Small azobenzene derivatives active against bacteria and fungi

A Flash Conversion to Aromatic Azo Compounds Expedited by Hydrazine-Trifluoroacetate Hydrogen Bonding

Aromatic azo compounds are very useful chemicals, but rapid and safe synthetic methods for preparing these compounds are underexplored. An extremely fast reaction was developed to prepare aromatic azo compounds from commercially available quinones and aryl hydrazinium chloride salts. The reactions could be completed within 2 min, in the presence of sodium trifluoroacetate under ambient conditions. A hydrazine-trifluoroacetate hydrogen bonding complex likely inhibited byproducts and greatly accelerated the reaction. The overall procedure is extremely simple and does not require sophisticated synthetic organic equipment and techniques.

Methicillin-Resistant Staphylococcus aureus Inhibitory Activity of some New Thiazole-Based Schiff Bases: One-pot Synthesis and In Vitro Screening

Twelve thiazole-based Schiff bases derived from salicylaldehyde derivatives are efficiently prepared in the current study. A typical Hantzsch thiazole reaction was used to prepare the targeted molecules in 80%-92%. Therefore, a one-pot protocol was developed involving the reaction of salicylaldehydes, thiosemicarbazide, and the appropriate hydrazonyl chlorides in dioxane at reflux for 5-6 h in the presence of one equivalent of triethylamine. The new products were tested against six different American Type Culture Collection bacterial strains with the reference ciprofloxacin. In general, integrating an aryldiazenyl unit into the structure of the tested 4-methylthiazole-based Schiff bases at thiazole-C5 resulted in improved antibacterial activity. Moreover, Schiff bases linked to 5-((4-chlorophenyl)thio)methyl units outperformed their analogs linked to 5-(phenyl)thio)methyl units by 2-fold. Thiazole-based Schiff base linked to 5-((4-chlorophenyl)thio)methyl and 5-((4-methoxyphenyl)diazenyl) units showed the highest activity against all strains tested, particularly Staphylococcus aureus and Enterococcus faecalis. It had minimum inhibitory concentration/minimum bactericidal concentration (MIC/MBC) up to 7.4/14.9 µM. Moreover, it demonstrated comparable Methicillin-resistant S. aureus (MRSA) inhibitory activity to linezolid against two MRSA strains with MIC/MBC up to 7.4/29.8 µM.

MRSA Inhibitory Activity of Some New Pyrazolo[1,5-a]pyrimidines Linked to Arene and/or Furan or Thiophene Units

Methicillin-resistant Staphylococcus aureus (MRSA) is a major contributor to hospital-acquired infections and is highly resistant to treatment. Ongoing research focuses on developing new antimicrobial medications to prevent the spread of resistance. A facile method was employed to efficiently synthesize new pyrazolo[1,5-a]pyrimidines in 84-93 % yields by reacting 4-benzyl-1H-pyrazole-3,5-diamine with the respective α,β-unsaturated ketones. The reaction was carried out in ethanol containing 1.2 equivalents of potassium hydroxide at reflux for 5-6 h. The new products are attached to a para-substituted aryl group with variable electronic properties at pyrazolopyrimidine-C5, in addition to one of three units at C7, namely phenyl, thiophen-2-yl, or furan-2-yl units. A wide spectrum of antibacterial activity was displayed by the new pyrimidines against six different bacterial strains. In general, pyrimidines attached to furan-2-yl units at C7, in addition to another aryl unit at C5, attached to 4-Me or 4-OMe groups, demonstrate significant antibacterial activity, particularly against S. aureus strain. They had MIC/MBC of 2.5/5.1 and 2.4/4.9 μM, respectively, which exceeded that of ciprofloxacin. Moreover, they demonstrate more effective MRSA inhibitory activity than linezolid, with MIC/MBC values up to 4.9/19.7 and 2.4/19.7 μM against MRSA ATCC:33591 and ATCC:43300 strains, respectively.

Crystal structure, Hirshfeld surface, DFT and mol-ecular docking studies of 2-{4-[(E)-(4-acetylphen-yl)diazen-yl]phen-yl}-1-(5-bromo-thio-phen-2-yl)ethanone; a compound with bromine⋯oxygen-type contacts

The title compound, C19H13BrN2O3S, a non-liquid crystal mol-ecule, crystallizes in the ortho-rhom-bic system, space group Pna21. The torsion angles associated with ester and azo groups are -177.0 (4)°, -anti-periplanar, and 179.0 (4)°, +anti-periplanar, respectively. The packing is consolidated by a weak C-Br⋯O=C contact, forming infinite chains running along the [001] direction. A Hirshfeld surface analysis revealed that the major contributions to the crystal surface are from H⋯H, C⋯H/H⋯C, O⋯H/H⋯O, Br⋯H/H⋯Br and S⋯H/H⋯S inter-actions. The computed three-dimensional energy inter-actions using the basis set B3LYP\631-G(d,p) show that Edis (217.6 kJ mol-1) is the major component in the structure. The DFT calculations performed at the B3LYP/6-311+ G(d,p) level indicate that the energy gap between HOMO and LUMO is 3.6725 (2) eV. The mol-ecular electrostatic potential (MEP) map generated supports the existence of the Br⋯O type contact, formed between the electrophilic site of the bromine atom and the nucleophilic site of the ketonic oxygen atom. The mol-ecular docking between the ligand and the Mycobacterium Tuberculosis (PDB ID:1HZP) receptor shows a good binding affinity value of -8.5 kcal mol-1.

Discovery of Novel Nicotinamide Derivatives by a Two-Step Strategy of Azo-Incorporating and Bioisosteric Replacement

Azobenzene moieties can serve as active fragments in antimicrobials and exert trans/cis conversions of molecules. Herein, a series of novel nicotinamide derivatives (NTMs) were developed by employing a two-step strategy, including azo-incorporating and bioisosteric replacement. Azo-incorporation can conveniently provide compounds that can be easily optically interconverted between trans/cis isomers, enhancing the structural diversity of azo compounds. It is noteworthy that the replacement of the azo bond with a 1,2,4-oxadiazole motif through further bioisosteric replacement led to the discovery of a novel compound, NTM18, which made a breakthrough in preventing rice sheath blight disease. A control effect value of 94.44% against Rhizoctonia solani could be observed on NTM18, while only 11.11% was determined for boscalid at 200 mg·L-1. Further mechanism validations were conducted, and the molecular docking analysis demonstrated that compound NTM18 might have a tight binding with SDH via an extra π-π interaction between the oxadiazole ring and residue of D_Y586. This work sets up a typical case for the united applications of azo-incorporating and bioisosteric replacement in fungicide design, posing an innovative approach in structural diversity-based development of pesticides.

Shikonin and Alkannin inhibit ATP synthase and impede the cell growth in Escherichia coli

Naturally occurring naphthoquinones, shikonin and alkannin, are important ingredients of traditional Chinese medicine Zicao. These constituents are reported to have many therapeutic uses, such as wound healing; scar treatment; and anti-inflammation, anti-acne, anti-ulcer, anti-HIV, anticancer, and antibacterial properties. The primary objective of this investigation was to explore the effect of shikonin and alkannin on Escherichia coli ATP synthase and its cell growth. Shikonin caused complete (100 %) inhibition, and alkannin caused partial (79 %) inhibition of wild-type E. coli ATP synthase. Both caused partial (4 %-27 %) inhibition of ATP synthase with genetically modified phytochemical binding site. The growth inhibition of strains expressing normal, deficient, and mutant ATP synthase by shikonin and alkannin, corroborated the inhibition observed in isolated normal wild-type and mutant ATP synthase. Trivial inhibition of mutant enzymes indicated αR283D, αE284R, βV265Q, and γT273A are essential for formation of the phytochemical binding site where shikonin and alkannin bind. Further, shikonin was a potent inhibitor of ATP synthase than alkannin. The antimicrobial properties of shikonin and alkannin were tied to the binding at phytochemical site of microbial ATP synthase. Selective targeting of bacterial ATP synthase by shikonin and alkannin may be an advantageous alternative to address the antibiotic resistance issue.

Antimicrobial potential of quaternary phosphonium salt compounds: a review

Given that mitochondrial dysregulation is a biomarker of many cancers, cationic quaternary phosphonium salt (QPS) conjugation is a widely utilized strategy for anticancer drug design. QPS-conjugated compounds exhibit greater cell permeation and accumulation in negatively charged mitochondria, and thus, show enhanced activity. Phylogenetic similarities between mitochondria and bacteria have provided a rationale for exploring the antibacterial properties of mitochondria-targeted compounds. Additionally, due to the importance of mitochondria in the survival of pathogenic microbes, including fungi and parasites, this strategy can be extended to these organisms as well. This review examines recent literature on the antimicrobial activities of various QPS-conjugated compounds and provides future directions for exploring the medicinal chemistry of these compounds.

Recent Progress in Photoresponsive Biomaterials

Photoresponsive biomaterials have garnered increasing attention recently due to their ability to dynamically regulate biological interactions and cellular behaviors in response to light. This review provides an overview of recent advances in the design, synthesis, and applications of photoresponsive biomaterials, including photochromic molecules, photocleavable linkers, and photoreactive polymers. We highlight the various approaches used to control the photoresponsive behavior of these materials, including modulation of light intensity, wavelength, and duration. Additionally, we discuss the applications of photoresponsive biomaterials in various fields, including drug delivery, tissue engineering, biosensing, and optical storage. A selection of significant cutting-edge articles collected in recent years has been discussed based on the structural pattern and light-responsive performance, focusing mainly on the photoactivity of azobenzene, hydrazone, diarylethenes, and spiropyrans, and the design of smart materials as the most targeted and desirable application. Overall, this review highlights the potential of photoresponsive biomaterials to enable spatiotemporal control of biological processes and opens up exciting opportunities for developing advanced biomaterials with enhanced functionality.

Azobenzene derivatives with activity against drug-resistant Candida albicans and Candida auris

Increasing resistance against antimycotic drugs challenges anti-infective therapies today and contributes to the mortality of infections by drug-resistant Candida species and strains. Therefore, novel antifungal agents are needed. A promising approach in developing new drugs is using naturally occurring molecules as lead structures. In this work, 4,4'-dihydroxyazobenzene, a compound structurally related to antifungal stilbene derivatives and present in Agaricus xanthodermus (yellow stainer), served as a starting point for the synthesis of five azobenzene derivatives. These compounds prevented the growth of both fluconazole-susceptible and fluconazole-resistant Candida albicans and Candida auris strains. Further in vivo studies are required to confirm the potential therapeutic value of these compounds.

Antimicrobial and Antibiofilm Effect of 4,4'-Dihydroxy-azobenzene against Clinically Resistant Staphylococci

The spread of antibiotic resistance among human and animal pathogens is one of the more significant public health concerns. Moreover, the restrictions on the use of particular antibiotics can limit the options for the treatment of infections in veterinary clinical practice. In this context, searching for alternative antimicrobial substances is crucial nowadays. In this study, 4,4'-dihydroxy-azobenzene (DHAB) was tested for its potential in vitro as an antimicrobial agent against two relevant human and animal pathogens, namely Staphylococcus aureus and Staphylococcus pseudintermedius. The values of minimal inhibitory concentration (MIC) were 64 and 32 mg/L respectively, and they comparable to other azo compounds of probed antimicrobial activity. In addition, the minimal bactericidal concentrations (MCB) were 256 and 64 mg/L. The mechanism by which DHAB produces toxicity in staphylococci has been investigated. DHAB caused membrane damage as revealed by the increase in thiobarbituric acid reactive substances (TBARS) such as malondialdehyde. Furthermore, differential induction of the enzymes peroxidases and superoxide dismutase in S. aureus and S. pseudintermedius suggested their prevalent role in ROS-scavenging due to the oxidative burst induced by this compound in either species. In addition, this substance was able to inhibit the formation of biofilms by both bacteria as observed by colorimetric tests and scanning electron microscopy. In order to assess the relevance of DHAB against clinical strains of MRSA, 10 clinical isolates resistant to either methicillin or daptomycin were assayed; 80% of them gave values of CMI and CMB similar to those of the control S. aureus strain. Finally, cutaneous plasters containing a composite formed by an agar base supplemented with DHAB were designed. These plasters were able to inhibit in vitro the growth of S. aureus and S. pseudintermedius, particularly the later, and this suggests that this substance could be a promising candidate as an alternative to antibiotics in the treatment of animal skin infections, as it has been proven that the toxicity of this substance is very low particularly at a dermal level.

Charge-Separated Reactive Intermediates from the UV Photodissociation of Chlorobenzene in Solution

Although ultraviolet (UV)-induced photochemical cleavage of carbon–halogen bonds in gaseous halocarbons is mostly homolytic, the photolysis of chlorobenzene in solution has been proposed to produce a phenyl cation, c-C₆H₅⁺, which is a highly reactive intermediate of potential use in chemical synthesis and N₂ activation. Any evidence for such a route to phenyl cations is indirect, with uncertainty remaining about the possible mechanism. Here, ultrafast transient absorption spectroscopy of UV-excited (λ = 240 and 270 nm) chlorobenzene solutions in fluorinated (perfluorohexane) and protic (ethanol and 2,2,2-trifluoroethanol) solvents reveals a broad electronic absorption band centered at 540 nm that is assigned to an isomer of chlorobenzene with both charge-separated and triplet-spin carbene character. This spectroscopic feature is weaker, or absent, when experiments are conducted in cyclohexane. The intermediate isomer of chlorobenzene has a solvent-dependent lifetime of 30–110 ps, determined by reaction with the solvent or quenching to a lower-lying singlet state. Evidence is presented for dissociation to ortho-benzyne, but the intermediate could also be a precursor to phenyl cation formation.

Insights into Two Novel Orthopalladated Chromophores with Antimicrobial Activity against Escherichia coli

Advanced chromophoric tools, besides being biologically active, need to meet the expectations of the technological demands including stability, colour retention, and proper solubility for their target. Many coordination compounds of conjugated ligands are antibacterial dyes, able to combine a strong dyeing performance with a useful biological activity. Specifically, palladium (II) complexes of Schiff base ligands are known for their relevant activity against common bacteria. In this article, we report the synthesis and comprehensive experimental and theoretical characterization of two novel Pd(II) chromophore complexes obtained from a cyclopalladated Schiff base as two different chelating azo dyes. The antibacterial response of these two novel complexes was tested against the ubiquitous Escherichia coli bacterium in an aqueous medium and revealed a noteworthy antimicrobial activity, higher than when compared with their uncoordinated biologically active ligands.

Azobenzene as Antimicrobial Molecules

Azo molecules, characterized by the presence of a -N=N- double bond, are widely used in various fields due to their sensitivity to external stimuli, ch as light. The emergence of bacterial resistance has pushed research towards designing new antimicrobial molecules that are more efficient than those currently in use. Many authors have attempted to exploit the antimicrobial activity of azobenzene and to utilize their photoisomerization for selective control of the bioactivities of antimicrobial molecules, which is necessary for antibacterial therapy. This review will provide a systematic and consequential approach to coupling azobenzene moiety with active antimicrobial molecules and drugs, including small and large organic molecules, such as peptides. A selection of significant cutting-edge articles collected in recent years has been discussed, based on the structural pattern and antimicrobial performance, focusing especially on the photoactivity of azobenzene and the design of smart materials as the most targeted and desirable application.

Inhibition of Escherichia coli ATP synthase and cell growth by dietary pomegranate phenolics

Historically, people have been using pomegranate to alleviate many disease conditions. Pomegranate is known for its antiinflammatory, antioxidant, neuroprotective, anticancer, and antibacterial properties. In the current study, we examined effects of 8 dietary phenolics present in pomegranate (DPPs)-cyanidin-3-glucoside, cyanin chloride, delphinidin-3-glucoside, delphinidin-3,5-diglucoside, pelargonidin-3-glucoside, pelargonin chloride, punicalagin, and punicalin-on Escherichia coli ATP synthase and cell growth. DPPs caused complete or near complete (89%-100%) inhibition of wild-type E. coli ATP synthase and partial (5%-64%) inhibition of mutant enzymes αR283D, αE284R, βV265Q, and γT273A. Growth inhibition of wild-type, null, and mutant strains in the presence of DPPs were lower than that of isolated wild-type and mutant ATP synthase. On a molar scale, cyanin chloride was the most potent, and pelargonidin-3-glucoside was the least effective inhibitor of wild-type ATP synthase. Partial inhibition of mutant enzymes confirmed that αR283D, αE284R, βV265Q, and γT273A are essential in the formation of the phytochemical binding site. Our results establish that DPPs are potent inhibitors of wild-type E. coli ATP synthase and that the antimicrobial nature of DPPs can be associated with the binding and inhibition of microbial ATP synthase. Additionally, selective inhibition of microbial ATP synthase by DPPs is a useful method to combat antimicrobial resistance.

Inhibition of Escherichia coli ATP synthase by dietary ginger phenolics

For centuries, dietary ginger has been known for its antioxidant, anticancer, and antibacterial properties. In the current study, we examined the link between antibacterial properties of 7 dietary ginger phenolics (DGPs)-gingerenone A, 6-gingerol, 8-gingerol, 10-gingerol, paradol, 6-shogaol, and zingerone-and inhibition of bacterial ATP synthase. DGPs caused complete (100%) inhibition of wild-type Escherichia coli membrane-bound F1Fo ATP synthase, but partial and variable (0%-87%) inhibition of phytochemical binding site mutant enzymes αR283D, αE284R, βV265Q, and γT273A. The mutant enzyme ATPase activity was 16-fold to 100-fold lower than that of the wild-type enzyme. The growth of wild-type, null, and mutant strains in the presence of the 7 DGPs were abrogated to variable degrees on limiting glucose and succinate media. DGPs-caused variable inhibitory profiles of wild-type and mutant ATP synthase confirm that residues of α-, β-, and γ-subunits are involved in the formation of phytochemical binding site. The variable degree of growth in the presence of DGPs also indicates the possibility of molecular targets other than ATP synthase. Our results establish that antibacterial properties of DGPs can be linked to the binding and inhibition of bacterial ATP synthase. Therefore, bacterial ATP synthase is a valuable molecular target for DGPs.

Novel stilbene scaffolds efficiently target Mycobacterium tuberculosis nucleoid-associated protein, HU

Novel scaffolds of stilbene were identified as inhibitors of Mycobacterium tuberculosis by targeting the nucleoid-associated protein, HU, using molecular docking.

Stilbenoids: A Natural Arsenal against Bacterial Pathogens

The escalating emergence of resistant bacterial strains is one of the most important threats to human health. With the increasing incidence of multi-drugs infections, there is an urgent need to restock our antibiotic arsenal. Natural products are an invaluable source of inspiration in drug design and development. One of the most widely distributed groups of natural products in the plant kingdom is represented by stilbenoids. Stilbenoids are synthesised by plants as means of protection against pathogens, whereby the potential antimicrobial activity of this class of natural compounds has attracted great interest in the last years. The purpose of this review is to provide an overview of recent achievements in the study of stilbenoids as antimicrobial agents, with particular emphasis on the sources, chemical structures, and the mechanism of action of the most promising natural compounds. Attention has been paid to the main structure modifications on the stilbenoid core that have expanded the antimicrobial activity with respect to the parent natural compounds, opening the possibility of their further development. The collected results highlight the therapeutic versatility of natural and synthetic resveratrol derivatives and provide a prospective insight into their potential development as antimicrobial agents.

Synthesis, in-vitro and in-silico study of novel thiazoles as potent antibacterial agents and MurB inhibitors

Efficient procedures are herein reported for the synthesis of novel hybrid thiazoles via a one-pot three-component protocol. The protocol involves the reaction of novel aldehyde, thiosemicarbazide and halogen-containing reagents in solvent- and catalyst-free conditions. The structures of the new thiazoles were elucidated by elemental analyses and spectroscopic data. The in-vitro antibacterial screening and MurB enzyme inhibition assays were performed for the novel thiazoles. The thiazol-4(5H)-one derivative 6d, with p-MeO, exhibits the best antibacterial activities with minimum inhibitory concentration values of 3.9, 3.9, 7.8, and 15.6 μg/ml against Staphylococcus aureus, Klebsiella pneumoniae, Streptococcus mutans, and Escherichia coli, respectively, as compared to the reference antibiotic drugs. It also exhibits the highest inhibition of the MurB enzyme with an IC₅₀ of 8.1 μM. The structure-activity relationship was studied to determine the effect of the structures of the newly prepared molecules on the strength of the antibacterial activities. Molecular docking was also performed to predict the binding modes of the new thiazoles in the active sites of the E. coli MurB enzyme.

Trojan Antibiotics: New Weapons for Fighting Against Drug Resistance

Bacterial resistance has caused a global healthcare emergency due to the buildup of antibiotics in the environment. Novel approaches that enable highly efficient bactericide and auto inactivation are highly desired. Past researches mainly focused on the on-off bactericidal ability of antibiotics, which often displays unsatisfactory bactericidal efficiency. Herein, we report a Trojan antibiotic that considers the affinity of antibiotics to bacteria. A disguised host-guest supramolecule based on cucurbituril (CB[7]) and a bola-type azobenzene compound with glycosylamine heads at both ends is synthesized. This supramolecule has a surface fully decorated with sugar-like components, which are highly analogous to wall components of bacteria. This Trojan antibiotic is benign to a wide spectrum of bacteria at a weak basic pH of approximately 9.0 under daylight conditions. However, this antibiotic becomes a potent bactericide toward both Gram-negative and Gram-positive bacteria at pH 4.0 under 365 nm UV irradiation. The dual use of pH and UV light greatly enhances the efficiency of the bactericidal effect so that the 50% minimum inhibitory concentration (MIC₅₀) of the Trojan antibiotic is at least 10 times smaller than that of conventional drugs, and the removal of the UV source and reversal of pH automatically stop the antibacterial behavior, which prevents the buildup of active antimicrobial materials in the environment. We expect that the presented Trojan supramolecular strategy may open up a new paradigm in the fight against bacterial resistance.

Synthesis, Characterization, and Cytotoxic Evaluation of Some Newly Substituted Diazene Candidates

A series of azocompounds containing methyl salicylate 4a–k and 1-naphthyl moiety 6–8 was synthesized and tested as anticancer agents. Nitrosation of methyl 5-amino-2-hydroxybenzoate or 1-aminonaphthalene by using NaNO2 in the presence of HCl afforded diazonium salt derivatives 2 and 5, which were treated with substituted imino or substituted amino derivatives, to give the corresponding substituted amino-pent-2-en-3-yl-diazenylbenzoate 4a–k or 2-substituted-1-(naphthalen-1-yl)diazene derivatives 6a–h, 7a,b, and 8a,b. All the synthesized compounds were elucidated by elemental analysis and spectroscopic evidence.

A Therapeutic Connection between Dietary Phytochemicals and ATP Synthase

For centuries, phytochemicals have been used to prevent and cure multiple health ailments. Phytochemicals have been reported to have antioxidant, antidiabetic, antitussive, antiparasitic, anticancer, and antimicrobial properties. Generally, the therapeutic use of phy-tochemicals is based on tradition or word of mouth with few evidence-based studies. Moreo-ver, molecular level interactions or molecular targets for the majority of phytochemicals are unknown. In recent years, antibiotic resistance by microbes has become a major healthcare concern. As such, the use of phytochemicals with antimicrobial properties has become perti-nent. Natural compounds from plants, vegetables, herbs, and spices with strong antimicrobial properties present an excellent opportunity for preventing and combating antibiotic resistant microbial infections. ATP synthase is the fundamental means of cellular energy. Inhibition of ATP synthase may deprive cells of required energy leading to cell death, and a variety of die-tary phytochemicals are known to inhibit ATP synthase. Structural modifications of phyto-chemicals have been shown to increase the inhibitory potency and extent of inhibition. Site-directed mutagenic analysis has elucidated the binding site(s) for some phytochemicals on ATP synthase. Amino acid variations in and around the phytochemical binding sites can re-sult in selective binding and inhibition of microbial ATP synthase. In this review, the therapeu-tic connection between dietary phytochemicals and ATP synthase is summarized based on the inhibition of ATP synthase by dietary phytochemicals. Research suggests selective target-ing of ATP synthase is a valuable alternative molecular level approach to combat antibiotic resistant microbial infections.

Synthesis and Antimicrobial Studies of New Antibacterial Azo-Compounds Active against Staphylococcus aureus and Listeria monocytogenes

Some novel (phenyl-diazenyl)phenols (4a–m) were designed and synthesized to be evaluated for their antibacterial activity. Starting from an active previously-synthesized azobenzene chosen as lead compound, we introduced some modifications and optimization of the structure, in order to improve solubility and drug conveyance. Structures of all newly-synthesized compounds were confirmed by ¹H nuclear magnetic resonance (NMR), mass spectrometry, and UV-Vis spectroscopy. Antibacterial activity of the new compounds was tested with the dilution method against the bacteria strains Listeria monocytogenes, Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa PAO1. All the compounds were selectively active against Gram-positive bacteria. In particular, compounds 4d, 4h, and 4i showed the highest activity against S. aureus and Listeria monocytogenes, reaching remarkable MIC₁₀₀ values of 4 μg/mL and 8 μg/mL. The relationship between antimicrobial activity and compound structure has suggested that the presence of hydroxyl groups seems to be essential for antimicrobial activity of phenolic compounds.

Understanding the link between antimicrobial properties of dietary olive phenolics and bacterial ATP synthase

The naturally occurring olive phenolics tyrosol, hydroxytyrosol, dihydroxyphenylglycol (DHPG), and oleuropein are known to have antioxidant, antitumor, and antibacterial properties. In the current study, we examined whether the antimicrobial properties of tyrosol, hydroxytyrosol, DHPG, and oleuropein were linked to the inhibition of bacterial ATP synthase. Tyrosol, hydroxytyrosol, DHPG, and oleuropein inhibited Escherichia coli wild-type and mutant membrane-bound F1Fo ATP synthase to variable degrees. The growth properties of wild-type, null, and mutant strains in presence of above olive phenolics were also abrogated to variable degrees on limiting glucose and succinate. Tyrosol and oleuropein synergistically inhibited the wild-type enzyme. Comparative wild-type and mutant F1Fo ATP synthase inhibitory profiles suggested that αArg-283 is an important residue and olive phenolics bind at the polyphenol binding pocket of ATP synthase. Growth patterns of wild-type, null, and mutant strains in the presence of tyrosol, hydroxytyrosol, DHPG, and oleuropein also hint at the possibility of additional molecular targets. Our results demonstrated that ATP synthase can be used as a molecular target and the antimicrobial properties of olive phenolics in general and tyrosol in particular can be linked to the binding and inhibition of bacterial ATP synthase.

Structure Modification of an Active Azo-Compound as a Route to New Antimicrobial Compounds

Some novel (phenyl-diazenyl)phenols 3a–g were designed and synthesized to be evaluated for their antimicrobial activity. A previously synthesized molecule, active against bacteria and fungi, was used as lead for modifications and optimization of the structure, by introduction/removal or displacement of hydroxyl groups on the azobenzene rings. The aim of this work was to evaluate the consequent changes of the antimicrobial activity and to validate the hypothesis that, for these compounds, a plausible mechanism could involve an interaction with protein receptors, rather than an interaction with membrane. All newly synthesized compounds were analyzed by ¹H-NMR, DSC thermal analysis and UV-Vis spectroscopy. The in vitro minimal inhibitory concentrations (MIC) of each compound was determined against Gram-positive and Gram-negative bacteria and Candida albicans. Compounds 3b and 3g showed the highest activity against S. aureus and C. albicans, with remarkable MIC values of 10 µg/mL and 3 µg/mL, respectively. Structure-activity relationship studies were capable to rationalize the effect of different substitutions on the phenyl ring of the azobenzene on antimicrobial activity.

Safranal and its analogs inhibit Escherichia coli ATP synthase and cell growth

Safranal, a dominant component of saffron, is known to have antitumor, cytotoxic, and antibacterial properties. In this study, we examined safranal and its structural analogs-thymol, carvacrol, damascenone, cuminol, 2,6,6-trimethyl-2-cyclohexene-1,4-dione (TMCHD), 4-isopropylbenzyl bromide (IPBB), and 4-tert-butylphenol (TBP) induced inhibition of Escherichia coli membrane bound F1Fo ATP synthase. Safranal and its analogs inhibited wild-type enzyme to variable degrees. While safranal caused 100% inhibition of wild-type F1Fo ATP synthase, only about 50% inhibition occurred for αR283D mutant ATP synthase. Moreover, safranal, thymol, carvacrol, damascenone, cuminol, TMCHD, IPBB, and TBP all fully abrogated the growth of wild-type E. coli cells and had partial or no effect on the growth of null and mutant E. coli strains. Therefore, the antimicrobial properties of safranal, thymol, carvacrol, damascenone, cuminol, TMCHD, IPBB, and TBP can be linked to their binding and inhibition of ATP synthase. Total loss of growth in wild-type and partial or no growth loss in null or mutant E. coli strains demonstrates that ATP synthase is a molecular target for safranal and its structural analogs. Partial inhibition of the αArg-283 mutant enzyme establishes that αArg-283 residue is required in the polyphenol binding pocket of ATP synthase for the binding of safranal. Furthermore, partial growth loss for the null and mutant strains in the presence of inhibitors also suggests the role of other targets and residues in the process of inhibition.

Photomodulation of bacterial growth and biofilm formation using carbohydrate-based surfactants

Naturally occurring and synthetic carbohydrate amphiphiles have emerged as a promising class of antimicrobial and antiadhesive agents that act through a number of dynamic and often poorly understood mechanisms. In this paper, we provide the first report on the application of azobenzene trans-cis photoisomerization for effecting spatial and temporal control over bacterial growth and biofilm formation using carbohydrate-based surfactants. Photocontrollable surface tension studies and small angle neutron scattering (SANS) revealed the diverse geometries and dimensions of self-assemblies (micelles) made possible through variation of the head group and UV-visible light irradiation. Using these light-addressable amphiphiles, we demonstrate optical control over the antibacterial activity and formation of biofilms against multi-drug resistant (MDR) Pseudomonas aeruginosa, methicillin-resistant Staphylococcus aureus (MRSA) and Gram-negative Escherichia coli. To probe the mechanism of bioactivity further, we evaluated the impact of trans-cis photoisomerization in these surfactants on bacterial motility and revealed photomodulated enhancement in swarming motility in P. aeruginosa. These light-responsive amphiphiles should attract significant interest as a new class of antibacterial agents and as investigational tools for probing the complex mechanisms underpinning bacterial adhesion and biofilm formation.

Thymoquinone Inhibits Escherichia coli ATP Synthase and Cell Growth

We examined the thymoquinone induced inhibition of purified F1 or membrane bound F1FO E. coli ATP synthase. Both purified F1 and membrane bound F1FO were completely inhibited by thymoquinone with no residual ATPase activity. The process of inhibition was fully reversible and identical in both membrane bound F1Fo and purified F1 preparations. Moreover, thymoquinone induced inhibition of ATP synthase expressing wild-type E. coli cell growth and non-inhibition of ATPase gene deleted null control cells demonstrates that ATP synthase is a molecular target for thymoquinone. This also links the beneficial dietary based antimicrobial and anticancer effects of thymoquinone to its inhibitory action on ATP synthase.