Structure–Activity Relationships of a Diverse Class of Halogenated Phenazines That Targets Persistent, Antibiotic-Tolerant Bacterial Biofilms and Mycobacterium tuberculosis

Abstract

Persistent bacteria, including persister cells within surface-attached biofilms and slow-growing pathogens lead to chronic infections that are tolerant to antibiotics. Here, we describe the structure-activity relationships of a series of halogenated phenazines (HP) inspired by 2-bromo-1-hydroxyphenazine 1. Using multiple synthetic pathways, we probed diverse substitutions of the HP scaffold in the 2-, 4-, 7-, and 8-positions, providing critical information regarding their antibacterial and bacterial eradication profiles. Halogenated phenazine 14 proved to be the most potent biofilm-eradicating agent (≥99.9% persister cell killing) against MRSA (MBEC < 10 μM), MRSE (MBEC = 2.35 μM), and VRE (MBEC = 0.20 μM) biofilms while 11 and 12 demonstrated excellent antibacterial activity against M. tuberculosis (MIC = 3.13 μM). Unlike antimicrobial peptide mimics that eradicate biofilms through the general lysing of membranes, HPs do not lyse red blood cells. HPs are promising agents that effectively target persistent bacteria while demonstrating negligible toxicity against mammalian cells.

A Highly Potent Class of Halogenated Phenazine Antibacterial and Biofilm-Eradicating Agents Accessed Through a Modular Wohl-Aue Synthesis

“…With active HPs targeting both rapidly-dividing planktonic and persistent biofilm cells of Gram-positive pathogens, we felt that HPs could demonstrate antibacterial activities against the persistent pathogen, MtB. We previously reported HPs with good anti-TB activity 24, 25 and, during the course of these studies, we evaluated Wohl-Aue derived HPs for antibacterial activity against MtB H37Ra. We tested a smaller panel of HPs ( 9 , 17 , 18 , 21–23 ; Table 1) that demonstrated potent antibacterial activities against MRSA, MRSE, and VRE.…”

“…epidermidis and Enterococcus faecium 23–25 . Based on our preliminary findings, HPs bind copper(II) and iron(II) and elicit their potent antibacterial activities through a metal(II)-dependent mechanism 25 . Our pursuits have been met with challenges regarding the chemical synthesis of the HP scaffold.…”

“…Our pursuits have been met with challenges regarding the chemical synthesis of the HP scaffold. Our previous work has enabled the exploration of 7,8-disubstituted HPs along with 2,4-mixed halogenations HPs with the use of o -phenylenediamines building blocks 24, 25 ; however, the availability of these building blocks does not enable the level of diversity necessary for our campaign. Our goal for this work is to develop a rapid and convergent synthesis of HP small molecules that enable us to further explore the 6-, 7-, 8- and 9-positions of the HP scaffold through the use of diverse aniline building blocks.…”

Natural Products as Platforms To Overcome Antibiotic Resistance

“…244 This lead inspired further DTS work resulting in a variety of halogenated phenazine analogs (Figure 32), many of which exhibited low micromolar activities against various resistant Gram-positive bacteria. 245 …”

Physiological Evidence for Isopotential Tunneling in the Electron Transport Chain of Methane-Producing Archaea

“…A wide variety of membrane electron carriers are synthesized in nature (26)(27)(28)(29). To determine if similar but nonidentical MPh derivatives are synthesized by methanogens, we extracted lipophilic compounds from membranes of genetically tractable M. acetivorans and M. barkeri (Table 1).…”