Identification of 6,8-ditrifluoromethyl halogenated phenazine as a potent bacterial biofilm-eradicating agent

Bacterial biofilms are surface-attached communities consisting of non-replicating persister cells encased within an extracellular matrix of biomolecules. Unlike bacteria that have acquired resistance to antibiotics, persister cells enable biofilms to demonstrate innate tolerance toward all classes of conventional antibiotic therapies. It is estimated that 50-80% of bacterial infections are biofilm associated, which is considered the underlying cause of chronic and recurring infections. Herein, we report a modular three-step synthetic route to new halogenated phenazine (HP) analogues from diverse aniline and nitroarene building blocks. The HPs were evaluated for antibacterial and biofilm-killing properties against a panel of lab strains and multidrug-resistant clinical isolates. Several HPs demonstrated potent antibacterial (MIC ≤ 0.39 μM) and biofilm-eradicating activities (MBEC < 10 μM) with 6,8-ditrifluoromethyl-HP 15 demonstrated remarkable biofilm-killing potencies (MBEC = 0.15-1.17 μM) against Gram-positive pathogens, including methicillin-resistant Staphylococcus aureus clinical isolates. Confocal microscopy showed HP 15 induced significant losses in the polysaccharide matrix in MRSA biofilms. In addition, HP 15 showed increased antibacterial activities against dormant Mycobacterium tuberculosis (Mtb, MIC = 1.35 μM) when compared to replicating Mtb (MIC = 3.69 μM). Overall, this new modular route has enabled rapid access to an interesting series of potent halogenated phenazine analogues to explore their unique antibacterial and biofilm-killing properties.