To cope with the global bacterial multidrug resistance, scientific communities have devoted significant efforts to develop novel antibiotics, particularly those with new modes of actions. Teixobactin, recently isolated from uncultured bacteria, is considered as a promising first-in-class drug candidate for clinical development. Herein, we report its total synthesis by a highly convergent Ser ligation approach and this strategy allows us to prepare several analogues of the natural product.

No abstract

A convergent synthesis via the late-stage serine ligation of naturally occurring calcium-dependent antibiotic CDA3a and its analogues has been developed, which allowed us to readily synthesize the analogues with the variation on the lipid tail. Some analogues were found to show 100–500-fold higher antimicrobial activity than the natural compound CDA3a against drug resistant bacteria. This study will enhance our understanding of CDA3a and provide valuable antibacterial lead candidates for further development.

Convergent Ser/Thr ligation has been used to prepare a series of teixobactin analogues (28 in total) to establish a structure-activity relationship of teixobactin. anti-bacterial evaluations of these synthetic analogues have revealed the critical amino acid residues and the sites tolerable of modifications. These studies will shed lights on the further development of teixobactin analogues with improved antibacterial activities.

Daptomycin is effective in treating infections caused by antibiotic-resistant Gram-positive pathogens, including methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococci (VRE), and vancomycin-resistant S. aureus (VRSA). Due to its distinct mechanism of action toward multidrug-resistant bacteria, daptomycin provides an attractive structural motif to generate new daptomycin-based antibiotics to combat the problem of bacterial resistance. In this study, we used the total synthesis method to produce daptomycin analogues with a variety in terms of types and sites of modifications. Five classes of daptomycin analogues were synthesized, and the antimicrobial activities of the analogues were analyzed by several biological assays. From this study, we established a comprehensive structure–activity relationship of daptomycin which will lay the foundation for the further development of daptomycin-based antibiotics.

The development of novel antibiotics is critical to combating the growing emergence of drug-resistant pathogens. Malacidin A is a new member of the calcium-dependent antibiotic (CDAs) family with activity against antibioticresistant pathogens. Its mode of action is distinct from classical CDAs. However, the absolute structure of malacidin A has not been established. Herein, the total syntheses of malacidin A and its analogues are reported by a combination of Fmocbased solid-phase peptide synthesis (SPPS) and b-hydroxyaspartic acid ligation-mediated peptide cyclization. The total synthesis enabled us to establish the absolute configuration of malacidin A, which is in agreement with those for natural malacidin A confirmed by advanced Marfeys analysis in our study.

Increased usage of daptomycin to treat infections caused by Gram-positive bacterial pathogens has resulted in emergence of resistant mutants. In a search for more effective daptomycin analogues through medicinal chemistry studies, we found that methylation at the nonproteinogenic amino acid kynurenine in daptomycin could result in significant enhancement of antibacterial activity. Termed "kynomycin," this new antibiotic exhibits higher antibacterial activity than daptomycin and is able to eradicate methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE) strains, including daptomycin-resistant strains. The improved antimicrobial activity of kynomycin was demonstrated in in vitro time-killing assay, in vivo wax worm model, and different mouse infection models. The increased antibacterial activity, improved pharmacokinetics, and lower cytotoxicity of kynomycin, compared to daptomycin, showed the promise of the future design and development of next-generation daptomycin-based antibiotics.

An aqueous dispersion of polyethylenimine-modified graphene oxide (PEI-GO) was prepared via a one-step synthesis through an epoxy ring-opening reaction. PEI-GO exhibited bacterial growth inhibition activity on methicillin-resistant Staphylococcus aureus (MRSA) with a minimum inhibitory concentration as low as 8 μg mL–1. Time–kill curve assay and SYTOX Green assay showed the antibacterial activity and bacteria cell membrane permeability of PEI-GO, respectively. Most importantly, when PEI-GO was employed at 1–2 μg mL–1, a synergistic effect with daptomycin to resensitize daptomycin-resistant MRSA was revealed. A synergistic effect between PEI-GO and daptomycin provides a possible way to increase bacterial killing and reduce the development of daptomycin resistance. The antibacterial activity of PEI-GO is attributed to the damaged cell membrane caused by the sharp edge and chain structure of the PEI-GO nanosheets as well as the high density of amine groups present in the PEI chains. Our results indicate that PEI-GO dispersion has a great potential for clinical pathogenic bacteria treatment.