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Polyether ionophores are complex natural products capable of transporting cations across biological membranes. Many polyether ionophores possess potent antimicrobial activity and a few selected compounds have the ability to target aggressive cancer cells. Nevertheless, ionophore function is believed to be associated with idiosyncratic cellular toxicity and, consequently, human clinical development has not been pursued. Here, we demonstrate that structurally novel polyether ionophores can be efficiently constructed by recycling components of highly abundant polyethers to afford analogues with enhanced antibacterial selectivity compared to a panel of natural polyether ionophores. We used classic degradation reactions of the natural polyethers lasalocid and monensin and combined the resulting fragments with building blocks provided by total synthesis, including halogen-functionalized tetronic acids as cation-binding groups. Our results suggest that structural optimization of polyether ionophores is possible and that this area represents a potential opportunity for future methodological innovation. [Figure not available: see fulltext.].

The efrapeptin family of peptide antibiotics produced by the fungus Tolypocladium niveum, and the neo-efrapeptins from the fungus Geotrichum candidumare inhibitors of F(1)-ATPase with promising antitumor, antimalaria, and insecticidal activity. They are rich in C(α)-dialkyl amino acids (Aib, Iva, Acc) and contain one β-alanine and several pipecolic acid residues. The C-terminus bears an unusual heterocyclic cationic cap. The efrapeptins C-G and three analogues of efrapeptin C were synthesized using α-azido carboxylic acids as masked amino acid derivatives. All compounds display inhibitory activity toward F(1)-ATPase. The conformation in solution of the peptides was investigated with electronic CD spectroscopy, FT-IR spectroscopy, and VCD spectroscopy. All efrapeptins and most efrapeptin analogues were shown to adopt helical conformations in solution. In the case of efrapeptin C, VCD spectra proved that a 3(10)-helix prevails. In addition, efrapeptin C was conformationally studied in detail with NMR and molecular modeling. Besides NOE distance restraints, residual dipolar couplings (RDC) observed upon partial alignment with stretched PDMS gels were used for the conformational analysis and confirmed the 3(10)-helical conformation.

International audience; An improved synthesis of n-octyl β-D-galactofuranoside was described using micro-wave activation. The resulting alkyl furanoside showed antibacterial activity against Mycobacterium smegmatis, a non-pathogenic model of Mycobacterium tuberculosis. It was further incorporated into a biodegradable PBAT/sodium caseinate polymer. The resulting biomaterial loaded with 5% of the pharmacophore retained the mycobacteriostatic properties and developed a mycobactericidal activity on contact and at the periphery of the film.

A chemical synthesis platform with broad applications and flexibility was rationally designed to inhibit biogenesis of adhesive pili assembled by the chaperone–usher pathway in Gram-negative pathogens. The activity of a family of bicyclic 2-pyridones, termed pilicides, was evaluated in two different pilus biogenesis systems in uropathogenic Escherichia coli . Hemagglutination mediated by either type 1 or P pili, adherence to bladder cells, and biofilm formation mediated by type 1 pili were all reduced by ≈90% in laboratory and clinical E. coli strains. The structure of the pilicide bound to the P pilus chaperone PapD revealed that the pilicide bound to the surface of the chaperone known to interact with the usher, the outer-membrane assembly platform where pili are assembled. Point mutations in the pilicide-binding site dramatically reduced pilus formation but did not block the ability of PapD to bind subunits and mediate their folding. Surface plasmon resonance experiments confirmed that the pilicide interfered with the binding of chaperone–subunit complexes to the usher. These pilicides thus target key virulence factors in pathogenic bacteria and represent a promising proof of concept for developing drugs that function by targeting virulence factors.