Design,Synthesis And Antibacterial Evaluation Of Novel Pleuromutilin Derivatives Possessing Secondary Amine Linker

Due to the longterm and large-scale application of antibiotics,bacterial resistance problem became an increasingly pressing problem in our country veterinary clinic.it was becoming harder to treat the growing number of infections,such as livestock and poultry respiratory diseases caused by drug-resistant Streptococcus suis,Mycoplasma gallisepticum,Mycoplasma bovis,avian Mycoplasma etc,animal intestinal infectious diseases caused by E.coli and Salmonella so on,as the antibiotics used to treat them become less effective in veterinary clinic.A series of problems caused by bacteria resistance:the available antibiotics become scarcer on clinic and the increase of medical costs,huge economic loss and so on.Especially in the mode of large-scale farming where the output cycle was getting shorter and shorter,when undergoing epidemic diseases caused by antibiotic-resistant bacteria,it may be impossible to control the epidemic and have to resort to elimination therapy,but this will cause huge impact on the aquaculture industry.Therefore,it was particularly important for ensuring the healthy development of livestock and poultry husbandry to promote the exploitation of animal-specific antibacterial drugs.Kavanagh's team separated a natural product,namely pleuromutilin,from Pleurotus mutilis and Pleurotus passeckeranius in 1951,and it exhibited modest antimicrobial activity.This kind of antibiotics had bacteriostatic action for most gram positive coccus and a small number of gram-negative fastidious bacteria such as haemophilus influenza,moraxella catarrhalis.Further research showed that it was not only active against penicillin-resistant and streptomycin-resistant staphylococci,but also highly active against Mycoplasma spp.Structure modification on the C14 side chain can obtain derivatives possessing good antibacterial efficacy such as three new drugs of pleuromutilins BC-3205,BC-3781,BC-7013 which were still in the stage of clinical research.So pleuromutilins are worth researching highly.In view of the predecessor research on the modifications in the C14 side chain o f pleuromutilin,a series of pleuromutilin derivatives possessing alkaline secondary amine were designed and synthesised through modifications in the C14 side chain.Target compounds were purified by column chromatography separation.The compound structure was confirmed with FT-IR,HR-MS,¹H NMR and ¹³C NMR.Broth micro dilution method was applied to pleuromutilin derivatives 1-13 for the determination of minimal inhibitory concentration?MIC?against methicillin-resistant Staphylococcus aureus?MRSA?ATCC 43300,S.aureus ATCC 29213,and clinical strains of S.aureus N9 respectively.Except MICs of compound 7,9,10 and 11 against the selected strains are>64?g/mL,the remaining compounds 1⁶,8,12,13 of MRSA ATCC 43300,S.aureus ATCC 29213,clinical strains of S.aureus N9 minimum bacteriostatic concentration were 0.25¹?g/mL,0.5⁴?g/mL,0.5⁴?g/mL.The results showed that the compound 8and Tiamulin shared the same antibacterial efficacy.Based on the measured MICs,0MIC,2MIC,8MIC,32MIC series concentration was selected in time-killing curve experiment against MRSA ATCC43300.According to the time-kill curves,the bacteria killed by most compounds in a time-dependent manner and compound 4,6,8,12,13 can achieve bactericidal effect with 8MIC,but the bactericidal rate was relatively slow,compound 4 can achieve bactericidal effect with 2MIC within 24 h.A preliminary investigation on the logarithm of Octanol-water partition coefficients of the compounds was conducted to evaluate their drug-likeness.Online ACD/Lab?Advanced Chemistry Development/Laboratory?version 5.0 software was adopted for predicating the calculated logarithm of Octanol-water partition coefficients?ClogP?of compounds,and with Tiamulin as a comparison.The results showed that Compound 12 got a lowest ClogP value,which indicated it may possess a better vivo pharmacokinetics.Compound 8possessed equivalent antibacterial activities to Tiamulin and a lower ClogP value than Tiamulin,which indicated that compound 8 was promising to develop further pharmacodynamic studies as a lead compound for animal-specific antimicrobial raw material.