Total synthesis of Met10-teixobactin

Discovery of the Lipopeptides Albubactins A-H from Streptomyces albidoflavus RKJM0023 via Chemical Elicitation with Rhamnolipids and Synthesis of Albubactin A

The marine tunicate-derived Streptomyces albidoflavus RKJM0023 was cultured in the presence of a rhamnolipid mixture in an effort to elicit the production of silent natural products. MS/MS-based molecular networking analysis enhanced with nonparametric statistics highlighted the upregulation of a molecular cluster (Kruskal-Wallis p = 1.6 e-6 for 1) in which no MS/MS features had library matches. Targeted isolation of these features resulted in the discovery of nine new N-acylated lipopeptides, albubactins A-H (1-8) each containing a unique glutamine tripeptide and a C-terminal ethyl ester moiety. Three related albubactin acids A-C (9-11) lacking the ethyl ester were also identified. NMR spectroscopy and UPLC-HR-ESI-MS/MS demonstrated that the albubactins were obtained as mixtures that shared a common m/z and differed only in their acylated terminal groups. Due to the complex spectroscopic elucidation with many overlapping shifts, a total synthesis of albubactin A (1) was completed and used to determine the absolute configuration of the new albubactins.

Discovery, synthesis, and optimization of teixobactin, a novel antibiotic without detectable bacterial resistance

Discovering new antibiotics with novel chemical scaffolds and antibacterial mechanisms presents a challenge for medicinal scientists worldwide as the ever-increasing bacterial resistance poses a serious threat to human health. A new cyclic peptide-based antibiotic termed teixobactin was discovered from a screen of uncultured soil bacteria through iChip technology in 2015. Teixobactin exhibits excellent antibacterial activity against all the tested gram-positive pathogens and Mycobacterium tuberculosis, including drug-resistant strains. Given that teixobactin targets the highly conserved lipid II and lipid III, which induces the simultaneous inhibition of both peptidoglycan and teichoic acid synthesis, the emergence of resistance is considered to be rather difficult. The novel structure, potent antibacterial activity, and highly conservative targets make teixobactin a promising lead compound for further antibiotic development. This review provides a comprehensive treatise on the advances of teixobactin in the areas of discovery processes, antibacterial activity, mechanisms of action, chemical synthesis, and structural optimizations. The synthetic methods for the key building block l-allo-End, natural teixobactin, representative teixobactin analogues, as well as the structure-activity relationship studies will be highlighted and discussed in details. Finally, some insights into new trends for the generation of novel teixobactin analogues and tips for future work and directions will be commented.

The Total Chemical Synthesis and Biological Evaluation of the Cationic Antimicrobial Peptides, Laterocidine and Brevicidine

Antimicrobial resistance is a significant threat to public health systems worldwide, prompting immediate attention to develop new therapeutic agents with novel mechanisms of action. Recently, two new cationic non-ribosomal peptides (CNRPs), laterocidine and brevicidine, were discovered from Brevibacillus laterosporus through a global genome-mining approach. Both laterocidine and brevicidine exhibit potent antimicrobial activity toward Gram-negative bacteria, including difficult-to-treat Pseudonomas aeruginosa and colistin-resistant Escherichia coli, and a low risk of resistance development. Herein, we report the first total syntheses of laterocidine and brevicidine via an efficient and high-yielding combination of solid-phase synthesis and solution-phase macrolactamization. The crucial depsipeptide bond of the macrolactone rings of laterocidine and brevicidine was established on-resin between the side-chain hydroxy group of Thr⁹ with Alloc-Gly-OH or Alloc-Ser(tBu)-OH, respectively. A conserved glycine residue within the lactone macrocycle is exploited for the initial immobilization onto the hyper acid-labile 2-chlorotrityl chloride resin, subsequently enabling an efficient solution-phase macrocyclization to yield laterocidine and brevicidine in 36% and 10% overall yields, respectively (with respect to resin loading). A biological evaluation against both Gram-positive and Gram-negative bacteria demonstrated that synthetic laterocidine and brevicidine possessed a potent and selective antimicrobial activity toward Gram-negative bacteria, in accordance with the isolated compounds.

Thiol-ene Enabled Chemical Synthesis of Truncated S-Lipidated Teixobactin Analogs

Herein is described the introduction of lipid moieties onto a simplified teixobactin pharmacophore using a modified Cysteine Lipidation on a Peptide or Amino acid (CLipPA) technique, whereby cysteine was substituted for 3-mercaptopropionic acid (3-MPA). A truncated teixobactin analog was prepared with the requisite thiol handle, thus enabling an array of vinyl esters to be conveniently conjugated onto the simplified teixobactin pharmacophore to yield S-lipidated cyclic lipopeptides.

Teixobactin: A Paving Stone toward a New Class of Antibiotics?

Antimicrobial resistance is a serious threat to human health worldwide, prompting research efforts on a massive scale in search of novel antibiotics to fill an urgent need for a remedy. Teixobactin, a macrocyclic depsipeptide natural product, isolated from uncultured bacteria (Eleftheria terrae), displayed potent activity against several Gram-positive pathogenic bacteria. The distinct pharmacological profile and interesting structural features of teixobactin with nonstandard amino acid (three d-amino acids and l-allo-enduracididine) residues attracted several research groups to work on this target molecule in search of novel antibiotics with new mechanism. Herein, we present a comprehensive and critical perspective on immense possibilities offered by teixobactin in the domain of drug discovery. Efforts made by various research groups since its isolation are discussed, highlighting the molecule's considerable potential with special emphasis on replacement of amino acids. Critical analysis of synthetic efforts, SAR studies, and the way forward are provided hereunder.