Design,Synthesis And Antibacterial Evaluation Of 3-O-Aminoacyl-9-O-(2-chlorobenzyl) Oxime Clarithromycin Derivatives Against Drug-Resistant Bacteria

Compared with many other types of antibiotics,macrolide antibiotics have lots of extraordinary merits,such as broad-spectrum antibacterial property,significant curative effects,and no allergic reaction,etc,Since the 1950s,macrolide antibiotics have been widely used in the treatment of respiratory tract and soft tissue infections.However,due to the antibiotics abuse in clinical practice,the problem of bacterial resistance is becoming increasingly serious.Therefore,it is extremely urgent for us to research and develop the next generation of macrolide antibiotics.At present,the researchers have developed a large number of macrolide derivati-ves with excellent activity and low side effects through the structural modifications of macrolide antibiotics.The study of macrolide’s mechanism has shown that macrolide antibiotics can exert antibacterial activity by binding to bacterial ribosomes,blocking the extension of nascent peptides and further inhibiting protein synthesis.The oximation modification of the C-9 position of clarithromycin is considered to be one of the most potential structural modifications,which leads to 3-hydroxy-9-O-(2-chlorobenzyl)oxime clarithromycin that has been frequently reported as an important intermediate.Therefore,the intermediate was selected as a lead compound for further modification of the hydroxyl group at the C-3 position.The resultant target compounds could also interact with C2610,G2505 and C2611 via hydrophobic,hydrogen bond and stacking interactions,in addition to the essential binding sites such as A2058 and A2062.In particular,the introduced side chains could extend into the PTC region of bacterial ribosome to produce the second interactions,which could significantly improve the antibacterial activity.In this study,we took clarithromycin as the starting material to synthesize the key intermediate of 3-hydroxy-9-O-(2-chlorobenzyl)oxime clarithromycin and then introduced a variety of carbamate side chains to the C-3 position,with the purpose of investigating the effect of modifications of C-3 and C-9 positions on antibacterial activity.In the course of this research,we established a reasonable synthetic route with simpler procedures,milder reaction conditions,and higher yields.In sum,26 novel 3-O-aminoacyl-9-O-(2-chlorobenzyl)oxime clarithromycin derivatives were designed and synthesized,and their structures were confirmed by using MS and 1H NMR spectra.The antibactterial activity of all target compounds was determined by using broth microdilution method.Their results were as follows:Among all the experimental bacterial strains,the target compounds showed excellent activity against mefA-resistant Streptococcus pneumoniae A22072 and penicillin-resistant Staphylococcus aureus ATCC31007.For example,their activity against the mefA-resistant Streptococcus pneumonia A22072 was the MIC values of 0.12～2μg/mL.In particular,compounds 7a and 7q exerted the most potent activity with the MIC value of 0.12μg/mL,compound 7z with a MIC value of 0.25μg/mL and compounds 7b,7d,7f,7i,7p and 7u with a MIC value of 0.5μg/mL,which displayed 8-～32-fold better activity than azithromycin(MIC = 4μg/mL).In contrast,compounds 7f,7i,7p and 7z had the MIC value of 4μg/mL against penicillin-resistant Staphylococcus aureus ATCC31007,64-fold better than the references(MIC = 256 pg/mL).Besides,compounds 7a,7b,7f,7p and 7z also showed strong antibacterial activity(MIC=8μg/mL)against erythromycin-resistant Streptococcus pyogenes,32-fold more potent than the references(MIC = 256μg/mL).For sensitive Staphylococcus aureus ATCC25923,compounds 7b,7o,7p,7x and 7z had the same MIC value of 4μg/mL and other compounds had the MIC values varying from 8 to 16μg/mL.For sensitive Streptococcus pyogenes,compound 7z showed a MIC value of 0.5μg/mL and other compounds possessed the MIC values between 1～4μg/mL.Overall,for resistant bacterial strains,with the exception of methicillin-resistant Staphylococcus aureus(S.aureus ATCC29213),the target compounds showed comparable or significantly enhanced activity compared with clarithromycin,while for the sensitive bacterial strains,they exhibited weaker activity than clarithromycin.It was worth mentioning that,for the same bacterial strain,the antibacterial activity of all target compounds was much better than that of the key intermediate 3,which further indicated the validity and feasibility of the combined structural modifications of the C-3 and the C-9 positions of clarithromycin.Through analyzing the structures of these compounds and their antibacterial activity,the structure-activity relationships were summarized as follows:1)Combinative modifications at the C-3 and the C-9 positions could increase the antibacterial activity compared with single modification at the C-9 position,which led to binding of the target compound with multiple sites of bacterial ribosomes,thereby increasing the antibacterial activity,especially the activity against resistant bacteria;2)An appropriate length of the arylalkyl side chain could produce a favorable impact on the antibacterial activity;3)The aromatic side chains containing groups capable of forming hydrogen bonds could enhance the antibacterial activity;4)the positions of the substituted groups on the side chains seemed to have little effect on the antibacterial activity.Through this research,we got a number of novel compounds with excellent antibacterial activity,especially against resistant bacteria strains such as methicillin-resistant Staphylococcus aureus ATCC31007,erythromycin-resistant Streptococcus pyogenes,and mefA-resistant Streptococcus pneumoniae A22072.These compounds were considered to have great potential value.On the basis of this research,further optimization of the above compounds maybe find macrolide candidate drugs with more potent anti-resistant bacteria and broader antibacterial spectrum.