A novel synthetic method for backbone-cyclized polypeptide POL7080 with the help of hydrophobic-support materials.

Murepavadin (POL7080) in phase III clinical trials, a backbone-cyclized polypeptide composed of 14 amino acids, has a novel mode of action and shows a specific and efficient bactericidal effect against multidrug-resistant Pseudomonas aeruginosa. It is a potential candidate to treat severe P. aeruginosa infections in the future and still has significant commercial value for further research and development. In this paper, we report a liquid-phase peptide synthetic route for this valuable candidate polypeptide assisted by hydrophobic-support materials (tags), which overcomes the difficulties of high cost and poor yield in the traditional solid-phase synthesis of macrocyclic peptides. Through the careful optimization of reaction conditions and the innovative strategy of synthetic post-treatment, we established a simple and efficient liquid-phase synthetic route suitable for POL7080 and other similar structures, with satisfactory yield, high purity and a production process not being controlled by scale.

Design and Synthesis of 4-Fluorophenyl-5-methylene-2(5H)-furanone Derivatives as Potent Quorum Sensing Inhibitors.

Quorum sensing inhibitors (QSIs) are a class of compounds that can reduce the pathogenicity of bacteria without affecting bacterial growth. In this study, we designed and synthesized four series of 4-fluorophenyl-5-methylene-2(5H)-furanone derivatives and evaluated their QSI activities. Among them, compound 23e not only showed excellent inhibitory activity against various virulence factors but also significantly enhanced the inhibitory activity of antibiotics ciprofloxacin and clarithromycin against two strains of Pseudomonas aeruginosa in vitro. What is even more exciting is that it remarkably increased the antibacterial effect in vivo in combination with ciprofloxacin in the bacteremia model infected with P. aeruginosa PAO1. Moreover, 23e had little hemolytic activity to mouse erythrocytes. Further, the results of GFP reporter fluorescence strain inhibition and ß-galactosidase activity inhibition experiments demonstrated that 23e simultaneously targeted the three quorum sensing systems in P. aeruginosa. As a result, compound 23e could be used as an effective QSI for further development against bacterial infections.

Design, synthesis and evaluation of oxazolopyridinone derivatives as quorum sensing inhibitors.

The antibiotic crisis is associated with the appearance of multidrug resistant (MDR) pathogens, which has caused severe bacterial infections and imposed a huge burden on modern society. Therefore, there is an urgent need to develop new antibacterial drugs with novel mechanism of action. Here we designed and synthesized three series of benzoxazolone, oxazolopyridinone and 3-(2-hydroxyphenyl)hydantoin derivatives and evaluated their activity as novel quorum sensing (QS) inhibitors. We found that benzoxazolone and oxazolopyridinone derivatives had promising QS inhibitory activity in the minimum inhibitory concentration, pyocyanin and rhamnolipid inhibition assays. In particular, A10 and B20 at 256 µg/mL not only suppressed pyocyanin production regulated by QS in P. aeruginosa PAO1 by 36.55% and 46.90%, respectively, but also showed the strongest rhamnolipid inhibitory activity with the IC50 values of 66.35 and 56.75 µg/mL, respectively. Further studies demonstrated that B20 at 64 µg/mL inhibited biofilm formation in P. aeruginosa PAO1 by 40%, and weakened its swarming motility. More importantly, the bacterial mortality of B20 combined with ciprofloxacin and clarithromycin against P. aeruginosa were 48.27% and 49.79%, respectively, while ciprofloxacin and clarithromycin had only 16.99% and 29.11% of bacterial mortality against P. aeruginosa when used alone. Mechanistic studies indicated that B20 directly inhibited the QS pathway based on the GFP reporter strain assay. Overall, this compound with oxazolopyridinone core could serve as an antibacterial lead of QS inhibitor for further evaluation of its drug-likeness.

Design, synthesis and antibacterial evaluation of novel C-11, C-9 or C-2'-substituted 3-O-descladinosyl-3-ketoclarithromycin derivatives.

A novel series of 3-O-descladinosyl-3-keto-clarithromycin derivatives, including 11-O-carbamoyl-3-O-descladinosyl-3-keto-clarithromycin derivatives and 2',9(S)-diaryl-3-O-descladinosyl-3-keto-clarithromycin derivatives, were designed, synthesized and evaluated for their in vitro antibacterial activity. Among them, some derivatives were found to have activity against resistant bacteria strains. In particular, compound 9b showed not only the most significantly improved activity (16 µg/mL) against S. aureus ATCC43300 and S. aureus ATCC31007, which was >16-fold more active than that of CAM and AZM, but also the best activity against S. pneumoniae B1 and S. pyogenes R1, with MIC values of 32 and 32 µg/mL. In addition, compounds 9a, 9c, 9d and 9g exhibited the most effective activity against S. pneumoniae AB11 with MIC values of 32 or 64 µg/mL as well. Unfortunately, 2',9(S)-diaryl-3-O-descladinosyl-3-keto-clarithromycin derivatives failed to exhibit better antibacterial activity than references. It can be seen that the combined modification of the C-3 and C-11 positions of clarithromycin is beneficial to improve activity against resistant bacteria, while the single modification of the C-2'' position is very detrimental to antibacterial activity.