Phenazine antibiotic inspired discovery of potent bromophenazine antibacterial agents against Staphylococcus aureus and Staphylococcus epidermidis

Abstract

Nearly all clinically used antibiotics have been (1) discovered from microorganisms (2) using phenotype screens to identify inhibitors of bacterial growth. The effectiveness of these antibiotics is attributed to their endogenous roles as bacterial warfare agents against competing microorganisms. Unfortunately, every class of clinically used antibiotic has been met with drug resistant bacteria. In fact, the emergence of resistant bacterial infections coupled to the dismal pipeline of new antibacterial agents has resulted in a global health care crisis. There is an urgent need for innovative antibacterial strategies and treatment options to effectively combat drug resistant bacterial pathogens. Here, we describe the implementation of a Pseudomonas competition strategy, using redox-active phenazines, to identify novel antibacterial leads against Staphylococcus aureus and Staphylococcus epidermidis. In this report, we describe the chemical synthesis and evaluation of a diverse 27-membered phenazine library. Using this microbial warfare inspired approach, we have identified several bromophenazines with potent antibacterial activities against S. aureus and S. epidermidis. The most potent bromophenazine analogue from this focused library demonstrated a minimum inhibitory concentration (MIC) of 0.78-1.56 μM, or 0.31-0.62 μg mL(-1), against S. aureus and S. epidermidis and proved to be 32- to 64-fold more potent than the phenazine antibiotic pyocyanin in head-to-head MIC experiments. In addition to the discovery of potent antibacterial agents against S. aureus and S. epidermidis, we also report a detailed structure-activity relationship for this class of bromophenazine small molecules.

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

“…In previous studies, we found that some ester groups are well-tolerated while ether- or amine-group substitution of the phenolic hydroxyl group leads to a complete loss of antibacterial activities 22 . The structural requirement for a 1-hydroxyl group (or masked ester/carbonate) on the HP scaffold, coupled with the results from UV-Vis experiments and metal(II) co-treatment MIC profiles, leads us to conclude that non-metal(II) binding carbonates 24 and 25 are prodrugs that release metal(II)-chelators HP 1 and 17 , which bind metal(II)-cations and eradicate planktonic and biofilm cells against susceptible, Gram-positive human pathogens.…”

“…Based on our previous studies, we have found that the HP scaffold 1 requires the 1-hydroxyl group and 2-bromine atom to demonstrate antibacterial activities 22, 25 . In addition, the 4-position is highly active when containing a bromine atom (i.e., HP 1 ), but can also tolerate a butyl group (i.e., HP 2 ) 25 which motivated these investigations as Wohl-Aue reactions could provide synthetic avenues to both 4-brominated and 4-methylated HPs.…”

“…We reasoned that phenazine antibiotic metabolites 20, 21 may be an ideal starting point to explore unique antibacterial agents that eradicate bacterial biofilms. During our initial studies, we explored a diverse panel of phenazine small molecules, including several phenazine antibiotics 22 . From these investigations, we identified the marine phenazine antibiotic 2-bromo-1-hydroxyphenazine and its brominated analogue, 2,4-dibromo-1-hydroxyphenazine 1 , as potent antibacterial agents against S .…”

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 …”

Bioreductively Activated Reactive Oxygen Species (ROS) Generators as MRSA Inhibitors

“…3,4 The ability of such small molecules to keep competitors in check through the generation of reactive oxygen species (ROS) has attracted attention for new drug development. 3,5 ROS including superoxide radical O 2 −• , hydrogen peroxide H 2 O 2 , and hydroxyl radical • OH are generated as a natural consequence of respiration but can cause cellular damage at elevated levels (Scheme 1). 6 Potentiating these ROS in cancers using small molecules has been considered as a possible drug design strategy.…”