During infection, bacteria use an arsenal of resistance mechanisms to negate antibiotic therapies. In addition, pathogenic bacteria form surface-attached biofilms bearing enriched populations of metabolically dormant persister cells. Bacteria develop resistance in response to antibiotic insults; however, nonreplicating biofilms are innately tolerant to all classes of antibiotics. As such, molecules that can eradicate antibiotic-resistant and antibiotic-tolerant bacteria are of importance. Here, we report modular synthetic routes to fluorine-containing halogenated phenazine (HP) and halogenated acridine (HA) agents with potent antibacterial and biofilm-killing activities. Nine fluorinated phenazines were rapidly accessed through a synthetic strategy involving (1) oxidation of fluorinated anilines to azobenzene intermediates, (2) SNAr with 2-methoxyaniline, and (3) cyclization to phenazines upon treatment with trifluoroacetic acid. Five structurally related acridine heterocycles were synthesized using SNAr and Buchwald-Hartwig approaches. From this focused collection, phenazines 5g, 5h, 5i, and acridine 9c demonstrated potent antibacterial activities against Gram-positive pathogens (MIC = 0.04-0.78 μM). Additionally, 5g and 9c eradicated Staphylococcus aureus, Staphylococcus epidermidis and Enterococcus faecalis biofilms with excellent potency (5g, MBEC = 4.69-6.25 μM; 9c, MBEC = 4.69-50 μM). Using real-time quantitative polymerase chain reaction (RT-qPCR), 5g, 5h, 5i, and 9c rapidly induce the transcription of iron uptake biomarkers isdB and sbnC in methicillin-resistant S. aureus (MRSA) biofilms, and we conclude that these agents operate through iron starvation. Overall, fluorinated phenazine and acridine agents could lead to ground-breaking advances in the treatment of challenging bacterial infections.
Keywords: antibacterial agents; biofilm-eradicating agents; chemical synthesis; halogenated acridine; halogenated phenazine; iron starvation.