Design And Synthesis Of Cyclo(L-Trp-L-Se) Derivatives And Study Of Antibacterial Activity

The introduction of penicillin in 1929 brought good news to human and animal health.However,the continued emergence of multi-drug resistant bacteria has rendered antibiotics ineffective and has the potential to cause global public health events.Therefore,there is an urgent need to search for new ways to treat human diseases that are less susceptible to bacterial resistance.Bacterial Quorum Sensing（QS）is a way for bacteria to transmit signals to each other through a medium.Bacteria produce Auto-inducers（AI）,which initiate the expression of related genes,such as bacterial biofilm,virulence factors,etc.,when the auto-inducer reaches a certain threshold,and the expression of related genes is regulated by the QS system.Therefore,we can block the production of Auto-inducers substances,or prevent the Auto-inducers substances from binding to the receptor,thus blocking the population-sensing signaling pathway and interfering with the expression of related genes.This new pathway does not act directly on the bacteria,so the bacteria will not develop drug resistance.For a long time,there are many small molecules called quorum sensing inhibitors（QSIs）,such as solenopsin A,cyclo（Trp-Ser）,cyclo（Gly-Gly）,etc.,which can block the quorum sensing signaling pathway.As one of quorum sensing inhibitors,cyclo（Trp-Ser）not only has structural rigidity,enzyme stability and strong self-assembly ability like other cyclic dipeptides,but also has an easily modified hydroxyl group.The natural cyclo（Trp-Ser）suffers from low anti-QS activity and poor water solubility,and we decided to modify its structure in order to improve its activity.In this paper,the hydroxyl group of the side chain of cyclo（L-Trp-L-Ser）is used to link the monosaccharide and the alkyl chain in the side chain to obtain cyclo（L-Trp-L-Ser）derivatives.Good glycosylated derivatives are evaluated for biological activity and biocompatibility,which lays the foundation for future clinical treatments.The main contents are as follows:Firstly,we attached monosaccharides and alkyl chains to the side chains of cyclo（L-Trp-L-Ser）to obtain two glycosylated and three alkylated derivatives,which laid the foundation for later experiments to evaluate the anti-QS ability of the derivatives.All derivatives were characterized using mass spectrometry,nuclear magnetic resonance spectrometry,and Fourier transform infrared spectroscopy,and the test results showed that the target products were successfully synthesized.Secondly,the anti-QS activity of c（WS）with glycosylated derivatives was evaluated.Pseudomonas aeruginosa PAO1 was used as the experimental strain,and the experimental concentration was appropriately adjusted based on the experimental concentration of natural cyclo（Trp-Ser）against QS of 1 mM,and their biological activity was evaluated based on this concentration.The experimental results showed that the two derivatives showed significant improvements in biofilm formation and clearance,chlorophyll,elastase,iron carriers,bacterial adhesion to the glass substrate and to cells compared to c（WS）.Meanwhile,the two derivatives were found to affect mainly the rhlR and rhlI systems of PAO1 by fluorescence quantitative PCR,and c（WS）-galactose was found to specifically recognize Lec A protein by isothermal quantitative thermal titration.Finally,the biocompatibility of the two derivatives was further evaluated based on the results of the assessment of their anti-QS ability.The final experimental results show that these two derivatives have a hemolysis value of sheep blood less than half hemolysis value(HC₅₀)at a concentration far greater than the maximum anti-QS experimental concentration,and have basically no cytotoxicity to cell A549,and are relatively stable in rabbit plasma.At the same time,we also tried to explore the combined bactericidal efficiency of these two derivatives with the traditional antibiotic Azithromycin（AZM）.Finally,it was found that these two derivatives can significantly improve the bactericidal efficiency of Azithromycin.