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

Regioselective Halogenation of Lavanducyanin by a Site-Selective Vanadium-Dependent Chloroperoxidase

Halogenated phenazine meroterpenoids are a structurally unusual family of marine actinobacterial natural products that exhibit antibiotic, antibiofilm, and cytotoxic bioactivities. Despite a lack of established phenazine halogenation biochemistry, genomic analysis of Streptomyces sp. CNZ-289, a prolific lavanducyanin and C2-halogenated derivative producer, suggested the involvement of vanadium-dependent haloperoxidases. We subsequently discovered lavanducyanin halogenase (LvcH), characterized it in vitro as a regioselective vanadium-dependent chloroperoxidase, and applied it in late-stage chemoenzymatic synthesis.

Bactericidal and biofilm eradication efficacy of a fluorinated benzimidazole derivative, TFBZ, against methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is a major inducement of nosocomial infections and its biofilm formation render the high tolerance to conventional antibiotics, which highlights the requirement to develop new antimicrobial agents urgently. In this study, we identified a fluorinated benzimidazole derivative, TFBZ, with potent antibacterial efficacy toward planktonic MRSA (MIC = 4 μg/mL, MBC = 8 μg/mL) and its persistent biofilms (≥99%, MBEC = 8 μg/mL). TFBZ manifested significant irreversible time-dependent killing against MRSA as characterized by diminished cell viability, bacterial morphological change and protein leakage. Furthermore, the results from CBD devices, crystal violet assay in conjunction with live/dead staining and scanning electron microscopy confirmed that TFBZ was capable of eradicating preformed MRSA biofilms with high efficiency. Simultaneously, TFBZ reduced the bacterial invasiveness and exerted negligible hemolysis and cytotoxicity toward mammalian cells, which ensuring the robust therapeutic effect on mouse skin abscess model. The transcriptome profiling and quantitative RT-PCR revealed that a set of encoding genes associated with cell adhesion, biofilm formation, translation process, cell wall biosynthesis was consistently downregulated in MRSA biofilms upon exposure to TFBZ. In conclusion, TFBZ holds promise as a valuable candidate for therapeutic applications against MRSA chronic infections.

Halogenated Antimicrobial Agents to Combat Drug-Resistant Pathogens

Antimicrobial resistance presents us with a potential global crisis as it undermines the abilities of conventional antibiotics to combat pathogenic microbes. The history of antimicrobial agents is replete with examples of scaffolds containing halogens. In this review, we discuss the impacts of halogen atoms in various antibiotic types and antimicrobial scaffolds and their modes of action, structure-activity relationships, and the contributions of halogen atoms in antimicrobial activity and drug resistance. Other halogenated molecules, including carbohydrates, peptides, lipids, and polymeric complexes, are also reviewed, and the effects of halogenated scaffolds on pharmacokinetics, pharmacodynamics, and factors affecting antimicrobial and antivirulence activities are presented. Furthermore, the potential of halogenation to circumvent antimicrobial resistance and rejuvenate impotent antibiotics is addressed. This review provides an overview of the significance of halogenation, the abilities of halogens to interact in biomolecular settings and enhance pharmacological properties, and their potential therapeutic usages in preventing a postantibiotic era. SIGNIFICANCE STATEMENT: Antimicrobial resistance and the increasing impotence of antibiotics are critical threats to global health. The roles and importance of halogen atoms in antimicrobial drug scaffolds have been established, but comparatively little is known of their pharmacological impacts on drug resistance and antivirulence activities. This review is the first to extensively evaluate the roles of halogen atoms in various antibiotic classes and pharmacological scaffolds and to provide an overview of their ability to overcome antimicrobial resistance.

Design, synthesis and evaluation of halogenated phenazine antibacterial prodrugs targeting nitroreductase enzymes for activation

It is of great importance to develop new strategies to combat antibiotic resistance. Our lab has discovered halogenated phenazine (HP) analogues that are highly active against multidrug-resistant bacterial pathogens. Here, we report the design, synthesis, and study of a new series of nitroarene-based HP prodrugs that leverage intracellular nitroreductase (NTR) enzymes for activation and subsequent release of active HP agents. Our goals of developing HP prodrugs are to (1) mitigate off-target metal chelation (potential toxicity), (2) possess motifs to facilitate intracellular, bacterial-specific HP release, (3) improve water solubility, and (4) prevent undesirable metabolism (e.g., glucuronidation of HP's phenol). Following the synthesis of HP-nitroarene prodrugs bearing a sulfonate ester linker, NTR-promoted release experiments demonstrated prodrug HP-1-N released 70.1% of parent HP-1 after 16 hours (with only 6.8% HP-1 release without NTR). In analogous in vitro experiments, no HP release was observed for control sulfonate ester compounds lacking the critical nitro group. When compared to parent HP compounds, nitroarene prodrugs evaluated during these studies demonstrate similar antibacterial activities in MIC and zone of inhibition assays (against lab strains and clinical isolates). In conclusion, HP-nitroarene prodrugs could provide a future avenue to develop potent agents that target antibiotic resistant bacteria.

[1,2,4]triazolo[4,3-a]quinoxaline as Novel Scaffold in the Imiqualines Family: Candidates with Cytotoxic Activities on Melanoma Cell Lines

Cutaneous melanoma is one of the most aggressive human cancers and is the deadliest form of skin cancer, essentially due to metastases. Novel therapies are always required, since cutaneous melanoma develop resistance to oncogenic pathway inhibition treatment. The Imiqualine family is composed of heterocycles diversely substituted around imidazo[1,2-a]quinoxaline, imidazo[1,2-a]pyrazine, imidazo[1,5-a]quinoxaline, and pyrazolo[1,5-a]quinoxaline scaffolds, which display interesting activities on a panel of cancer cell lines, especially melanoma cell lines. We have designed and prepared novel compounds based on the [1,2,4]triazolo[4,3-a]quinoxaline scaffold through a common synthetic route, using 1-chloro-2-hydrazinoquinoxaline and an appropriate aldehyde. Cyclization is ensured by an oxidation-reduction mechanism using chloranil. The substituents on positions 1 and 8 were chosen based on previous structure-activity relationship (SAR) studies conducted within our heterocyclic Imiqualine family. Physicochemical parameters of all compounds have also been predicted. A375 melanoma cell line viability has been evaluated for 16 compounds. Among them, three novel [1,2,4]triazolo[4,3-a]quinoxalines display cytotoxic activities. Compounds 16a and 16b demonstrate relative activities in the micromolar range (respectively, 3158 nM and 3527 nM). Compound 17a shows the best EC₅₀ of the novel series (365 nM), even if EAPB02303 remains the lead of the entire Imiqualine family (3 nM).

Combating Antimicrobial Resistance in the Post-Genomic Era: Rapid Antibiotic Discovery

Constantly evolving drug-resistant "superbugs" have caused an urgent demand for novel antimicrobial agents. Natural products and their analogs have been a prolific source of antimicrobial agents, even though a high rediscovery rate and less targeted research has made the field challenging in the pre-genomic era. With recent advancements in technology, natural product research is gaining new life. Genome mining has allowed for more targeted excavation of biosynthetic potential from natural sources that was previously overlooked. Researchers use bioinformatic algorithms to rapidly identify and predict antimicrobial candidates by studying the genome before even entering the lab. In addition, synthetic biology and advanced analytical instruments enable the accelerated identification of novel antibiotics with distinct structures. Here, we reviewed the literature for noteworthy examples of novel antimicrobial agents discovered through various methodologies, highlighting the candidates with potent effectiveness against antimicrobial-resistant pathogens.

Design, Synthesis, and Evaluation of Carbonate-Linked Halogenated Phenazine-Quinone Prodrugs with Improved Water-Solubility and Potent Antibacterial Profiles

Pathogenic bacteria have devastating impacts on human health as a result of acquired antibiotic resistance and innate tolerance. Every class of our current antibiotic arsenal was initially discovered as growth-inhibiting agents that target actively replicating (individual, free-floating) planktonic bacteria. Bacteria are notorious for utilizing a diversity of resistance mechanisms to overcome the action of conventional antibiotic therapies and forming surface-attached biofilm communities enriched in (non-replicating) persister cells. To address problems associated with pathogenic bacteria, our group is developing halogenated phenazine (HP) molecules that demonstrate potent antibacterial and biofilm-eradicating activities through a unique iron starvation mode of action. In this study, we designed, synthesized, and investigated a focused collection of carbonate-linked HP prodrugs bearing a quinone trigger to target the reductive cytoplasm of bacteria for bioactivation and subsequent HP release. The quinone moiety also contains a polyethylene glycol group, which dramatically enhances the water-solubility properties of the HP-quinone prodrugs reported herein. We found carbonate-linked HP-quinone prodrugs 11, 21-23 to demonstrate good linker stability, rapid release of the active HP warhead following dithiothreitol (reductive) treatment, and potent antibacterial activities against methicillin-resistant Staphylococcus aureus (MRSA), methicillin-resistant Staphylococcus epidermidis, and Enterococcus faecalis. In addition, HP-quinone prodrug 21 induced rapid iron starvation in MRSA and S. epidermidis biofilms, illustrating prodrug action within these surface-attached communities. Overall, we are highly encouraged by these findings and believe that HP prodrugs have the potential to address antibiotic resistant and tolerant bacterial infections.

Synthesis of Nonsymmetrically Substituted 2,3-Dialkoxyphenazine Derivatives and Preliminary Examination of Their Cytotoxicity

Fourteen new 2,3-dialkoxyphenazine derivatives with two different alkoxy groups bearing R¹ and R² alkyl chains, defined as -CH₂CH(CH₃)₂ and -(CH₂)_n-1CH₃ for n = 1, 2, 4, 6, 8, and 10, were prepared via regioselective synthesis. The applied synthetic protocol is based on the following reactions: the Buchwald-Hartwig coupling of a nonsymmetrically substituted 4,5-dialkoxy-2-nitroaniline with a 1-bromo-2-nitrobenzene derivative featuring additional tert-butyl, trifluoromethyl or two methoxy groups; the reduction of bis(2-nitrophenyl)amine; and a final step of tandem-like oxidation that leads to the preparation of a heterocyclic phenazine system. The regioselectivity of these steps and the molecular structure of the compounds under investigation were confirmed by nuclear magnetic resonance and additionally by single-crystal X-ray diffraction performed for some examples of 5 and 6 phenazine series. For 7-(tert-butyl)-3-isobutoxy-2-(octyloxy)phenazine (5f), 3-(hexyloxy)-2-isobutoxy-7-(trifluoromethyl)phenazine (6e), and 2,3-bis(hexyloxy)-7,8-dimethoxyphenazine (7), viability and cytotoxicity assays were performed on the LoVo human colon adenocarcinoma cell line, with 5f confirmed to exhibit cytotoxicity.

Targeted Anti-Biofilm Therapy: Dissecting Targets in the Biofilm Life Cycle

Biofilm is a crucial virulence factor for microorganisms that causes chronic infection. After biofilm formation, the bacteria present improve drug tolerance and multifactorial defense mechanisms, which impose significant challenges for the use of antimicrobials. This indicates the urgent need for new targeted technologies and emerging therapeutic strategies. In this review, we focus on the current biofilm-targeting strategies and those under development, including targeting persistent cells, quorum quenching, and phage therapy. We emphasize biofilm-targeting technologies that are supported by blocking the biofilm life cycle, providing a theoretical basis for design of targeting technology that disrupts the biofilm and promotes practical application of antibacterial materials.

Synthesis of 1-substituted phenazines as novel antichlamydial agents

A novel series of 1-substituted phenazines 4a-4l were designed and synthesized via Palladium-catalyzed reactions from 1-phenazine trifluoromethanesulfonate. These phenazines showed antichlamydial activity with IC₅₀ values from 1 to 10 μM. Among them, compounds 4c and 4i exhibited the best antichlamydial activity with IC₅₀ values from 2.06 to 2.74 μM without apparent cytotoxicity to host cells.

Transcript Profiling of Nitroxoline-Treated Biofilms Shows Rapid Up-regulation of Iron Acquisition Gene Clusters

Bacterial biofilms are surface-attached communities of slow- or non-replicating cells embedded within a protective matrix of biomolecules. Unlike free-floating planktonic bacteria, biofilms are innately tolerant to conventional antibiotics and are prevalent in recurring and chronic infections. Nitroxoline, a broad-spectrum biofilm-eradicating agent, was used to probe biofilm viability. Transcript profiling (RNA-seq) showed that 452 of 2594 genes (17.4%) in methicillin-resistant Staphylococcus aureus (MRSA) biofilms were differentially expressed after a 2 h treatment of nitroxoline. WoPPER analysis and time-course validation (RT-qPCR) revealed that gene clusters involved in iron acquisition (sbn, isd, MW2101, MW0695, fhu, and feo) were rapidly up-regulated following nitroxoline treatment, which is indicative of iron starvation in MRSA biofilms. In addition, genes related to oligopeptide transporters and riboflavin biosynthesis were found to be up-regulated, while genes related to carotenoid biosynthesis and nitrate assimilation were down-regulated. RT-qPCR experiments revealed that iron uptake transcripts were also up-regulated in established Staphylococcus epidermidis and Acinetobacter baumannii biofilms following nitroxoline treatment. Overall, we show RNA-seq to be an ideal platform to define cellular pathways critical for biofilm survival, in addition to demonstrating the need these bacterial communities have for iron.

Recent Strategies to Combat Biofilms Using Antimicrobial Agents and Therapeutic Approaches

Biofilms are intricate bacterial assemblages that attach to diverse surfaces using an extracellular polymeric substance that protects them from the host immune system and conventional antibiotics. Biofilms cause chronic infections that result in millions of deaths around the world every year. Since the antibiotic tolerance mechanism in biofilm is different than that of the planktonic cells due to its multicellular structure, the currently available antibiotics are inadequate to treat biofilm-associated infections which have led to an immense need to find newer treatment options. Over the years, various novel antibiofilm compounds able to fight biofilms have been discovered. In this review, we have focused on the recent and intensively researched therapeutic techniques and antibiofilm agents used for biofilm treatment and grouped them according to their type and mode of action. We also discuss some therapeutic approaches that have the potential for future advancement.

Isothiazolone-Nitroxide Hybrids with Activity against Antibiotic-Resistant Staphylococcus aureus Biofilms

Isothiazolones are widely used as biocides in industrial processing systems and personal care products, but their use to treat infections in humans has been hampered by their inherent cytotoxicity. Herein, we report a strategy to alleviate isothiazolone toxicity and improve antibacterial and antibiofilm potency by functionalization with a nitroxide moiety. Isothiazolone-nitroxide hybrids 6 and 22 were prepared over three steps in moderate yields (58 and 36%, respectively) from (Z)-3-(benzylsulfanyl)-propenoic acid. Hybrid 22 displayed better activity (minimum inhibitory concentration (MIC) = 35 μM) than the widely used methylisothiazolinone (MIT 1, MIC = 280 μM) against methicillin-susceptible Staphylococcus aureus (MSSA). Hybrid 22 was even more active against drug-resistant strains, such as vancomycin-resistant Staphylococcus aureus (VRSA, MIC = 8.75 μM) over MIT 1 (MIC = 280 μM). The enhanced antibacterial activity of hybrid 22 over MIT 1 was retained against established MSSA and VRSA biofilms, with minimum biofilm eradication concentration (MBEC) values of 35 and 70 μM, respectively, for 22 (the MBEC value for MIT 1 against both strains was ≥280 μM). No toxicity was observed in human epithelial T24 cells treated with hybrid 22 in concentrations up to 560 μM using a lactate dehydrogenase assay.

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

Pyrazine and Phenazine Heterocycles: Platforms for Total Synthesis and Drug Discovery

There are numerous pyrazine and phenazine compounds that demonstrate biological activities relevant to the treatment of disease. In this review, we discuss pyrazine and phenazine agents that have shown potential therapeutic value, including several clinically used agents. In addition, we cover some basic science related to pyrazine and phenazine heterocycles, which possess interesting reactivity profiles that have been on display in numerous cases of innovative total synthesis approaches, synthetic methodologies, drug discovery efforts, and medicinal chemistry programs. The majority of this review is focused on presenting instructive total synthesis and medicinal chemistry efforts of select pyrazine and phenazine compounds, and we believe these incredible heterocycles offer promise in medicine.

Biosynthesis, regulation, and engineering of natural products from Lysobacter

Covering: up to August 2021Lysobacter is a genus of Gram-negative bacteria that was classified in 1987. Several Lysobacter species are emerging as new biocontrol agents for crop protection in agriculture. Lysobacter are prolific producers of new bioactive natural products that are largely underexplored. So far, several classes of structurally interesting and biologically active natural products have been isolated from Lysobacter. This article reviews the progress in Lysobacter natural product research over the past ten years, including molecular mechanisms for biosynthesis, regulation and mode of action, genome mining of cryptic biosynthetic gene clusters, and metabolic engineering using synthetic biology tools.

Design, synthesis, and antibacterial activity of N-(trifluoromethyl)phenyl substituted pyrazole derivatives

Design and synthesis of N-(trifluoromethyl)phenyl substituted pyrazole derivatives and their potency as antimicrobial agents are described. Several of these novel compounds are effective growth inhibitors of antibiotic-resistant Gram-positive bacteria and prevent the development of biofilms by methicillin-resistant Staphylococcus aureus (MRSA) and Enterococcus faecalis. These compounds eradicated the preformed biofilms effectively and were found to be more effective than the control antibiotic vancomycin. Potent compounds showed low toxicity to cultured human embryonic kidney cells with a selectivity factor of >20. The most promising compound is very potent against meropenem, oxacillin, and vancomycin-resistant clinical isolates of Enterococcus faecium. Investigations into the mode of action by performing macromolecular synthesis inhibition studies showed a broad range of inhibitory effects, suggesting targets that have a global effect on bacterial cell function.

An ether-linked halogenated phenazine-quinone prodrug model for antibacterial applications

Antibiotic-resistant infections present significant challenges to patients. As a result, there is considerable need for new antibacterial therapies that eradicate pathogenic bacteria through non-conventional mechanisms. Our group has identified a series of halogenated phenazine (HP) agents that induce rapid iron starvation that leads to potent killing of methicillin-resistant Staphylococcus aureus biofilms. Here, we report the design, chemical synthesis and microbiological assessment of a HP-quinone ether prodrug model aimed to (1) eliminate general (off-target) iron chelation, and (2) release an active HP agent through the bioreduction of a quinone trigger. Here, we demonstrate prodrug analogue HP-29-Q to have a stable ether linkage that enables HP release and moderate to good antibacterial activities against lab strains and multi-drug resistant clinical isolates.

Strategies and Approaches for Discovery of Small Molecule Disruptors of Biofilm Physiology

Biofilms, the predominant growth mode of microorganisms, pose a significant risk to human health. The protective biofilm matrix, typically composed of exopolysaccharides, proteins, nucleic acids, and lipids, combined with biofilm-grown bacteria’s heterogenous physiology, leads to enhanced fitness and tolerance to traditional methods for treatment. There is a need to identify biofilm inhibitors using diverse approaches and targeting different stages of biofilm formation. This review discusses discovery strategies that successfully identified a wide range of inhibitors and the processes used to characterize their inhibition mechanism and further improvement. Additionally, we examine the structure–activity relationship (SAR) for some of these inhibitors to optimize inhibitor activity.

A Modular Synthetic Route Involving N-Aryl-2-nitrosoaniline Intermediates Leads to a New Series of 3-Substituted Halogenated Phenazine Antibacterial Agents

Pathogenic bacteria demonstrate incredible abilities to evade conventional antibiotics through the development of resistance and formation of dormant, surface-attached biofilms. Therefore, agents that target and eradicate planktonic and biofilm bacteria are of significant interest. We explored a new series of halogenated phenazines (HP) through the use of N-aryl-2-nitrosoaniline synthetic intermediates that enabled functionalization of the 3-position of this scaffold. Several HPs demonstrated potent antibacterial and biofilm-killing activities (e.g., HP 29, against methicillin-resistant Staphylococcus aureus: MIC = 0.075 μM; MBEC = 2.35 μM), and transcriptional analysis revealed that HPs 3, 28, and 29 induce rapid iron starvation in MRSA biofilms. Several HPs demonstrated excellent activities against Mycobacterium tuberculosis (HP 34, MIC = 0.80 μM against CDC1551). This work established new SAR insights, and HP 29 demonstrated efficacy in dorsal wound infection models in mice. Encouraged by these findings, we believe that HPs could lead to significant advances in the treatment of challenging infections.

New prodrugs and analogs of the phenazine 5,10-dioxide natural products iodinin and myxin promote selective cytotoxicity towards human acute myeloid leukemia cells

Novel chemotherapeutic strategies for acute myeloid leukemia (AML) treatment are called for. We have recently demonstrated that the phenazine 5,10-dioxide natural products iodinin (3) and myxin (4) exhibit potent and hypoxia-selective cell death on MOLM-13 human AML cells, and that the N-oxide functionalities are pivotal for the cytotoxic activity. Very few structure-activity relationship studies dedicated to phenazine 5,10-dioxides exist on mammalian cell lines and the present work describes our efforts regarding in vitro lead optimizations of the natural compounds iodinin (3) and myxin (4). Prodrug strategies reveal carbamate side chains to be the optimal phenol-attached group. Derivatives with no oxygen-based substituent (-OH or -OCH3) in the 6th position of the phenazine skeleton upheld potency if alkyl or carbamate side chains were attached to the phenol in position 1. 7,8-Dihalogenated- and 7,8-dimethylated analogs of 1-hydroxyphenazine 5,10-dioxide (21) displayed increased cytotoxic potency in MOLM-13 cells compared to all the other compounds studied. On the other hand, dihalogenated compounds displayed high toxicity towards the cardiomyoblast H9c2 cell line, while MOLM-13 selectivity of the 7,8-dimethylated analogs were less affected. Further, a parallel artificial membrane permeability assay (PAMPA) demonstrated the majority of the synthesized compounds to penetrate cell membranes efficiently, which corresponded to their cytotoxic potency. This work enhances the understanding of the structural characteristics essential for the activity of phenazine 5,10-dioxides, rendering them promising chemotherapeutic agents.

Methicillin-resistance Staphylococcus aureus (MRSA) Pyruvate kinase (PK) inhibitors and Their Antimicrobial Activities

Resistance to antibiotics has been widely existed in the health care and community setting, thus developing a novel aspect of new antibiotics is urgently necessary. Methicillin-resistance Staphylococcus aureus (MRSA) Pyruvate kinase (PK) is crucial to the survive of bacterial, making it a novel antimicrobial target. In the past decade, most reported PK inhibitors including indole, flavonoid, phenazine derivative from natural product small molecules or their analogues, or virtual screening from small molecule compound library. This review covers the PK inhibitors and their antimicrobial activities reported from the beginning of 2011 through the middle of 2020. The Structure Activity Relationships (SARs) was discussed briefly as well.

Evolution of Resistance to Phenazine Antibiotics in Staphylococcus aureus and Its Role During Coinfection with Pseudomonas aeruginosa

In the niches that Staphylococcus aureus and Pseudomonas aeruginosa coinhabit, the later pathogen produces phenazine antibiotics to inhibit the growth of S. aureus. Recently, a group of halogenated phenazines (HPs) has been shown to have potent antimicrobial activities against Staphylococci; however, no HP-resistant mutant has been reported. Here, we demonstrate that S. aureus develops HP-resistance via single amino acid change (Arg116Cys) in a transcriptional repressor TetR21. RNA-seq analysis showed that the TetR21^R116C variation caused drastic up-regulation of an adjacent gene hprS (halogenated phenazine resistance protein of S. aureus). Deletion of the hprS in the TetR21^R116C background restored bacterial susceptibility to HP, while hprS overexpression in S. aureus conferred HP-resistance. The expression of HprS is under tight transcriptional control of the TetR21 via direct binding to the promoter region of hprS. The R116C mutation in TetR21 significantly reduced its DNA binding affinity. Moreover, natural phenazine antibiotics (phenazine-1-carboxylic acid and pyocyanin) and a HP analog (HP-22) are ligands for the TetR21, regulating its repressor activity. Combining homology analysis and LC-MS/MS assay we demonstrated that HprS is a phenazine efflux pump. To the best of our knowledge, we provide the first report of phenazine efflux pump in S. aureus. Interestingly, the TetR21^R116C variation has been found in some clinical S. aureus isolates, and a laboratory strain of S. aureus with TetR21^R116C variation showed enhanced growth competitiveness toward P. aeruginosa and promoted coinfection with P. aeruginosa in the host environment, demonstrating significance of the mutation in host infections.

Design, synthesis and biological evaluation of a halogenated phenazine-erythromycin conjugate prodrug for antibacterial applications

There is a significant need for new antibacterial agents as pathogenic bacteria continue to threaten human health through the acquisition of resistance and tolerance towards existing antibiotics. Over the last several years, our group has been developing a novel series of halogenated phenazines that demonstrate potent antibacterial and biofilm eradication activities against critical Gram-positive pathogens, including: Staphylococcus aureus, Staphylococcus epidermidis and Enterococcus faecium. Here, we report the design, chemical synthesis and initial biological assessment of a halogenated phenazine-erythromycin conjugate prodrug 5 aimed at enhancing the translational potential for halogenated phenazines as a treatment of bacterial infections.

Synthesis and Assessment of 3-Substituted Phenazines as Novel Antichlamydial Agents

BACKGROUND

In the past century, many phenazines were isolated from the marine microorganism, and some of these phenazines possessed potent antibacterial activities. We found that a few of the synthesized 4-substituted phenazines could block the infectivity of chlamydiae without host cell toxicity.

OBJECTIVE

The aim of this study was to design and synthesize two series of novel 3-substituted phenazines to find novel antichlamydial agents.

METHODS

The 3-substituted phenazines were synthesized via Buchwald-Hartwig cross coupling reaction and Suzuki reaction from 3-bromo-1-methoxyphenazine. The antichlamydial activity of these synthesized compounds was evaluated by determining their effect on the yield of infectious progeny EBs. Cytotoxicity of these compounds on host cells was assessed by the treatment of uninfected HeLa cells using WST-1 method.

RESULTS

Most of the 3-substituted phenazines possessed potent antichlamydial activity with IC50 values from 0.15 to 12.08 μM against Chlamydia trachomatis L2, C. muridarum MoPn and C. pneumoniae AR39. Among them, 7d and 9a exhibited better antichlamydial activity with IC50 values from 0.20 to 1.01 μM while they have no apparent cytotoxicity to host cells. Biological assay disclosed that both 7d and 9a inhibited chlamydial infection by reducing elementary body infectivity and disturbing chlamydial growth during the whole chlamydial developmental cycle.

CONCLUSION

Our findings suggested that 3-substituted phenazine derivatives might be a promising class of therapeutic agents for chlamydial infections. More effective phenazines with low toxicity could be acquired through further chemical modification on C-3 position rather than C-4 position of phenazine.

Therapeutic Strategies To Counteract Antibiotic Resistance in MRSA Biofilm-Associated Infections

Methicillin-resistant Staphylococcus aureus (MRSA) has emerged as one of the leading causes of persistent human infections. This pathogen is widespread and is able to colonize asymptomatically about a third of the population, causing moderate to severe infections. It is currently considered the most common cause of nosocomial infections and one of the main causes of death in hospitalized patients. Due to its high morbidity and mortality rate and its ability to resist most antibiotics on the market, it has been termed a "superbug". Its ability to form biofilms on biotic and abiotic surfaces seems to be the primarily means of MRSA antibiotic resistance and pervasiveness. Importantly, more than 80 % of bacterial infections are biofilm-mediated. Biofilm formation on indwelling catheters, prosthetic devices and implants is recognized as the cause of serious chronic infections in hospital environments. In this review we discuss the most relevant literature of the last five years concerning the development of synthetic small molecules able to inhibit biofilm formation or to eradicate or disperse pre-formed biofilms in the fight against MRSA diseases. The aim is to provide guidelines for the development of new anti-virulence strategies based on the knowledge so far acquired, and, to identify the main flaws of this research field, which have hindered the generation of new market-approved anti-MRSA drugs that are able to act against biofilm-associated infections.

Natural products as inspiration for the development of bacterial antibiofilm agents

Natural products have historically been a rich source of diverse chemical matter with numerous biological activities, and have played an important role in drug discovery in many areas including infectious disease. Synthetic and medicinal chemistry have been, and continue to be, important tools to realize the potential of natural products as therapeutics and as chemical probes. The formation of biofilms by bacteria in an infection setting is a significant factor in the recalcitrance of many bacterial infections, conferring increased tolerance to many antibiotics and to the host immune response, and as yet there are no approved therapeutics for combatting biofilm-based bacterial infections. Small molecules that interfere with the ability of bacteria to form and maintain biofilms can overcome antibiotic tolerance conferred by the biofilm phenotype, and have the potential to form combination therapies with conventional antibiotics. Many natural products with anti-biofilm activity have been identified from plants, microbes, and marine life, including: elligic acid glycosides, hamamelitannin, carolacton, skyllamycins, promysalin, phenazines, bromoageliferin, flustramine C, meridianin D, and brominated furanones. Total synthesis and medicinal chemistry programs have facilitated structure confirmation, identification of critical structural motifs, better understanding of mechanistic pathways, and the development of more potent, more accessible, or more pharmacologically favorable derivatives of anti-biofilm natural products.

Synthesis and Cytotoxic Evaluation of N-Alkyl-2-halophenazin-1-ones

In this study, the synthesis of N-alkyl-2-halophenazin-1-ones has been established. Six N-alkyl-2-halophenazin-1-ones, including WS-9659 B and marinocyanins A and B, were synthesized by the direct oxidative condensation of 4-halo-1,2,3-benzenetriol with the corresponding N-alkylbenzene-1,2-diamines. One of the most significant features of the present method is that it can be successfully applied to the synthesis of N-alkyl-2-chlorophenazin-1-ones. The traditional chlorination of N-alkyl-phenazin-1-ones with N-chlorosuccinimide selectively occurs at the 4-position to afford the undesired N-alkyl-4-chlorophenazin-1-ones. Our synthetic route successfully circumvents this problem, culminating in the first chemical synthesis of WS-9659 B. The cytotoxicity of six N-alkyl-2-halophenazin-1-ones and three N-alkylphenazin-1-ones against human promyelocytic leukemia HL-60, human lung cancer A549, and normal MRC-5 cells was evaluated. Among the compounds tested in this study, 2-chloropyocyanin possesses significant selectivity toward A549 cells. The cytotoxic evaluation provides structural insights into the potency and selectivity of these compounds for cancer cells.

Progress towards a stable cephalosporin-halogenated phenazine conjugate for antibacterial prodrug applications

Resistant bacteria successfully evade the action of conventional antibiotic therapies during infection, often leading to significant illness and death. Our lab has discovered halogenated phenazine (HP) analogues which demonstrate potent antibacterial activities through a unique iron-starving mechanism. Herein, we describe synthetic efforts towards a stable cephalosporin-HP conjugate prodrug with the aim of translating HPs into useful clinical agents. Cephalosporin-antibiotic conjugates offer multiple advantages for antibacterial design, including the release of active agents through the targeting of intracellular cephalosporinase following selective ring-opening of the beta-lactam warhead. During these studies, carbonate-linked cephalosporin-HP conjugate 16 was synthesized; however, we were unable to successfully remove the ester group required for cephalosporinase processing. Cephalosporin-HP 16 was then utilized as a probe to investigate the stability of the carbonate linker in antibacterial assays and, as predicted, this compound proved to be inactive against Staphylococcus aureus (MIC > 100 µM). The lack of 16's antibacterial activity can be attributed to the carbonate linker remaining intact throughout the MIC assay, thus not liberating the active HP moiety. These efforts have led to a more stable cephalosporin-HP conjugate joined through a carbonate linker compared to a highly unstable ether linked analogue we previously reported.

Instructive Advances in Chemical Microbiology Inspired by Nature's Diverse Inventory of Molecules

Natural product antibiotics have played an essential role in the treatment of bacterial infection in addition to serving as useful tools to explore the intricate biology of bacteria. Our current arsenal of antibiotics operate through the inhibition of well-defined bacterial targets critical for replication and growth. Pathogenic bacteria effectively utilize a diversity of mechanisms that lead to acquired resistance and/or innate tolerance toward antibiotic therapies, which can result in devastating consequences to human life. Several research groups have established innovative programs that work at the chemistry-biology interface to develop new molecules that aim to define and address concerns related to antibiotic resistance and tolerance. In this Review, we present recent progress by select research groups that highlight a diversity of integrated chemical biology and medicinal chemistry approaches aimed at the development and utilization of chemical tools that have led to promising new microbiological insights that may lead to significant clinical advances regarding the treatment of pathogenic bacteria.

Efficacy data of halogenated phenazine and quinoline agents and an NH125 analogue to veterinary mycoplasmas

BACKGROUND

Mycoplasmas primarily cause respiratory or urogenital tract infections impacting avian, bovine, canine, caprine, murine, and reptilian hosts. In animal husbandry, mycoplasmas cause reduced feed-conversion, decreased egg production, arthritis, hypogalactia or agalactia, increased condemnations, culling, and mortality in some cases. Antibiotics reduce transmission and mitigate clinical signs; however, concerning levels of antibiotic resistance in Mycoplasma gallisepticum and M. capricolum isolates exist. To address these issues, we evaluated the minimum inhibitory concentrations (MICs) of halogenated phenazine and quinoline compounds, an N-arylated NH125 analogue, and triclosan against six representative veterinary mycoplasmas via microbroth or agar dilution methods. Thereafter, we evaluated the minimum bactericidal concentration (MBC) of efficacious drugs.

RESULTS

We identified several compounds with MICs ≤25 μM against M. pulmonis (n = 5), M. capricolum (n = 4), M. gallisepticum (n = 3), M. alligatoris (n = 3), M. agassizii (n = 2), and M. canis (n = 1). An N-arylated NH125 analogue, compound 21, served as the most efficacious, having a MIC ≤25 μM against all mycoplasmas tested, followed by two quinolines, nitroxoline (compound 12) and compound 20, which were effective against four and three mycoplasma type strains, respectively. Nitroxoline exhibited bactericidal activity among all susceptible mycoplasmas, and compound 21 exhibited bactericidal activity when the MBC was able to be determined.

CONCLUSIONS

These findings highlight a number of promising agents from novel drug classes with potential applications to treat veterinary mycoplasma infections and present the opportunity to evaluate preliminary pharmacokinetic indices using M. pulmonis in rodents as an animal model of human infection.

Nitroxide Functionalized Antibiotics Are Promising Eradication Agents against Staphylococcus aureus Biofilms

Treatment of biofilm-related Staphylococcus aureus infections represents an important medical challenge worldwide, as biofilms, even those involving drug-susceptible S. aureus strains, are highly refractory to conventional antibiotic therapy. Nitroxides were recently shown to induce the dispersal of Gram-negative biofilms in vitro, but their action against Gram-positive bacterial biofilms remains unknown. Here, we demonstrate that the biofilm dispersal activity of nitroxides extends to S. aureus, a clinically important Gram-positive pathogen. Coadministration of the nitroxide CTEMPO (4-carboxy-2,2,6,6-tetramethylpiperidin-1-yloxyl) with ciprofloxacin significantly improved the biofilm eradication activity of the antibiotic against S. aureus Moreover, covalently linking the nitroxide to the antibiotic moiety further reduced the ciprofloxacin minimal biofilm eradication concentration. Microscopy analysis revealed that fluorescent nitroxide-antibiotic hybrids could penetrate S. aureus biofilms and enter cells localized at the surface and base of the biofilm structure. No toxicity to human cells was observed for the nitroxide CTEMPO or the nitroxide-antibiotic hybrids. Taken together, our results show that nitroxides can mediate the dispersal of Gram-positive biofilms and that dual-acting biofilm eradication antibiotics may provide broad-spectrum therapies for the treatment of biofilm-related infections.

Phenazine Antibiotic-Inspired Discovery of Bacterial Biofilm-Eradicating Agents

Bacterial biofilms are surface-attached communities of slow-growing and non-replicating persister cells that demonstrate high levels of antibiotic tolerance. Biofilms occur in nearly 80 % of infections and present unique challenges to our current arsenal of antibiotic therapies, all of which were initially discovered for their abilities to target rapidly dividing, free-floating planktonic bacteria. Bacterial biofilms are credited as the underlying cause of chronic and recurring bacterial infections. Innovative approaches are required to identify new small molecules that operate through bacterial growth-independent mechanisms to effectively eradicate biofilms. One source of inspiration comes from within the lungs of young cystic fibrosis (CF) patients, who often endure persistent Staphylococcus aureus infections. As these CF patients age, Pseudomonas aeruginosa co-infects the lungs and utilizes phenazine antibiotics to eradicate the established S. aureus infection. Our group has taken a special interest in this microbial competition strategy and we are investigating the potential of phenazine antibiotic-inspired compounds and synthetic analogues thereof to eradicate persistent bacterial biofilms. To discover new biofilm-eradicating agents, we have established an interdisciplinary research program involving synthetic medicinal chemistry, microbiology and molecular biology. From these efforts, we have identified a series of halogenated phenazines (HPs) that potently eradicate bacterial biofilms, and future work aims to translate these preliminary findings into ground-breaking clinical advances for the treatment of persistent biofilm infections.

Recent Progress in Natural-Product-Inspired Programs Aimed To Address Antibiotic Resistance and Tolerance

Bacteria utilize multiple mechanisms that enable them to gain or acquire resistance to antibiotic therapies during the treatment of infections. In addition, bacteria form biofilms which are surface-attached communities of enriched populations containing persister cells encased within a protective extracellular matrix of biomolecules, leading to chronic and recurring antibiotic-tolerant infections. Antibiotic resistance and tolerance are major global problems that require innovative therapeutic strategies to address the challenges associated with pathogenic bacteria. Historically, natural products have played a critical role in bringing new therapies to the clinic to treat life-threatening bacterial infections. This Perspective provides an overview of antibiotic resistance and tolerance and highlights recent advances (chemistry, biology, drug discovery, and development) from various research programs involved in the discovery of new antibacterial agents inspired by a diverse series of natural product antibiotics.

Turning the Tide against Antibiotic Resistance by Evaluating Novel, Halogenated Phenazine, Quinoline, and NH125 Compounds against Ureaplasma Species Clinical Isolates and Mycoplasma Type Strains

Escalating levels of antibiotic resistance in mycoplasmas, particularly macrolide resistance in Mycoplasma pneumoniae and M. genitalium, have narrowed our antibiotic arsenal. Further, mycoplasmas lack a cell wall and do not synthesize folic acid, rendering common antibiotics, such as beta-lactams, vancomycin, sulfonamides, and trimethoprim, of no value.

Escalating levels of antibiotic resistance in mycoplasmas, particularly macrolide resistance in Mycoplasma pneumoniae and M. genitalium, have narrowed our antibiotic arsenal. Further, mycoplasmas lack a cell wall and do not synthesize folic acid, rendering common antibiotics, such as beta-lactams, vancomycin, sulfonamides, and trimethoprim, of no value. To address this shortage, we screened nitroxoline, triclosan, and a library of 20 novel, halogenated phenazine, quinoline, and NH125 analogues against Ureaplasma species and M. hominis clinical isolates from urine. We tested a subset of these compounds (n = 9) against four mycoplasma type strains (M. pneumoniae, M. genitalium, M. hominis, and Ureaplasma urealyticum) using a validated broth microdilution or agar dilution method. Among 72 Ureaplasma species clinical isolates, nitroxoline proved most effective (MIC₉₀, 6.25 µM), followed by an N-arylated NH125 analogue (MIC₉₀, 12.5 µM). NH125 and its analogue had significantly higher MICs against U. urealyticum isolates than against U. parvum isolates, whereas nitroxoline did not. Nitroxoline exhibited bactericidal activity against U. parvum isolates but bacteriostatic activity against the majority of U. urealyticum isolates. Among the type strains, the compounds had the greatest activity against M. pneumoniae and M. genitalium, with 8 (80%) and 5 (71.4%) isolates demonstrating MICs of ≤12.5 µM, respectively. Triclosan also exhibited lower MICs against M. pneumoniae and M. genitalium. Overall, we identified a promising range of quinoline, halogenated phenazine, and NH125 compounds that showed effectiveness against M. pneumoniae and M. genitalium and found that nitroxoline, approved for use outside the United States for the treatment of urinary tract infections, and an N-arylated NH125 analogue demonstrated low MICs against Ureaplasma species isolates.

Eradicating uropathogenic Escherichia coli biofilms with a ciprofloxacin-dinitroxide conjugate

Urinary tract infections (UTIs) are amongst the most common and prevalent infectious diseases worldwide, with uropathogenic Escherichia coli (UPEC) reported as the main causative pathogen. Fluoroquinolone antibiotics are commonly used to treat UTIs but for infections involving UPEC biofilms, which are commonly associated with catheter use and recurrent episodes, ciprofloxacin is often ineffective. Here we report the development of a ciprofloxacin-dinitroxide (CDN) conjugate with potent UPEC biofilm-eradication activity. CDN 11 exhibited a 2-fold increase in potency over the parent antibiotic ciprofloxacin against UPEC biofilms. Moreover, CDN 11 resulted in almost complete UPEC biofilm cell eradication (99.7%) at concentrations as low as 12.5 μM, and significantly potentiated ciprofloxacin's biofilm-eradication activity against UPEC upon co-administration. The biofilm-eradication activity of CDN 11 highlights the potential of nitroxide functionalized antibiotics as a promising strategy for the treatment of biofilm-related UTIs.

Synthesis and Antichlamydial Activity of Novel Phenazines

Results:

C-4 morpholinyl 8a and C-4 phenyl phenazine 9c exhibited stronger antichlamydial activity with no apparent cytotoxicity. Both phenazine derivatives inhibited chlamydial inclusions formation and growth in a dose-dependent manner. They inhibited Chlamydia infection by reducing elementary body infectivity and disturbing Chlamydia growth at the mid-stage of the chlamydial developmental cycle.

Conclusion:

Our findings suggest C-4 aryl and C-4 amino phenazine derivatives as promising lead molecules for antichlamydials development.

The Path to New Halogenated Quinolines With Enhanced Activities Against Staphylococcus epidermidis

Antibiotic-resistant bacteria and surface-attached bacterial biofilms play a significant role in human disease. Conventional antibiotics target actively replicating free-floating, planktonic cells. Unfortunately, biofilm communities are endowed with nonreplicating persister cells that are tolerant to antibiotics. Innovative approaches are necessary to identify new molecules able to eradicate resistant and tolerant bacterial cells. Our group has discovered that select halogenated quinolines (HQs) can eradicate drug-resistant, gram-positive bacterial pathogens and their corresponding biofilms. Interestingly, the HQ scaffold is synthetically tunable and we have discovered unique antibacterial profiles through extensive analogue synthesis and microbiologic studies. We recently reported the synthesis of 14 new HQs to investigate the impact of ClogP values on antibacterial and biofilm eradication activities. We conducted diverse synthetic modifications at the 2-position of the HQ scaffold in an attempt to enhance water solubility and found new compounds that display enhanced activities against Staphylococcus epidermidis. In particular, HQ 2 (ClogP = 3.44) demonstrated more potent antibacterial activities against methicillin-resistant S epidermidis (MRSE) 35984 planktonic cells (minimum inhibitory concentration = 0.59 µM) compared with methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus isolates while demonstrating potent MRSE biofilm eradication activities (minimum biofilm eradication concentration = 2.35 µM). We believe that HQ could play a critical role in the development of next-generation antibacterial therapeutics.

Transcript Profiling of MRSA Biofilms Treated with a Halogenated Phenazine Eradicating Agent: A Platform for Defining Cellular Targets and Pathways Critical to Biofilm Survival

Bacterial biofilms are surface-attached communities of non-replicating bacteria innately tolerant to antibiotics. Biofilms display differential gene expression profiles and physiologies as compared to their planktonic counterparts; however, their biology remains largely unknown. In this study, we used a halogenated phenazine (HP) biofilm eradicator in transcript profiling experiments (RNA-seq) to define cellular targets and pathways critical to biofilm viability. WoPPER analysis with time-course validation (RT-qPCR) revealed that HP-14 induces rapid iron starvation in MRSA biofilms, as evident by the activation of iron-acquisition gene clusters in 1 hour. Serine proteases and oligopeptide transporters were also found to be up-regulated, whereas glycolysis, arginine deiminase, and urease gene clusters were down-regulated. KEGG analysis revealed that HP-14 impacts metabolic and ABC transporter functional pathways. These findings suggest that MRSA biofilm viability relies on iron homeostasis.

Synthetic small molecules as anti-biofilm agents in the struggle against antibiotic resistance

Biofilm formation significantly contributes to microbial survival in hostile environments and it is currently considered a key virulence factor for pathogens responsible for serious chronic infections. In the last decade many efforts have been made to identify new agents able to modulate bacterial biofilm life cycle, and many compounds have shown interesting activities in inhibiting biofilm formation or in dispersing pre-formed biofilms. However, only a few of these compounds were tested using in vivo models for their clinical significance. Contrary to conventional antibiotics, most of the anti-biofilm compounds act as anti-virulence agents as they do not affect bacterial growth. In this review we selected the most relevant literature of the last decade, focusing on the development of synthetic small molecules able to prevent bacterial biofilm formation or to eradicate pre-existing biofilms of clinically relevant Gram-positive and Gram-negative pathogens. In addition, we provide a comprehensive list of the possible targets to counteract biofilm formation and development, as well as a detailed discussion the advantages and disadvantages of the different current biofilm-targeting strategies.

Halogenated quinolines bearing polar functionality at the 2-position: Identification of new antibacterial agents with enhanced activity against Staphylococcus epidermidis

Antibiotic-resistant bacteria and surface-attached biofilms continue to play a significant role in human health and disease. Innovative strategies are needed to identify new therapeutic leads to tackle infections of drug-resistant and tolerant bacteria. We synthesized a focused library of 14 new halogenated quinolines to investigate the impact of ClogP values on antibacterial and biofilm-eradication activities. During these investigations, we found select polar appendages at the 2-position of the HQ scaffold were more well-tolerated than others. We were delighted to see multiple compounds display enhanced activities against the major human pathogen S. epidermidis. In particular, HQ 2 (ClogP = 3.44) demonstrated enhanced activities against MRSE 35984 planktonic cells (MIC = 0.59 μM) compared to MRSA and VRE strains in addition to potent MRSE biofilm eradication activities (MBEC = 2.35 μM). Several of the halogenated quinolines identified here reported low cytotoxicity against HeLa cells with minimal hemolytic activity against red blood cells. We believe that halogenated quinoline small molecules could play an important role in the development of next-generation antibacterial therapeutics capable of targeting and eradicating biofilm-associated infections.

An Efficient Buchwald-Hartwig/Reductive Cyclization for the Scaffold Diversification of Halogenated Phenazines: Potent Antibacterial Targeting, Biofilm Eradication, and Prodrug Exploration

Bacterial biofilms are surface-attached communities comprised of nonreplicating persister cells housed within a protective extracellular matrix. Biofilms display tolerance toward conventional antibiotics, occur in ∼80% of infections, and lead to >500000 deaths annually. We recently identified halogenated phenazine (HP) analogues which demonstrate biofilm-eradicating activities against priority pathogens; however, the synthesis of phenazines presents limitations. Herein, we report a refined HP synthesis which expedited the identification of improved biofilm-eradicating agents. 1-Methoxyphenazine scaffolds were generated through a Buchwald-Hartwig cross-coupling (70% average yield) and subsequent reductive cyclization (68% average yield), expediting the discovery of potent biofilm-eradicating HPs (e.g., 61: MRSA BAA-1707 MBEC = 4.69 μM). We also developed bacterial-selective prodrugs (reductively activated quinone-alkyloxycarbonyloxymethyl moiety) to afford HP 87, which demonstrated excellent antibacterial and biofilm eradication activities against MRSA BAA-1707 (MIC = 0.15 μM, MBEC = 12.5 μM). Furthermore, active HPs herein exhibit negligible cytotoxic or hemolytic effects, highlighting their potential to target biofilms.