Synthesis, nanostructuring and in silico studies of a new imine bond containing a macroheterocycle as a promising PBP-2a non-ß-lactam inhibitor.

This study is devoted to the synthesis of a 40-membered macroheterocycle with its further nanostructuring by magnetite nanoparticles. The mentioned macroheterocycle was synthesized by the [2+2] cyclocondensation of the oxygen-containing diamine with an aromatic dialdehyde in a non-catalytic medium and with no work-up procedure. The structure of the obtained macroheterocycle was studied by 1H and 13C nuclear magnetic resonance spectroscopy and matrix-assisted laser desorption/ionization-time of flight mass spectrometry. Furthermore, the nanosupramolecular complex of macroheterocycles with magnetite nanoparticles was obtained and investigated by Fourier-transform infrared and ultraviolet-visible spectroscopy methods. Shifts in the infrared spectra of the nanosupramolecular complex indicate the interaction through metal-aromatic ring non-covalent bonding. The shift is also observed for the C-O-C stretching band of ether bonds. The loading rate of macroheterocycles on magnetite nanoparticles was 18.6%. The morphology of the ensemble was studied by transmission electron microscopy, which confirmed the synthesis of nanospherical particles with a diameter range of 10-20 nm. Powder X-ray diffraction analysis showed patterns of cubic Fe3O4 nanoparticles with a crystallite size equal to 9.1 nm. The macroheterocycle and its nanosupramolecular complex were tested against Klebsiella pneumoniae, Pseudomonas aeruginosa and Staphylococcus aureus. The results have shown that the created complex has shown 64 times better activity against Staphylococcus aureus in comparison with the individual macroheterocycle and 32 times better activity in comparison with the pristine antibiotic Ampicillin as a control. In addition, computational analysis of the macroheterocycle was performed at the B3LYP/6-31G level in water. Molecular docking analyses for the macroheterocycle revealed Penicillin-binding protein PBP2a (5M18) from the transpeptidase family as a target protein in Staphylococcus aureus.

Methodological tools to study species of the genus Burkholderia.

Bacteria belonging to the Burkholderia genus are extremely versatile and diverse. They can be environmental isolates, opportunistic pathogens in cystic fibrosis, immunocompromised or chronic granulomatous disease patients, or cause disease in healthy people (e.g., Burkholderia pseudomallei) or animals (as in the case of Burkholderia mallei). Since the genus was separated from the Pseudomonas one in the 1990s, the methodological tools to study and characterize these bacteria are evolving fast. Here we reviewed the techniques used in the last few years to update the taxonomy of the genus, to study gene functions and regulations, to deepen the knowledge on the drug resistance which characterizes these bacteria, and to elucidate their mechanisms to establish infections. The availability of these tools significantly impacts the quality of research on Burkholderia and the choice of the most appropriated is fundamental for a precise characterization of the species of interest.Key points• Updated techniques to study the genus Burkholderia were reviewed.• Taxonomy, genomics, assays, and animal models were described.• A comprehensive overview on recent advances in Burkholderia studies was made.

Synthesis, crystal structure and antibacterial studies of dihydropyrimidines and their regioselectively oxidized products.

The syntheses and investigations of new biologically active derivatives of dihydropyrimidines by Biginelli reaction in the presence of copper triflate are reported. Due to the fact that salicylaldehyde and its derivatives under Biginelli reaction conditions can lead to the formation of 2 types of dihydropyrimidines, the influence of copper triflate on product formation was also investigated. In addition to this, regioselective oxidation of dihydropyrimidines was performed in the presence of cerium ammonium nitrate and novel oxidized dihydropyrimidines were obtained. Single crystals of some of them were obtained and as a result, the structures of them were investigated by X-ray diffraction method, which allows determining the presence of hydrogen bonds in their structures. In addition to this, the presence of hydrogen bonds in their structures affects the formation of the corresponding tautomer during oxidizing of dihydropyrimidines. Since dihydropyrimidines are claimed to be biologically active compounds, activities of the synthesized compounds were studied against Acinetobacter baumanii, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae and Staphylococcus aureus bacteria.

Correction: Synthesis, crystal structure and antibacterial studies of dihydropyrimidines and their regioselectively oxidized products.

[This corrects the article DOI: 10.1039/D0RA10255E.].

Biochemical Characterization of Glutamate Racemase-A New Candidate Drug Target against Burkholderia cenocepacia Infections.

The greatest obstacle for the treatment of cystic fibrosis patients infected with the Burkholderia species is their intrinsic antibiotic resistance. For this reason, there is a need to develop new effective compounds. Glutamate racemase, an essential enzyme for the biosynthesis of the bacterial cell wall, is an excellent candidate target for the design of new antibacterial drugs. To this aim, we recombinantly produced and characterized glutamate racemase from Burkholderia cenocepacia J2315. From the screening of an in-house library of compounds, two Zn (II) and Mn (III) 1,3,5-triazapentadienate complexes were found to efficiently inhibit the glutamate racemase activity with IC50 values of 35.3 and 10.0 µM, respectively. Using multiple biochemical approaches, the metal complexes have been shown to affect the enzyme activity by binding to the enzyme-substrate complex and promoting the formation of an inhibited dimeric form of the enzyme. Our results corroborate the value of glutamate racemase as a good target for the development of novel inhibitors against Burkholderia.

Discovery of new diketopiperazines inhibiting Burkholderia cenocepacia quorum sensing in vitro and in vivo.

Burkholderia cenocepacia, an opportunistic respiratory pathogen particularly relevant for cystic fibrosis patients, is difficult to eradicate due to its high level of resistance to most clinically relevant antimicrobials. Consequently, the discovery of new antimicrobials as well as molecules capable of inhibiting its virulence is mandatory. In this regard quorum sensing (QS) represents a good target for anti-virulence therapies, as it has been linked to biofilm formation and is important for the production of several virulence factors, including proteases and siderophores. Here, we report the discovery of new diketopiperazine inhibitors of the B. cenocepacia acyl homoserine lactone synthase CepI, and report their anti-virulence properties. Out of ten different compounds assayed against recombinant CepI, four were effective inhibitors, with IC50 values in the micromolar range. The best compounds interfered with protease and siderophore production, as well as with biofilm formation, and showed good in vivo activity in a Caenorhabditis elegans infection model. These molecules were also tested in human cells and showed very low toxicity. Therefore, they could be considered for in vivo combined treatments with established or novel antimicrobials, to improve the current therapeutic strategies against B. cenocepacia.