Design,Synthesis And Antibacterial Evaluation Of 11-O-Aralkylcarbamoyl-3-O-descladinosylclarithromycin Derivatives

Macrolide antibiotics are lipophilic macrolactone ring compounds with weak alkalinity produced by Streptomycetes,to the macrolactone ring of which one or more deoxy sugars,usually cladinose or desosamine,are attached.Macrolide antibiotics have been widely used for the treatment of respiratory tract and soft tissue infections because of their broad antibacterial spectrum,few side effects and remarkable curative effects.However,the abuse of macrolide antibiotics has led to the growing number of drug-resistant bacteria,which weakens the effectiveness of macrolide antibiotics and severely limits their clinical use.Therefore,the research and development of new potent macrolide antibiotics against resistant bacteria have become the key problems to be solved urgently.The study of the antibacterial mechanism has indicated that macrolides can bind to the peptide release channel of the peptidyl transferase center in SOS subunit of bacterial ribosome,which can interfere the elongation of nascent peptide chain,so that they restrain the synthesis of protein,thereby showing antibacterial activity.The major mechanisms of bacterial resistance are the erm gene-mediated specific monomethylation or dimethylation of bacterial ribosome base and the mef gene-mediated efflux pump.The structural modification of macrolide antibiotics is a hot spot of current research and has become an effective way to find new drugs against resistant bacteria.However,there are few studies on the structural modification of the C-11 position of clarithromycin.Only EP-1553 obtained through the introduction of the C-11 side chain to clarithromycin has been reported.The aralkyl side chain at the C-11 position can bind with the hairpin structure of A752 in 23 S rRNA domain II,thereby enhancing the antibacterial activity.In addition,X-ray co-crystal structure study has showed that the 3-O-cladinose is not an essential part for macrolide antibiotics to exert antimicrobial activity.On the contrary,it can induce mef-gene expression,producing efflux pump resistance.Revomal of the 3-O-cladinose and oxidation of the C-3-OH or esterification of the C-3-OH give ketolides and acylides,respectively.They have been the third-generation macrolide antibiotics with potent activity against resistant Streptococcus pneumonia.In view of the research results above,we jointly modified the C-3 and C-11 positions of clarithromycin which was used as the mother nucleus.We designed and synthesized a total of 46 11-O-aralkylcarbamoyl-3-O-descladinosylclarithromycin derivatives in four series and confirmed their structures by MS,1H NMR and 13C NMR spectra.We also set up several simple and efficient synthetic routes that were characterized by the mild reaction conditions,the simple operations and the high yields.In this paper,the double-drop concentration dilution method was used to evaluate the in vitro antibacterial activity of the target compounds against five sensitive bacteria and five resistant bacteria.And clarithromycin and azithromycin were used as the control drugs.The results of the antibacterial activity were as follows:1)Anti-sensitive bacteria activity:Most of the target compounds showed excellent antibacterial activity against susceptible Streptococcus pyogenes,among which,the active compounds were D1,D2 and D3 with the MIC?0.03 ?g/mL.The target compounds showed good activity against Bacillus subtilis,and the best compound is A3(MIC = 0.25 Lg/mL).The target compounds exhibited activity against susceptible Staphylococcus aureus with the MIC value of 1 ?g/mL,slightly weaker than the control drugs.As for Escherichia coli and Pseudomonas aeruginosa,however,the activity of all the target compounds was weak,with MIC value of only 64 ?g/mL.2)Anti-resistant bacteria activity:Most of the target compounds showed excellent antibacterial activity against the mefA resistant phenotype Streptococcus pneumoniae,among which,A3,A12,A13,B3,C5,D1,D2 and D3 showed the MIC value of 0.5 ?g/mL,4-8 times better than those of the control drugs.The active compound against the ermB resistant phenotype Streptococcus pneumoniae was D3(MIC = 16 ?g/mL),showing 8-fold more potent activity than the control drugs(MIC>128 pg/mL).For the mefA+ ermB resistant phenotype Streptococcus pneumoniae,D2 and D3 had the MIC value of 4 ?g/mL,32-fold better than the control drugs(MIC =128 ?g/mL).For methicillin-resistant Staphylococcus aureus,the best compounds were B12 and C4 with the MIC value of 16 ?g/mL,displaying a 8-fold increase in antibacterial activity over the control drugs(MIC>128 ?g/mL).The most active compounds against resistant Streptcoccus yogenes were D4 and D8 with the MIC value of 32 ?g/mL,exerting a 4-fold increased activity over the control drugs(MIC>128 ?g/mL).Through the analysis of the relationship of the structures and antibacterial activity of A-D series,their structure-activity relationships were concluded as follows:1)Combinative modification of the C-3 and C-ll positions of clarithromycin could improve the antibacterial activity,especially the activity of anti-resistant bacteria.2)Compounds,bearing the side chain with a 6 atoms distance from the C-11 oxygen atom to the terminal aromatic ring,showed more potent antibacterial activity than that of those possessing the side chain with a 8 atoms distance.3)The compounds linking via propynylamide groups were more active than the compounds linking via acrylamide groups.4)The introduction of the strong electron-withdrawing groups or multi-substitutions on the terminal aromatic ring of the C-11 side chain was beneficial to enhance the antibacterial activity,while the introduction of the electron-donating groups on the terminal aromatic ring reduced the antibacterial activity.Besides,the positions of the substituents on the terminal aromatic ring had little effect on antibacterial activity.5)Possessing the same C-11 side chains,the compounds with the C-3-pyridyl acetate group at the C-3 position displayed more potent activity against both sensitive and resistant bacteria than the compounds with the C-3 ketone group.Furthermore,the compound obtained by the oxidation of C-3 hydroxyl group to the C-3 ketone and dehydration at the C-10,11 position lost its antibacterial activity.In conclusion,based on the antibacterial mechanism,resistance mechanisms,structure-activity relationships and previous studies of our group,we jointly modified the C-3 and C-11 positions of clarithromycin which was used as the mother nucleus.We designed and synthesized a total of 4611-O-aralkylcarbamoyl-3-O-descladinosylclarithromycin derivatives in four series,and then carried out the in vitro antibacterial activity evaluation.The results showed that D2 and D3,the compounds with the strongest antibacterial activity,exhibited outstanding antibacterial activity against susceptible Streptococcus pyogenes,susceptible Staphylococcus aureus,Bacillus subtilis,mefA resistant phenotype Streptococcus pneumoniae and mefA + ermB resistant phenotype Streptococcus pneumoniae.By means of further structural optimization on the basis of the two compounds,which can be used as broad-spectrum and high-potency lead compounds,it is expected to investigate macrolide candidate drugs with more potent antibacterial activity and broader antibacterial spectrum.The combinative structure modification of the C-3 and C-11 positions was first investigated by our group,not previously reported in the literature.This research not only obtained some macrolide derivatives with novel structures and outstanding antibacterial activity,but also provided a new direction for the structural modification of macrolide antibiotics.In addition,the structure-activity relationships analysis laid a theoretical foundation for the rational design of macrolide antibiotics.