Design,synthesis And Evaluation Of Biaromatic Pyrrolidone Derivatives As Quorum Sensing Inhibitors

The widespread application and abuse of antibiotics has led to varying degrees of bacterial resistance worldwide.At the same time,in the past two decades,studies of new drugs or lead compounds have been found greatly reduced.The shortage of antibacterial drugs has become an increasingly serious challenge for people.Quorum sensing is the process of communication between bacterial cells.Chemical signaling molecules in the quorum sensing process can directly or indirectly affect bacterial toxin production,protease activity and bacterial resistance.Blocking the connection among these cells can effectively reduce the toxicity and drug resistance of bacteria.In this paper,the results of previous studies on bromofuranone compounds and aryl-substituted furanone compounds were reviewed,then we replaced the bromine atom in furanone compounds with aromatic groups to investigate the effect of different substituents on their quorum sensing inhibitory activity.The change in quorum sensing inhibitory activity after conversion of the lactone ring to the lactam ring was also determined.Thus,arylaklyl furanones 7 and bromopyrrolidones 9,were designed to investigate the effects of different positions of the substituents on the benzene ring in the compound on pyocyanin production and protease activity.By determining the activity of these two series of compounds,we found a preferred modified structure to synthesize an aryl-pyrrolidone compound.The final results are as follows:For aryl furanone compounds,such compounds do not inhibit Gram-positive bacteria such as Bacillus subtilis,Staphylococcus aureus,methicillin-resistant Staphylococcus aureus,Staphylococcus epidermidis,Streptococcus pneumoniae and Gram-negative bacteria like Escherichia coli and Pseudomonas aeruginosa.Those compounds do not bring selective pressure to the growth of those bacteria.Some compounds such as 7a and 7g are relatively potent pyocyanin inhibitors.All of the compounds showed good protease inhibition activity,and the protease inhibition activity of compounds 7a,7f and 7g is optimal.In combination with pyocyanin inhibition and protease inhbition activity,it can be inferred that the 2’-substitution and 3’-substituted phenyl ring in the compounds can improve the quorum sensing inhibition effects of the compounds,and the methoxy,methyl and fluorine atoms are all active substituents.It is also worth noting that the quorum sensing inhibitory activity of the 4’-substituted aromatic ring is poor,presumably because the structure size of these compound exceeds the size of the protein cavity.As for those bromopyrrolidone compounds,inhibition activities can be quite First of all,such compounds have good antibacterial activity against Gram-positive bacteria such as Bacillus subtilis,Staphylococcus aureus,methicillin-resistant Staphylococcus aureus,Staphylococcus epidermidis,Streptococcus pneumoniae.The activity of the bacteria is comparable to that of ciprofloxacin.However,these compounds have no antibacterial activity against Gram-negative bacteria such as Escherichia coli and Pseudomonasaeruginosa,and do not inhibit the growth of Pseudomonas aeruginosa;although such compounds have certain inhibitory effects against pyocyanin expression in Pseudomonas aeruginosa,unfortunately no compound is a potent inhibitor,the best active compound 9d can inhibit 65.64%of the pyocyanin expression;such compounds showed moderate inhibitory activity against protease in Pseudomonas aeruginosa(proteolytic enzyme activity is about 40%of the blank control).Further,the preferred substituent groups on the N atom are n-hexyl group,benzyl group and tetrahydroindenyl group.It is speculated that the size of these groups is compatible with the volume of the protein cavity,and the hydrophobic interaction increases the affinity of the compound with the target.The arylpyrrolidone compounds are the most potential compounds synthesized in this subject.The results of biological activity assays show that these compounds has no inhibitory effect on Gram-positive bacteria such as Bacillus subtilis,Staphylococcus aureus,methicillin-resistant Staphylococcus aureus,Staphylococcus epidermidis,Streptococcus pneumoniae and Gram-negative bacteria like Escherichia coli and Pseudomonas aeruginosa.The inhibition activities(the pyocyanin production and protease activity in Pseudomonas aeruginosa)of the ortho-substituted phenyl ring pyrrolidone compounds are significantly better than that of the meta-and para-substituted compounds,we speculate the ortho-substituted compound molecular size is more suitable for the cavity structure of the target protein;compared to the previously reported arylpyrrolidone compounds,such compounds have a lower degree of inhibition on P.aeruginosa biofilm,we speculate that this is due to the complex cell wall of Gram-negative bacteria,the previously reported inhibitors were tested using Enterococcus faecalis(a Gram-positive bacterium),we hypothesize that the cell wall of P.aeruginosa can block the infiltration of excessive amounts of such compounds into cells;compound 10a is the compound with the best quorum sensing activity in this series of compounds.It is believed that this compound can provide good guidance for the development of quorum sensing inhibitors in the future.In summary,we have successfully designed and synthesized 29 novel quorum sensing inhibitors for the first three series of aryl furanone,bromo-pyrrolidone and arylpyrrolidone compounds.Through minimum inhibitory concentration assay,growth inhibition assay,pyocyanin expression assay,proteolytic activity assay,biofilm inhibition assay,and antibiotic combination experiments,we have found that arylpyrrolidone compounds exhibit excellent quorum sensing inhibitory activity.Thus we believe that(Z)-1-benzyl-5-(3-methylbenzylene)-4-(3-methylphenyl)-1,5-dihydro-2H-pyrrol-2-one(10a)is worth in-depth study,this compound could be conducted as a lead structure for novel quorum sensing inhibitors.