Tryptophan-Based Structural Modification Of Daptomycin And Its Antibacterial Activity Evaluation

Bacterial infection is an important factor endangering global public health.Antibiotics have significantly contributed to the treatment of infectious diseases.However,due to the abuse of antibiotics,antimicrobial resistance has gradually become an urgent public health threat,which reduces the efficacy of antibiotics.The studies of previous antibiotics development suggest that making rational modifications to the key sites on the core backbone of antibiotics can contribute to develop a new antibiotic.Daptomycin has potent antibacterial activity against Gram-positive pathogens,and has unique mechanism of action and novel structure.Daptomycin has the potential to be derivatized to produce next-generation daptomycin-based antibiotics.Previous preparation of daptomycin analogues involves reconstruction of its backbone.The complex synthesis steps lead to high cost and low efficiency in constructing analogue libraries.This paper realized the accurate late modification of tryptophan site in daptomycina by improving the previous modification method and combining the team’s own technology,and tryptophin-modified daptomycin analogue library was constructed in a more efficient and convenient way.This approach greatly shortens the synthesis time and reduces the synthesis cost.In this paper,based on the structure-activity relationship of daptomycin,different phenyls were introduced into daptomycin through the tryptophan modification methods.The antibacterial activities of these analogues were evaluated,including the determination of minimal inhibitory concentration,hemolytic activity and serum stability.In the first part,aryl groups were introduced into the C-2 position of the indole of daptomycin tryptophan by the formation of C-C bonds and C-S bonds.A total of 39 analogues were obtained.We analyzed the effect of different aryl groups of tryptophan on the antibacterial activity of daptomycin.The results indicate that tryptophan is a key site to regulate the antimicrobial activity of daptomycin.We obtained a daptomycin analogue with improved antibacterial activity.Its hemolytic activity was less than 1%.It maintained good serum stability in vitro.It has potential to become a new generation antibiotic with more effective antibacterial activity,stable and safe.Bicyclic peptides increase the conformational stiffness,and have the advantages of better affinity and selectivity to target sites,higher metabolic stability,and better membrane permeability.In the second part,bicyclic analogues were constructed based on Trp1 and Orn6.The linker containing thiophenol was attached to the Orn6,and the intramolecular cyclizations were achieved by the radical addition reaction of thiophenol to tryptophan developed by our research group.Five bicyclic daptomycin analogues were obtained.Unfortunately,the minimal inhibitory concentration showed that the bicyclic analogues lost antibacterial activity.In summary,we used a more efficient and convenient method to obtain a variety of daptomycin analogues by introducing aryl into the C-2 position of indole on Trp1.By measuring the minimum inhibitory concentration,hemolytic activity and serum stability,we discussed the structure-activity relationship between tryptophan site substitution and daptomycin,screened out the analogues that are promising to develop the next generation of antibiotic.In this study,we also constructed bicyclic daptomycin analogues for the first time,which resulted in the loss of antibacterial activity,but enriched the structural diversity of daptomycin analogues.This study obtained an analogue with improved antibacterial activity,and provided a theoretical basis for the further modification of daptomycin and it has great significance for the development of the next generation of new daptomycin antibiotic.