Design, Synthesis And Antibacterial Evaluation Of Clarithromycin Derivatives Against Resistant Bacteria

Macrolide antibiotic, a kind of weak alkaline lipophilic antibiotic produced by Streptomyces, has been commonly used for the treatment of respiratory tract infections in the early1950s because of its favorable antibacterial activity, spread antibacterial spectrum and tolerance. However, intensive emergence of the resistance to various antimicrobials severely affect therapeutic efficacy of the macrolides. It is a hot research to develop semi-synthetic derivatives of macrolides with low toxicity and potent activity.Macrolides inhibit protein synthesis by binding to the the bacterial ribosome, blocking the egress of nascent polypeptides. Based on previous research,we designed and synthesized the C-4"carbamates (A and B series,25compounds in all). While the amide groups at the side chain of C-4"carbamates can enhance affinity the hydrogen bond interaction for the PTC region, the aryl group can interact with the PTC region by π-stacking.Furthermore, we designed and synthesized the C and D series (15compounds in all) through consulting the structure of acylides with bioisosterism to overcome the deficiencies of clarithromycin in drug-resistant bacteria. In addition, we established the preparation,separation and purification methods of C-4"and C-3carbamates based on the explore of the synthesis route. Afterwards, we evaluated the in vitro activity by broth microdilution method, which was shown below.1) Antibacterial activity against susceptible strainsAll of the compounds have better activity against susceptible strains than the intermediates. Most of the compounds of B series can maintain the activity of clarithromycin against susceptible S.pneumoniae and S.aureus (0.03μg/ml≤MIC≤1μg/ml), the activity of the compounds of A, B series are comparable to the clarithromycin (0.007μg/ml<MIC≤0.25μg/ml), the MIC values of the compounds of C, D series are comparable to the intermediates (1μg/ml≤MIC≤16μg/ml);B15～B18have the best activity against susceptible strains. The MICs of B15, B18against susceptible S.pneumoniae are0.03μg/ml, the MICs of A6, B4, B5, B7-B18are comparable to clarithromycin (MIC≤0.5μg/ml);The MICs of B16, B18against susceptible S.aureus are0.03μg/ml, A3, A6, B4, B5, B7, B9, B11, B12, B15-B18can maintain the activity of clarithromycin against susceptible S.aureus (MIC≤0.5μg/ml); The MICs of B16and B17against susceptible S.pyogenes are0.015μg/ml and0.007μg/ml respectively, which are better than clarithromycin;2) Antibacterial activity against resistant strainsAll of the compounds showed significantly enhanced activity against three resistant S.pneumoniae strains compared to clarithromycin, which have comparable activity to clarithromycin against resistant S.pyogenes. B15to B18have good activity against resistant S.aureus (methicillin-resistant strain and penicillin-resistant strain). The anti-resistant strains activity of compounds of A, B series are better than the compounds of C, D series.B18showed the best activity against S.pneumoniae (ermB), which showed256fold better activity than the parent durgs. The compounds of A, B series, C1, C6-C8, D4and D6showed good activity against S.pneumoniae(ermB)(MIC≤64μg/ml); A3, A6, B17which have the best anti-resistant strains activity showed good activity against S.pneumoniae (mefA), the activity of above compounds showed256folds better activity than the parent durgs. B16even showed512fold better activity than the parent durgs. The activity of all of the compounds showed better activity than clarithromycin except D2, D3, D7(MIC8μg/ml). B18has the best anti--resistant S.pneumoniae (ermB+mefA) activity (MIC0.5μg/ml), which512fold better than clarithromycin(MIC128μg/ml). Most of the compounds of C and D series can maintain the activity of clarithromycin against three resistant S. pneumoniae.B15to B18showed better activity than other compounds against S.aureus (methicillin-resistant strain and penicillin-resistant strain), which are equal to the activity of clarithromycin.We summarized the structure-activity relationship as follows:1) The impact of teminal aryl groups of C-4"and C-3side chain on the activity: Firstly, the size of aryl groups can affect the antibacterial activity. The antibacterial activity against susceptible strains of compounds which have H or F substituted are better than the OCH3substituted compounds; while the compounds which have H or F substituted have worse activity against resistant strains; Secondly, the activity of p-substituents and m-substituents better than the o-substituents, the activity of the aryl group which no substituents better than the the aryl group with substituents. Thirdly, the compounds of nitro substituted showed better activity than the other compounds of non nitro group.2) The antibacterial activity of C-4" carbamates better than the C-3carbamates. We can refer that, the electronic effect and polarity of the side chain can affect the binding sites to the target, thereby affect the antibacterial activity.