfonamides showing widespread biological activity.The benzene ring could increased hydrophobic and carbon length. In order to examinethe effect of tail alky group and aryl group to the QS inhibitor activity afterbenzenesulfonyl introduced, a series of novel compounds N-acylhomoserine lactonederivatives7a-7k were designed and synthesized as inhibitors. Moreover, the parentnucleus of homoserine lactone was replaced with3-amino-2-oxazolidinone, and toexplore the alkyl chain length’s influence on QS system inhibitory activity, we designedand synthesized a series of3-amino-2-oxazolidinone derivatives13a-13e. All the targetcompounds were evaluated as quorum sensing inhibitors by inhibition of violaceinproduction and a preliminary SARs study of these compounds was discussed. Starting from the simple and accessible raw materials, through9synthetic routesand multistep reactions,16target compounds were finally synthesized: according to thefirst scheme eleven compounds were synthesized; according to the second scheme fivecompounds were synthesized. And violacein inhibitory activity of the QS system inChromobacterium violaceum CV026was evaluated, including eight compounds whichhad inhibitory effect. Analysis of structure-activity relationship showed thatN-acylhomoserine lactone compounds with aryl groups substituted in side chaindisplayed better inhibitory activity than those substituted by alky groups on the sameposition and the length of alky chain should be no more than9carbon atoms. Furtheranalysis of aryl groups revealed that ortho substituted aryl group with electrophilicgroups were superior to para and meta substituted aryl group. Particularly, compounds7d with ortho substituted aryl group with halogen on side chain showed the highestinhibitory potency than other analogues.3-amino-2-oxazolidinone compounds hadinhibitory activity when the length of side chain is10. The next step of work is tooptimize the structure of7d, to explore QS system inhibitors with higher activity. Ourwork also provides reference for inhibitor synthesis of bacteria QS system in the future.