Modular Synthetic Routes to Fluorine-Containing Halogenated Phenazine and Acridine Agents That Induce Rapid Iron Starvation in Methicillin-Resistant Staphylococcus aureus Biofilms.

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) S N Ar with 2-methoxyaniline, and (3) cyclization to phenazines upon treatment with trifluoroacetic acid. Five structurally related acridine heterocycles were synthesized using S N Ar 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.