Design, Synthesis and Biological Evaluation of Biphenylglyoxamide-Based Small Molecular Antimicrobial Peptide Mimics as Antibacterial Agents.
ABSTRACT: There has been an increasing interest in the development of antimicrobial peptides (AMPs) and their synthetic mimics as a novel class of antibiotics to overcome the rapid emergence of antibiotic resistance. Recently, phenylglyoxamide-based small molecular AMP mimics have been identified as potential leads to treat bacterial infections. In this study, a new series of biphenylglyoxamide-based small molecular AMP mimics were synthesised from the ring-opening reaction of N-sulfonylisatin bearing a biphenyl backbone with a diamine, followed by the conversion into tertiary ammonium chloride, quaternary ammonium iodide and guanidinium hydrochloride salts. Structure-activity relationship studies of the analogues identified the octanesulfonyl group as being essential for both Gram-positive and Gram-negative antibacterial activity, while the biphenyl backbone was important for Gram-negative antibacterial activity. The most potent analogue was identified to be chloro-substituted quaternary ammonium iodide salt 15c, which possesses antibacterial activity against both Gram-positive (MIC against Staphylococcus aureus = 8 ?M) and Gram-negative bacteria (MIC against Escherichia coli = 16 ?M, Pseudomonas aeruginosa = 63 ?M) and disrupted 35% of pre-established S. aureus biofilms at 32 ?M. Cytoplasmic membrane permeability and tethered bilayer lipid membranes (tBLMs) studies suggested that 15c acts as a bacterial membrane disruptor. In addition, in vitro toxicity studies showed that the potent compounds are non-toxic against human cells at therapeutic dosages.
Project description:Contact-active antibacterial surfaces play a vital role in preventing bacterial contamination of artificial surfaces. In the past, numerous researches have been focused on antibacterial surfaces comprising of antifouling upper-layer and antibacterial sub-layer. In this work, we demonstrate a reversed surface structure which integrate antibacterial upper-layer and antifouling sub-layer. These surfaces are prepared by simply casting gemini quaternary ammonium salt waterborne polyurethanes (GWPU) and their blends. Due to the high interfacial energy of gemini quaternary ammonium salt (GQAS), chain segments containing GQAS can accumulate at polymer/air interface to form an antibacterial upper-layer spontaneously during the film formation. Meanwhile, the soft segments composed of polyethylene glycol (PEG) formed the antifouling sub-layer. Our findings indicate that the combination of antibacterial upper-layer and antifouling sub-layer endow these surfaces strong, long-lasting antifouling and contact-active antibacterial properties, with a more than 99.99% killing efficiency against both gram-positive and gram-negative bacteria attached to them.
Project description:Quaternary ammonium amphiphiles are a class of compounds with a wide range of commercial and industrial uses. In the pharmaceutical field, the most common quaternary ammonium surfactant is benzalkonium chloride (BAC), which is employed as a preservative in several topical formulations for ocular, skin, or nasal application. Despite the broad antimicrobial activity against Gram-positive and Gram-negative bacteria, as well as fungi and small enveloped viruses, safety concerns regarding its irritant and cytotoxic effect on epithelial cells still remain. In this work, quaternary ammonium derivatives of leucine esters (C10, C12 and C14) were synthesised as BAC analogues. These cationic surfactants were characterised in terms of critical micelle concentration (CMC, by tensiometry), cytotoxicity (MTS and LDH assays on the Caco-2 and Calu-3 cell lines) and antimicrobial activity on the bacterial species Staphylococcus aureus and Enterococcus faecalis among the Gram-positives, Escherichia coli and Pseudomonas aeruginosa among the Gram-negatives and the yeast Candida albicans. They showed satisfactory surface-active properties, and a cytotoxic effect that was dependent on the length of the hydrophobic chain. Lower minimum inhibiting concentration (MIC) values were calculated for C14-derivatives, which were comparable to those calculated for BAC toward Gram-positive bacteria and slightly higher for Gram-negative bacteria and C. albicans. Thus, the synthesised leucine-based quaternary ammonium cationic surfactants can potentially find application as promising surface-active compounds with antimicrobial activity.
Project description:Combating bacterial pathogens has become a global concern, especially the emergence of drug-resistant bacteria have made conventional antibiotics lose their efficiency. This grim situation suggests the necessity to explore novel antibacterial agents with favorable safety and strong antibacterial activity. Here, we took the advantage of quaternary ammonium compounds and synthesized a long-chain high-molecular organic bis-quaternary ammonium salt (BQAS) with a broad-spectrum bactericidal activity through a facile one-pot reaction. The bactericidal effect of BQAS was evaluated by two bacterial human pathogens: Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive), which are the major cause of diarrheal infections in children and adults. Our experimental results indicate that the bactericidal activity of BQAS is linked to the strong contact between the positively charged quaternary ammonium groups and the bacterial cells, thus leading to a temporary and locally high concentration of reactive oxygen species, which subsequently triggers oxidative stress and membrane damage in the bacteria. This mechanism was further confirmed by several assays, such as the membrane permeabilization assay, fluorescent-based cell live/dead test, scanning electron microscopy, transmission electron microscopy, together with the lactate dehydrogenase release assay, which all indicated that BQAS induced damage to the cytoplasmic membrane and the leakage of intracellular fluid containing essential molecules. The excellent bactericidal activity of BQAS suggests its great application potential as a promising candidate against the rapid emergence of drug-resistant bacterial pathogens.
Project description:The antibacterial effects of quaternary ammonium resins (QARs) have been reported for decades, but there are few practical applications because of limited improvements in bactericidal capacity and the absence of an efficient antibacterial-indicating parameter. An in-situ determination method of surficial N+ groups for QARs, defined as surficial N+ charge density, was first established to merely quantify the exposed surficial quaternary ammonium groups (QAs). The mechanism of the new method depends on the tetraphenylboron sodium standard solution (TS), which is a colloidal solution with high steric hindrance, making it difficult to permeate into QARs and further react with the inner QAs. The results showed that the antibacterial efficacy of QARs correlates with the surficial N+ charge density with R2 > 0.95 (R2 of 0.97 for Escherichia coli, R2 of 0.96 for Staphylococcus aureus) but not with the strong-base group exchange capacity or zeta potential. Furthermore, the surficial N+ charge density was demonstrated efficient to indicate the antibacterial capacities against both gram-negative and gram-positive bacteria for commercial QARs, including acrylic, styrene and pyridine resin skeletons, especially for the QARs with similar skeletons and similar QAs. Based on the finding that the bactericidal groups merely involve the surficial QAs of QARs, this study proposes a new direction for improving the antibacterial capacity by enriching the surficial QAs and enhancing the bactericidal property of these surficial QAs, and provides a practicable synthesis with two-step quaternization.
Project description:A new class of fused quinazolines has been designed and synthesized via copper-catalyzed Ullmann type C-N coupling followed by intramolecular cross-dehydrogenative coupling reaction in moderate to good yields. The synthesized compounds were tested for in vitro antibacterial activity against three Gram negative (Escherichia coli, Pseudomonas putida, and Salmonella typhi) and two Gram positive (Bacillus subtilis, and Staphylococcus aureus) bacteria. Among all tested compounds, 8ga, 8gc, and 8gd exhibited promising minimum inhibitory concentration (MIC) values (4-8 ?g/mL) for all bacterial strains tested as compared to the positive control ciprofloxacin. The synthesized compounds were also evaluated for their in vitro antifungal activity against Aspergillus niger and Candida albicans and compounds 8ga, 8gc, and 8gd having potential antibacterial activity also showed pronounced antifungal activity (MIC values 8-16 ?g/mL) against both strains. The bactericidal assay by propidium iodide and live-dead bacterial cell screening using a mixture of acridine orange/ethidium bromide (AO/Et·Br) showed considerable changes in the bacterial cell membrane, which might be the cause or consequence of cell death. Moreover, the hemolytic activity for most potent compounds (8ga, 8gc, and 8gd) showed their safety profile toward human blood cells.
Project description:A series of 108 novel quaternary bis-ammonium pyridoxine derivatives carrying various substituents at the quaternary nitrogen's and acetal carbon was synthesized. Thirteen compounds exhibited antibacterial and antifungal activity (minimum inhibitory concentration (MIC) 0.25-16 µg/mL) comparable or superior than miramistin, benzalkonium chloride, and chlorhexidine. A strong correlation between the lipophilicity and antibacterial activity was found. The most active compounds had logP values in the range of 1-3, while compounds with logP > 6 and logP < 0 were almost inactive. All active compounds demonstrated cytotoxicity comparable with miramistin and chlorhexidine on HEK-293 cells and were three-fold less toxic when compared to benzalkonium chloride. The antibacterial activity of leading compound 5c12 on biofilm-embedded Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli or Pseudomonas aeruginosa was comparable or even higher than that of the benzalkonium chloride. In vivo 5c12was considerably less toxic (LD50 1705 mg/kg) than benzalkonium chloride, miramistine, and chlorhexidine at oral administration on CD-1 mice. An aqueous solution of 5c12 (0.2%) was shown to be comparable to reference drugs efficiency on the rat's skin model. The molecular target of 5c12 seems to be a cellular membrane as other quaternary ammonium salts. The obtained results make the described quaternary bis-ammonium pyridoxine derivatives promising and lead molecules in the development of the new antiseptics with a broad spectrum of antimicrobial activity.
Project description:Antibiotic adjuvant therapy represents an exciting opportunity to enhance the activity of clinical antibiotics by co-dosing with a secondary small molecule. Successful adjuvants decrease the concentration of antibiotics used to defeat bacteria, increase activity (in some cases introducing activity against organisms that are drug resistant), and reduce the frequency at which drug-resistant bacteria emerge. We report that 5-alkyloxytryptamines are a new class of broad-spectrum antibacterial agents with exciting activity as antibiotic adjuvants. We synthesized 5-alkyloxytryptamine analogs and found that an alkyl chain length of 6-12 carbons and a primary ammonium group are necessary for the antibacterial activity of the compounds, and an alkyl chain length of 6-10 carbons increased the membrane permeability of Gram-positive and Gram-negative bacteria. Although several of the most potent analogs also have activity against the membranes of human embryonic kidney cells, we demonstrate that below the minimum inhibitory concentration (MIC)-where mammalian cell toxicity is low-these compounds may be successfully used as adjuvants for chloramphenicol, tetracycline, ciprofloxacin, and rifampicin against clinical strains of Salmonella typhimurium, Acinetobacter baumannii and Staphylococcus aureus, reducing MIC values by as much as several logs.
Project description:A series of novel quaternary ammonium 4-deoxypyridoxine derivatives was synthesized. Two compounds demonstrated excellent activity against a panel of Gram-positive methicillin-resistant S. aureus strains with MICs in the range of 0.5-2??g/mL, exceeding the activity of miramistin. At the same time, both compounds were inactive against the Gram-negative E. coli and P. aeruginosa strains. Cytotoxicity studies on human skin fibroblasts and embryonic kidney cells demonstrated that the active compounds possessed similar toxicity with benzalkonium chloride but were slightly more toxic than miramistin. SOS-chromotest in S. typhimurium showed the lack of DNA-damage activity of both compounds; meanwhile, one compound showed some mutagenic potential in the Ames test. The obtained results make the described chemotype a promising starting point for the development of new antibacterial therapies.
Project description:A series of water-soluble cationic chitosan derivatives were prepared by chemoselective functionalization at the amino group of five different parent chitosans having varying degrees of acetylation and molecular weight. The quaternary moieties were introduced at different alkyl spacer lengths from the polymer backbone (C-0, C-2 and C-6) with the aid of 3,6-di-O-tert-butyldimethylsilyl protection of the chitosan backbone, thus allowing full (100%) substitution of the free amino groups. All of the derivatives were characterized using 1H-NMR, 1H-1H COSY and FT-IR spectroscopy, while molecular weight was determined by GPC. Antibacterial activity was investigated against Gram positive S. aureus and Gram negative E. coli. The relationship between structure and activity/toxicity was defined, considering the effect of the cationic group's structure and its distance from the polymer backbone, as well as the degree of acetylation within a molecular weight range of 7-23 kDa for the final compounds. The N,N,N-trimethyl chitosan with 100% quaternization showed the highest antibacterial activity with moderate cytotoxicity, while increasing the spacer length reduced the activity. Trimethylammoniumyl quaternary ammonium moieties contributed more to activity than 1-pyridiniumyl moieties. In general, no trend in the antibacterial activity of the compounds with increasing molecular weight or degree of acetylation up to 34% was observed.
Project description:The fabrication of electrospun composite polyurethane fibers capable of dual-action antibacterial dendrimer release is reported. Generation 4 (G4) poly(amidoamine) dendrimers were functionalized with octyl alkyl chain or quaternary ammonium (QA) moieties followed by modification of the resulting secondary amines with N-diazeniumdiolate nitric oxide (NO) donors to produce dual-action antibacterial dendrimers. Control and NO-releasing dendrimers were doped into polyurethane solutions prior to electrospinning of the polymer to yield well-defined dendrimer-doped composite polyurethane fibers. The fiber mats were semi-porous (?30% porosity) and exhibited high water uptake (>100% relative to fiber mass). Dendrimer- and NO-release characteristics (rates and totals) were dependent on the dendrimer modification and polyurethane composition, with total dendrimer- and NO-release amounts ranging from 10 - 80 ?g/mg and 0.027 - 0.072 ?mol NO/mg, respectively. The antibacterial action of the fibers was evaluated against Gram-negative and Gram-positive bacterial strains. Nitric oxide-releasing fibers demonstrated broad-spectrum bactericidal action at short (2 h) and long (24 h) timescales.