Preparation Of Membrane-active Antimicrobial Agents And Research On Its Application In Construction Of Antimicrobial Surfaces

The bacterial infection caused by the implant materials in the clinical application has become an urgent problem to be solved.The construction of antibacterial surfaces is an effective way to solve this problem.The traditional antibacterial surfaces loaded with metal ions and antibiotics have obvious drawbacks,such as high cytotoxicity and the increased risk of bacterial resistance.Therefore,the preparation of novel antibacterial agents and their use in the construction of antibacterial surfaces have become a research hotspot in this field.Membrane-active antibacterial agents have received widespread attentions,because they have obvious advantages,including excellent antibacterial properties,good stability,and avoidance of drug resistance.In this study,we first developed a novel type of highly effective and low-toxic antibacterial agent,and then used the optimized antibacterial agent to construct the antibacterial surface of the implanted materials.This thesis mainly includes the following work:(1)Using the natural product ?-mangostin as the starting material,a series of ?-mangostin derivatives as small molecule-based antibacterial agents were designed and synthesized.The antibacterial and hemolytic activities as well as the structure-activity relationships of ?-mangostin derivatives were then studied.Finally,the candidate compound M3 with broad spectrum antibacterial activity was obtained.(2)A series of novel xanthone-based antimicrobial agents were designed and synthesized by using total synthesis method.First,the xanthone core is formed by one-step reaction from phloroglucinol and 2,4,6-trihydroxybenzoic acid.Then,the hydrophobic fatty chains and cationic moieties were respectively introduced to xanthone core,leading to the formation of the amphiphilic structures.The antibacterial and hemolytic activities as well as structure-activity relationships of xanthone derivatives were then explored.Finally,the candidate compounds X6 and X18 with potent antibacterial activity were obtained.(3)A series of flavone-based small molecules mimicking antimicrobial peptides were designed and synthesized,using the natural product icaritin as the starting material.The antibacterial and hemolytic activities as well as structure-activity relationships of flavone derivatives were then explored.Finally,the candidate compound F6 with potent antibacterial activity was obtained.(4)The candidate antimicrobial agents M3,X6,X18 and F6 were further studied.Their biological activities and mechanism of action were summarized as follows: M3 showed excellent and broad-spectrum activity against Gram-positive(MIC = 0.78-3.13 ?g/m L)and Gram-negative bacteria(MIC = 1.56-6.25 ?g/mL).X6,X18 and F6 showed excellent antibacterial activity against gram-positive bacteria(MIC = 0.78-3.13 ?g/mL).M3,X6,X18 and F6 killed bacteria rapidly by directly destroying the bacterial membranes.They have several advantages,including fast killing rate,low hemolytic toxicity,low cytotoxicity,high membrane selectivity and low probability of developing drug resistance.In addition,M3,X6 and F6 all maintained excellent antibacterial efficacy in a mouse model of corneal infection caused by MRSA.(5)X18 was selected as the best loaded antimicrobial agent for constructing the antimicrobial surface.In order to maintain the steric configuration and antibacterial properties of X18 and introduce azide groups,one of the arginines of X18 was replaced with an azide-containing PEG(8)chain to produce X28.X28 was successfully grafted onto the silicon surface by click reaction and silane coupling agent.The modified surface Si-X28 exhibits excellent antibacterial activity against both S.aureus and E.coli.It can rapidly kill bacteria by destroying their membranes,and has good biocompatibility.In summary,we successfully designed and synthesized a series of membrane-targeting xanthone-based or flavone-based small molecules as antimicrobial agents.They can solve the defects of ?-mangostin and icaritin as antimicrobial materials,and provide the ideal loaded antimicrobial agents for the construction of antibacterial surfaces.The selected antibacterial agent was then fixed on the surface of silicon to successfully construct a highly effective and low-toxic antibacterial surface,by using chemical grafting method.This strategy provides a promising approach for addressing the problems of the infections in biomedical materials.