Novel carbazole-oxadiazoles as potential Staphylococcus aureus germicides

Bacterial cell death to overcome drug resistance with multitargeting bis-naphthalimides as potent antibacterial agents against Enterococcus faecalis

The increasing frequency of drug-resistant pathogens poses serious health issues to humans around the globe, leading to the development of new antibacterial agents to conquer drug resistance and bacterial infections. In view of this, we have synthesized a series of bis-naphthalimides to respond to awful drug resistance. Bioactivity assay and structure-activity relationship disclosed that compounds 5d and 5o exhibit potent antibacterial activity against E. faecalis, outperforming the marketed antibiotics. These drug candidates not only inhibit the biofilm formation of E. faecalis but also display rapid bactericidal properties, thus delaying the development of drug resistance within 20 passages. To explore the mechanism of antibacterial activity against E. faecalis, biofunctional examination was carried out which unveiled that 5d and 5o effectively disrupt bacterial cell membranes, causing the leakage of cytoplasmic contents and metabolic activity loss. Concurrently, 5d and 5o effectively intercalate with DNA to block DNA replication, causing the build-up of excessive reactive oxygen species and inhibiting the glutathione activity, ultimately leading to oxidative damage of E. faecalis and cell death. In addition, these compounds readily bind with HSA with a high binding constant, indicating that these drug candidates could be easily delivered to the target site. The above finding manifested that these newly synthesized bis-naphthalimides with multitargeting antibacterial properties offer a new prospect to overcome drug resistance.

Discovery of indolylacryloyl-derived oxacins as novel potential broad-spectrum antibacterial candidates

The emergence of serious bacterial resistance towards clinical oxacins poses a considerable threat to global public health, necessitating the development of novel structural antibacterial agents. Seven types of novel indolylacryloyl-derived oxacins (IDOs) were designed and synthesized for the first time from commercial 3,4-difluoroaniline via an eight-step procedure. The synthesized compounds were characterized by modern spectroscopic techniques. All target molecules were evaluated for antimicrobial activities. Most of the prepared IDOs showed a broad antibacterial spectrum and strong activities against the tested strains, especially ethoxycarbonyl IDO 10d (0.25-0.5 μg/mL) and hydroxyethyl IDO 10e (0.25-1 μg/mL) exhibited much superior antibacterial efficacies to reference drug norfloxacin. These highly active IDOs also displayed low hemolysis, cytotoxicity and resistance, as well as rapid bactericidal capacity. Further investigations indicated that ethoxycarbonyl IDO 10d and hydroxyethyl IDO 10e could effectively reduce the exopolysaccharide content and eradicate the formed biofilm, which might delay the development of drug resistance. Preliminary exploration of the antibacterial mechanism revealed that active IDOs could not only destroy membrane integrity, resulting in changes in membrane permeability, but also promote the accumulation of reactive oxygen species, leading to the production of malondialdehyde and decreased bacterial metabolism. Moreover, they exhibited the capability to bind with DNA and DNA gyrase, forming supramolecular complexes through various noncovalent interactions, thereby inhibiting DNA replication and causing bacterial death. All the above results suggested that the newly developed indolylacryloyl-derived oxacins should hold great promise as potential multitargeting broad-spectrum antibacterial candidates to overcome drug resistance.

Novel aminothiazoximone-corbelled ethoxycarbonylpyrimidones with antibiofilm activity to conquer Gram-negative bacteria through potential multitargeting effects

The emergence of drug-resistant microorganisms threatens human health, and it is usually exacerbated by the formation of biofilm, which forces the development of new antibacterial agents with antibiofilm activity. In this work, a novel category of aminothiazoximone-corbelled ethoxycarbonylpyrimidones (ACEs) was designed and synthesized, and some of the prepared ACEs showed potent bioactivity against the tested bacteria. In particular, imidazolyl ACE 6c showed better inhibitory activity towards Acinetobacter baumannii and Escherichia coli with MIC values both of 0.0066 mmol/L than norfloxacin. It was also revealed that imidazolyl ACE 6c not only possessed inconspicuous hemolytic rate and cytotoxicity, low drug resistance and no risk of penetrating the blood-brain barrier, but also exhibited obvious biofilm inhibition and eradication activities. The preliminary mechanism research suggested that imidazolyl ACE 6c could induce metabolic dysfunction by deactivating lactate dehydrogenase and promote the accumulation of reactive oxygen species to decrease the reduced glutathione and ultimately cause oxidative damage in bacteria. Furthermore, ACE 6c was also found that could insert into DNA to form the supramolecular complex of 6c-DNA and trigger cell death. The multidimensional effect might promote bacterial cell rupture, leading to the leakage of intracellular content. These findings manifested that novel imidazolyl ACE 6c as a potential multitargeting antibacterial agent with potent antibiofilm activity could provide new possibility for the treatment of refractory biofilm-intensified bacterial infections.

New broad-spectrum and potent antibacterial agents with dual-targeting mechanism: Promoting FtsZ polymerization and disrupting bacterial membranes

The emergence of multidrug-resistant bacteria and the slow development of new antibacterial agents have led to a growing global health crisis. Here, we identified an antibacterial agent possessing 1-methyl-2,5-diphenylpyridin-1-ium core, MA220607, with a dual-targeting mechanism of action (MOA), which exhibited effective killing activity against both Gram-positive (MIC = 0.062-2 μg/mL) and Gram-negative bacteria (MIC = 0.5-4 μg/mL). Moreover, our study revealed that MA220607 could block the formation of bacterial biofilm, which might be the reason for low frequency of resistance. MOA studies showed that MA220607 not only promoted FtsZ protein polymerization, but also increased the permeability of bacterial membranes and altered their proton gradients. In addition, MA220607 had low hemolytic toxicity and could significantly inhibit the growth of bacteria in mice. Molecular dynamics simulations demonstrated that MA220607 could block the transition from the tense (T) to relaxed (R) state of FtsZ protein, thereby perturbing the stepping mechanism of FtsZ protein. Overall, our findings suggest that integrating the dual mechanisms targeting FtsZ protein and cell membranes of bacteria into a single scaffold represents a promising direction for the development of new antibacterial agents.

Anti-inflammatory and Antimicrobial Potential of 1, 3, 4-oxadiazoles and its Derivatives: A Review

1, 3, 4-oxadiazole and its derivatives have significant anti-inflammatory and antimicrobial property. Their precise mechanism of action is not known but it is postulated that they act by inhibiting the biosynthesis of certain prostaglandins. 1, 3, 4-oxadiazoles are a class of heterocyclic compounds with wide variety of biological and pharmacological activities. They have been reported to possess analgesic, antimicrobial, antipyretic and anti-inflammatory properties. These compounds are also active against a number of other inflammatory conditions such as arthritis, gout etc. A wide variety of these compounds have been synthesized and some of them are under clinical trials. In this review article, anti-inflammatory and antimicrobial activity of the 1, 3, 4- oxadiazole shall be discussed.

Benzopyrone-mediated quinolones as potential multitargeting antibacterial agents

A new type of benzopyrone-mediated quinolones (BMQs) was rationally designed and efficiently synthesized as novel potential antibacterial molecules to overcome the global increasingly serious drug resistance. Some synthesized BMQs effectively suppressed the growth of the tested strains, outperforming clinical drugs. Notably, ethylidene-derived BMQ 17a exhibited superior antibacterial potential with low MICs of 0.5-2 μg/mL to clinical drugs norfloxacin, it not only displayed rapid bactericidal performance and inhibited bacterial biofilm formation, but also showed low toxicity toward human red blood cells and normal MDA-kb2 cells. Mechanistic investigation demonstrated that BMQ 17a could effectually induce bacterial metabolic disorders and promote the enhancement of reactive oxygen species to disrupt the bacterial antioxidant defense system. It was found that the active molecule BMQ 17a could not only form supramolecular complex with lactate dehydrogenase, which disturbed the biological functions, but also effectively embed into calf thymus DNA, thus affecting the normal function of DNA and achieving cell death. This work would provide an insight into developing new molecules to reduce drug resistance and expand antibacterial spectrum.

Identification of unique indolylcyanoethylenyl sulfonylanilines as novel structural scaffolds of potential antibacterial agents

The increasing incidence of antibiotic resistance has forced the development of unique antimicrobials with novel multitargeting mechanisms to combat infectious diseases caused by multidrug-resistant pathogens. Structurally unique indolylcyanoethylenyl sulfonylanilines (ISs) were exploited as novel promising antibacterial agents to confront stubborn drug resistance. Some prepared ISs possessed favorable bacteriostatic action towards the tested bacteria. Especially, hydroxyethyl IS 14a exerted 8-fold more potent inhibitory efficacy against multidrug-resistant A. baumannii and E. coli 25922 with the low MIC of 0.5 μg/mL than norfloxacin, and showed low cell toxicity and rapid bactericidal property. Moreover, this compound also possessed obvious effect of eradicating bacterial biofilm, which could effectually relieve the development of drug resistance. A preliminary assessment of the antibacterial mechanism indicated that compound 14a could disintegrate membrane integrity leading to the leakage of intracellular protein, inactivation of lactate dehydrogenase and metabolism inhibition. Hydroxyethyl IS 14a mediated the accumulation of excess reactive oxygen species, which further contributed to reducing glutathione, resulting in oxidative damage to bacteria. Furthermore, IS 14a could intercalate into DNA to hinder the biological function of DNA. Quantum chemical study disclosed that IS 14a with the lowest energy gap was conducive to displaying high bioactivity. These findings demonstrated that hydroxyethyl IS 14a as a prospective antimicrobial candidate for combating A. baumannii and E. coli 25922 would be a promising starting point.

Antimicrobial activity of natural and semi-synthetic carbazole alkaloids

Since the first natural carbazole alkaloid, murrayanine, was isolated from Mwraya Spreng, carbazole alkaloid derivatives have been widely concerned for their anti-tumor, anti-viral and anti-bacterial activities. In recent decades, a growing body of data suggest that carbazole alkaloids and their derivatives have different biological activities. This is the first comprehensive description of the antifungal and antibacterial activities of carbazole alkaloids in the past decade (2012-2022), including natural and partially synthesized carbazole alkaloids in the past decade. Finally, the challenges and problems faced by this kind of alkaloids are summarized. This paper will be helpful for further exploration of this kind of alkaloids.

Antimicrobial Activity and Toxicity of Newly Synthesized 4-[4-(benzylamino)butoxy]-9H-carbazole Derivatives

One of the main challenges of medicinal chemistry is the search for new substances with antimicrobial potential that could be used in the fight against pathogenic microorganisms. Therefore, the antimicrobial activity of newly synthesized compounds is still being investigated. Carbazole-containing compounds appear to be promising antibacterial, antifungal, and antiviral agents. The aim of this study was to examine the antimicrobial potential and toxicity of newly synthesized isomeric fluorinated 4-[4-(benzylamino)butoxy]-9H-carbazole derivatives. Their antimicrobial activity against bacteria and fungi was tested according to CLSI guidelines. Similarly to previously studied carbazole-containing compounds, the tested derivatives showed the ability to effectively inhibit the growth of Gram-positive bacteria. The addition of carbazole derivatives 2, 4, and 8 at the concentration of 16 µg/mL caused the inhibition of S. aureus growth by over 60%. The MIC value of compounds 2-5 and 7-10 was 32 µg/mL for Staphylococcus strains. Gram-negative strains of E. coli and P. aeruginosa were found to be more resistant to the tested carbazole derivatives. E. coli cells treated with compounds 3 and 8 at a concentration of 64 µg/mL resulted in a greater-than-40% reduction in bacterial growth. In the case of the P. aeruginosa strain, all compounds in the highest concentration that we tested limited growth by 35-42%. Moreover, an over-60% inhibition of fungal growth was observed in the cultures of C. albicans and A. flavus incubated with 64 µg/mL of compounds 2 or 7 and 1 or 4, respectively. The hemolysis of red blood cells after their incubation with the tested carbazole derivatives was in the range of 2-13%. In the case of human fibroblast cells, the toxicity of the tested compounds was higher. Derivative 1, functionalized with fluorine in position 2 and its hydrobromide, was the least toxic. The obtained results indicated the antimicrobial potential of the tested 4-[4-(benzylamino)butoxy]-9H-carbazole derivatives, especially against S. aureus strains; therefore, it is worth further modifying these structures, in order to enhance their activity against pathogenic microorganisms.

Synthesis and antimicrobial activity of new series of thiazoles, pyridines and pyrazoles based on coumarin moiety

Microbial infections are currently a widespread disease in hospitals and community health centres and are a major cause of death worldwide. In pursuit of searching new antimicrobial agents, coumarin linked to thiazoles, pyridines and pyrazoles have been developed and evaluated for their antimicrobial properties against two Gram + bacteria, two Gram - bacteria as well as two fungi. Some of the prepared coumarins displayed high to moderate activity against the tested microorganisms with respect to the reference drugs. However, compound 3 exhibited antimicrobial effect equal to the reference drug Ciprofloxacin for Gram - baceria Enterobacter cloacae. Compound 12 was found to be the most potent compound against Bacillus pumilis with MIC of 7.69 (µmol/ml). Compounds 3, 4 and 12 showed remarkable activity against Streptococcus faecalis with MIC of 14.34, 3.67 and 15.36 (µmol/ml), respectively. Regarding Escherichia coli, most compounds recorded high to moderate MIC values (4.73-45.46 µmol/ml). Moreover, in case of E. cloacae compound 9 was the most potent compound with MIC value of 22.76 (µmol/ml).

Membrane-active substituted triazines as antibacterial agents against Staphylococcus aureus with potential for low drug resistance and broad activity

A library of new naphthalimide-triazine analogues was synthesized as broad-spectrum antibacterial agents to overcome drug resistance. Bioactivity assay reveals that derivative 8e, with benzylamine in its structure, exhibits strong antibacterial properties against multi-drug resistance Staphylococcus aureus at a concentration of 1.56 μg/ml. It was also found to be better than chloromycin and amoxicillin. The active compound 8e efficiently inhibits the development of drug resistance within 11 passages. In addition, compound 8e inhibits the formation of biofilms in S. aureus and acts rapidly in bactericidal efficacy. Furthermore, mechanistic studies reveal that compound 8e effectively destroys the cytoplasmic membrane of bacteria, leading to leakage of intercellular protein content and loss in metabolic activity. Compound 8e binds to HSA readily with a binding constant of 1.32 × 10⁵ M^-1, indicating that the compound could be delivered to the target site effectively. Compound 8e can also form a supramolecular complex with DNA to obstruct DNA replications. These results suggest that analogue 8e could be further developed as a potential antibacterial agent. Furthermore, the cytotoxicity of all the synthesized compounds was evaluated against 60 human cancer cell lines to test their potential for anticancer agents.

Novel Thiazolylketenyl Quinazolinones as Potential Anti-MRSA Agents and Allosteric Modulator for PBP2a

Bacterial infections caused by methicillin-resistant Staphylococcus aureus have seriously threatened public health. There is an urgent need to propose an existing regimen to overcome multidrug resistance of MRSA. A unique class of novel anti-MRSA thiazolylketenyl quinazolinones (TQs) and their analogs were developed. Some synthesized compounds showed good bacteriostatic potency. Especially TQ 4 was found to exhibit excellent inhibition against MRSA with a low MIC of 0.5 μg/mL, which was 8-fold more effective than norfloxacin. The combination of TQ 4 with cefdinir showed stronger antibacterial potency. Further investigation revealed that TQ 4, with low hemolytic toxicity and low drug resistance, was not only able to inhibit biofilm formation but also could reduce MRSA metabolic activity and showed good drug-likeness. Mechanistic explorations revealed that TQ 4 could cause leakage of proteins by disrupting membrane integrity and block DNA replication by intercalated DNA. Furthermore, the synergistic antibacterial effect with cefdinir might be attributed to TQ 4 with the ability to induce PBP2a allosteric regulation of MRSA and further trigger the opening of the active site to promote the binding of cefdinir to the active site, thus inhibiting the expression of PBP2a, thereby overcoming MRSA resistance and significantly enhancing the anti-MRSA activity of cefdinir. A new strategy provided by these findings was that TQ 4, possessing both excellent anti-MRSA activity and allosteric effect of PBP2a, merited further development as a novel class of antibacterial agents to overcome increasingly severe MRSA infections.

Thiazolyl hydrazineylidenyl indolones as unique potential multitargeting broad-spectrum antimicrobial agents

The emergence of pathogenic and drug-resistant microorganisms seriously threatens public safety. This work constructed a unique type of thiazolyl hydrazineylidenyl indolones (THIs) to combat global microbial multidrug-resistance. Bioactive evaluation discovered that some target THIs displayed much superior antimicrobial efficacy than clinical chloromycetin, norfloxacin, cefdinir or fluconazole against the tested strains. Eminently, butyl THI 6c displayed a broad antimicrobial spectrum with low MICs of 0.25-1 μg/mL. The highly active THI 6c not only showed low cytotoxicity and hemolysis, rapidly bactericidal ability, good antibiofilm activity and promising pharmacokinetic properties, but also could significantly impede the development of bacterial resistance. Preliminary exploration of antibacterial mechanism revealed that THI 6c could effectively penetrate the cell membrane of MRSA and embed DNA to form 6c‒DNA supramolecular complex and thus hinder DNA replication. Moreover, THI 6c could reduce cell metabolic activity, which might be attributed to the fact that THI 6c could target the pyruvate kinase of MRSA and interfere with the function of the enzyme. These results provided powerful information for further developing thiazolyl hydrazineylidenyl indolones as new broad-spectrum antimicrobial agents.

Comprehensive Insights into Medicinal Research on Imidazole-Based Supramolecular Complexes

The electron-rich five-membered aromatic aza-heterocyclic imidazole, which contains two nitrogen atoms, is an important functional fragment widely present in a large number of biomolecules and medicinal drugs; its unique structure is beneficial to easily bind with various inorganic or organic ions and molecules through noncovalent interactions to form a variety of supramolecular complexes with broad medicinal potential, which is being paid an increasing amount of attention regarding more and more contributions to imidazole-based supramolecular complexes for possible medicinal application. This work gives systematical and comprehensive insights into medicinal research on imidazole-based supramolecular complexes, including anticancer, antibacterial, antifungal, antiparasitic, antidiabetic, antihypertensive, and anti-inflammatory aspects as well as ion receptors, imaging agents, and pathologic probes. The new trend of the foreseeable research in the near future toward imidazole-based supramolecular medicinal chemistry is also prospected. It is hoped that this work provides beneficial help for the rational design of imidazole-based drug molecules and supramolecular medicinal agents and more effective diagnostic agents and pathological probes.

Degradation of imidacloprid and acetamiprid in tea (Camellia sinensis) infusion by ultraviolet light irradiation

The degradation of imidacloprid and acetamiprid in tea infusion by ultraviolet (UV) light irradiation was investigated in this study. Results showed that the influence of UV light irradiation on the quality of tea infusion was controllable and UV light irradiation was effective on the degradation of both pesticides. The maximum removal rates were 75.2% for imidacloprid and 17.6% for acetamiprid after irradiation (650 µW/cm,² 120 min). The degradation of both pesticides followed the first-order kinetics model. Three degradation products were identified for imidacloprid and one for acetamiprid based on liquid chromatography-tandem mass spectrometry analysis. The degradation pathway of imidacloprid involved in the cleavage of C-C bond with the loss of nitro group followed by the hydrogenation, oxidation and hydrolysis, while the degradation of acetamiprid involved in the oxidation at the chlorine atom with the bonding of C atoms at positions 1 and 4 on the pyridine ring. Simultaneously, the toxicity of both pesticides was mitigated by UV light irradiation according to LO2 cell toxicity evaluation. The study provided a low-cost and effective way to reduce imidacloprid and acetamiprid from tea infusion, and it has the potential to be applied to the ready-to drink tea beverage production in industrial scale.

Benzenesulfonyl thiazoloimines as unique multitargeting antibacterial agents towards Enterococcus faecalis

New efficient antimicrobial agents are urgently needed to combat invasive multidrug-resistant pathogens infections. Structurally unique benzenesulfonyl thiazoloimines (BSTIs) were exploited as novel potential antibacterial victors to confront terrific drug resistance. Some developed BSTIs exerted effectively antimicrobial efficacy against the tested strains. Notably, 2-pyridyl BSTI 14d exhibited good antibacterial activity against E. faecalis with MIC value of 1 μg/mL, which was superior to sulfathiazole and norfloxacin. The most active compound 14d not only showed rapid bactericidal properties and impeded E. faecalis biofilm formation to effectually relieve the development of drug resistance, but also performed low toxicity toward human red blood cells, human normal squamous epithelial cells and human non-neoplastic colon epithelial cells. Mechanistic investigation demonstrated that molecule 14d could exert efficient membrane destruction leading to the leakage of intracellular materials and metabolism inhibition, cause oxidative damage of E. faecalis through accumulation of excess reactive oxygen species and reduction of glutathione activity, and intercalate into DNA to hinder replication of DNA. Molecular docking indicated that the formation of 14d-dihydrofolate synthetase supramolecular complex could hinder the function of this enzyme. ADME analysis displayed that compound 14d possessed promising pharmacokinetic properties. These findings suggested that the newly developed benzenesulfonyl thiazoloimines with multitargeting antibacterial potential provided a new possibility for evading resistance.

New Efforts toward Aminothiazolylquinolones with Multitargeting Antibacterial Potential

New antibacterial 3-(aminothiazolyl)quinolones (ATQs) were designed and efficiently synthesized to counteract the growing multidrug resistance in animal husbandry. Bioactive assays manifested that N,N-dicyclohexylaminocarbonyl ATQ 10e and methyl ATQ 17a, respectively, showed better antibacterial behavior against Staphylococcus aureus ATCC 29213 and Pseudomonas aeruginosa than reference drug norfloxacin. Notably, highly active ATQ 17a with low hemolysis, negligible mammalian cytotoxicity, and good pharmacokinetic properties displayed low trends to induce resistance and synergistic combinations with norfloxacin. Preliminary mechanism exploration implied that representative ATQ 17a could inhibit the formation of biofilms and destroy bacterial membrane integrity, further binding to intracellular DNA and DNA gyrase to hinder bacterial DNA replication. ATQ 17a could also induce the production of excess reactive oxygen species and reduce bacterial metabolism to accelerate bacterial death. These results provided a promise for 3-(aminothiazolyl)quinolones as new potential multitargeting antibacterial agents to treat bacterial infection of animals.

Identification of Novel Antifungal Skeleton of Hydroxyethyl Naphthalimides with Synergistic Potential for Chemical and Dynamic Treatments

The invasion of pathogenic fungi poses nonnegligible threats to the human health and agricultural industry. This work exploited a family of hydroxyethyl naphthalimides as novel antifungal species with synergistic potential of chemical and dynamic treatment to combat the fungal resistance. These prepared naphthalimides showed better antifungal potency than fluconazole towards some tested fungi including Aspergillus fumigatus, Candida tropicalis and Candida parapsilosis 22019. Especially, thioether benzimidazole derivative 7f with excellent anti-Candida tropicalis efficacy (MIC = 4 μg/mL) possessed low cytotoxicity, safe hemolysis level and less susceptibility to induce resistance. Biochemical interactions displayed that 7f could form a supramolecular complex with DNA to block DNA replication, and constitute a biosupermolecule with cytochrome P450 reductase (CPR) from Candida tropicalis to hinder CPR biological function. Additionally, 7f presented strong lipase affinity, which facilitated its permeation into cell membrane. Moreover, 7f with dynamic antifungal potency promoted the production and accumulation of reactive oxygen species (ROS) in cells, which destroyed the antioxidant defence system, led to oxidative stress with lipid peroxidation, loss of glutathione, membrane dysfunction and metabolic inactivation, and eventually caused cell death. The chemical and dynamic antifungal synergistic effect initiated by hydroxyethyl naphthalimides was a reasonable treatment window for prospective development.

An unanticipated discovery of novel naphthalimidopropanediols as potential broad-spectrum antibacterial members

Constructing a new antibacterial structural framework is an effective strategy to combat drug resistance. This work discovered a class of naphthalimidopropanediols (NIOLs) as a novel structural type of potential broad-spectrum antibacterial agents. Especially, NIOLs 9u, 12i, 15 against Staphylococcus aureus and NIOLs 9l, 13a against Pseudomonas aeruginosa showed excellent inhibitory activities, and they displayed high membrane selectivity from an electrostatic distinction on the membranes between bacteria and mammalian cells. These highly active NIOLs could effectually inhibit the bacterial growths, and relieve the resistance developments. Moreover, the facts of membrane depolarization, outer/inner membrane permeabilization and leakage of intracellular materials, demonstrated that these NIOLs could target and destroy the S. aureus or P. aeruginosa membranes. In particular, they could disrupt the antioxidant defense systems of S. aureus or P. aeruginosa through up-regulation of reactive oxygen species. Simultaneously, they could render the metabolic inactivation of the tested strains, and eradicate the formed biofilms and efficiently kill the strains within the biofilms. The in vitro and in vivo cytotoxicity assay indicated that these compounds possessed low toxicity. These findings of novel NIOLs as potential broad-spectrum antibacterial members provided a bright hope for conquering drug resistance.

A New Discovery of Unique 13-(Benzimidazolylmethyl)berberines as Promising Broad-Spectrum Antibacterial Agents

A new hybridization of berberine and benzimidazoles was performed to produce 13-(benzimidazolylmethyl)berberines (BMB) as potentially broad-spectrum antibacterial agents with the hope of confronting multidrug-resistant bacterial infections in the livestock industry. Some of the newly prepared hybrids showed obvious antibacterial effects against tested strains. Particularly, 13-((1-octyl-benzimidazolyl)methyl)berberine 6f (OBMB-6f) was found to be the most promising compound that not only exerted a strong activity (MIC = 0.25-2 μg/mL) and low cytotoxicity but also possessed a fast bactericidal capacity and low propensity to develop resistance toward Staphylococcus aureus and Escherichia coli even after 26 serial passages. Moreover, OBMB-6f displayed the ability to prevent bacterial biofilm formation at low and high temperatures. The mechanistic exploration revealed that OBMB-6f could significantly disintegrate bacterial membranes, markedly facilitate intracellular ROS generation, and efficiently intercalate into DNA. These results provided a profound insight into BMB against multidrug-resistant bacterial infections in the livestock industry.

Pyrimidine-conjugated fluoroquinolones as new potential broad-spectrum antibacterial agents

Pyrimidine-conjugated fluoroquinolones were constructed to cope with the dreadful resistance. Most of the target pyrimidine derivatives effectively suppressed the growth of the tested strains, especially, 4-aminopyrimidinyl compound 1c showed a broad antibacterial spectrum and low cytotoxicity and exhibited superior antibacterial potency against Enterococcus faecalis with a low MIC of 0.25 μg/mL to norfloxacin and ciprofloxacin. The active compound 1c with fast bactericidal potency could inhibit the formation of biofilms and showed much lower trend for the development of drug-resistance than norfloxacin and ciprofloxacin. Further exploration revealed that compound 1c could prompt ROS accumulations in bacterial cells and interact with DNA to form a DNA-1c complex, thus facilitating bacterial death. ADME analysis indicated that compound 1c possessed favorable drug-likeness and promising pharmacokinetic properties. These results demonstrated that pyrimidine-conjugated fluoroquinolones held hope as potential antibacterial candidates and deserve further study.

New 1,3,4-oxadiazole compound with effective antibacterial and antibiofilm activity against Staphylococcus aureus

Staphylococcus aureus is one of the main aetiological agents causing food-borne diseases. Some strains produce enterotoxins responsible for food poisoning. In addition, they can form biofilms on several surfaces such as plastics, glass and stainless steel making it difficult to eliminate them. The present study evaluated, for the first time, the antibacterial and antibiofilm activities of the synthetic compound LMM6 against S. aureus. The minimum inhibitory concentration was 0·97, 1·95 and 1·95 μg ml^-1 against S. aureus ATCC 25923, S. aureus 629/94 and S. aureus FRI S-6, respectively. The time-kill curves showed that 96 h treatment with LMM6 reduced approximately 4 log CFU per ml at all tested concentrations. Furthermore, LMM6 reduced S. aureus preformed biofilm by approximately 1 log CFU per cm² . During biofilm formation, a reduction of approximately 4 log CFU per cm² was observed. LMM6 also reduced biofilm biomass during (~60%) and after biofilm formation (~25 to 45%), as shown by the crystal violet assay. Based on these results, we conclude that LMM6 exhibits antibacterial and antibiofilm activity and may be an innovative synthetic molecule for controlling S. aureus.

Discovery of novel phenylhydrazone-based oxindole-thiolazoles as potent antibacterial agents toward Pseudomonas aeruginosa

With the soaring of bacterial infection and drug resistance, it is imperative to exploit new efficient antibacterial agents. This work constructed a series of unique phenylhydrazone-based oxindole-thiolazoles to combat monstrous bacterial resistance. Some target molecules showed potent antibacterial activity, among which oxindole-thiolimidazole derived carboxyphenylhydrazone 4e exhibited an 8-fold stronger inhibitory ability than norfloxacin on the growth of P. aeruginosa, with MIC value of 1 μg/mL. Compound 4e with imperceptible hemolysis could hamper bacterial biofilm formation and significantly impede the development of bacterial resistance. Subsequent mechanism studies demonstrated that 4e could destruct bacterial cytoplasmic membrane, causing the leakage of cellular contents (protein and nucleic acid). Moreover, metabolic stagnation and intracellular oxidative stress caused by 4e expedited the death of bacteria. Furthermore, molecule 4e existed supramolecular interactions with DNA to block DNA proliferation. These research results provided a promising light for phenylhydrazone-based oxindole-thiolazoles as novel potential antibacterial agents.

Natural aloe emodin-hybridized sulfonamide aminophosphates as novel potential membrane-perturbing and DNA-intercalating agents against Enterococcus faecalis

The dramatic rise in drug resistance accelerated the desire for new antibacterial agents to safeguard human health. This work constructed a novel type of aloe emodin-hybridized sulfonamide aminophosphates as unique potential antibacterial agents. The biological assay revealed that some target hybrids possessed potent inhibitory activity. Particularly, ethyl aminophosphate-hybridized sulfadiazine aloe emodin 7a (EASA-7a) not only displayed preponderant antibacterial efficiency against drug-resistant E. faecalis at low concentration as 0.25 μg/mL but also possessed strong bacteriostatic capacity and low propensity to develop resistance toward E. faecalis. The weak hemolysis toward human red blood cells and efficient biofilm-disruptive ability further implied the therapeutic potential of EASA-7a. Preliminary studies disclosed that the excellent antibacterial behavior of EASA-7a might be attributed to its capacity to permeate and depolarize the bacterial membrane, as well as promote ROS accumulation and intercalate with DNA. These findings manifested that EASA-7a was worthy of further development to combat life-threatening bacterial infections.

Unique Carbazole-Oxadiazole Derivatives as New Potential Antibiotics for Combating Gram-Positive and -Negative Bacteria

Novel carbazole-oxadiazoles were developed as new potential antibacterial agents to combat dreadful resistance. Some target compounds displayed predominant inhibitory effects on the tested Gram-positive and -negative bacteria, and carbazole-oxadiazoles 5g, 5i-k, 16a-c, and tetrazole analogues 23b-c were found to be efficient in impeding the growth of MRSA and Pseudomonas aeruginosa ATCC 27853 (MICs = 0.25-4 μg/mL). Furthermore, compounds 5g and 23b-c not only possessed rapid bactericidal ability and low tendency to develop resistance but also exhibited low cytotoxic effects toward Hek 293T, HeLa, and red blood cells (RBCs), especially molecule 5g also showed low toxicity in vivo, which showed the therapeutic potential of these compounds. Further exploration indicated that compounds 5g, 5i, and 23b-c could disintegrate the integrity of bacterial cell membranes to leak the cytoplasmic contents, thus exerting excellent antibacterial effects. These facts mean that carbazole-based antibacterial agents might have bright prospects in confronting bacterial infections.

Natural Berberine-derived Azolyl Ethanols as New Structural Antibacterial Agents against Drug-Resistant Escherichia coli

Natural berberine-derived azolyl ethanols as new structural antibacterial agents were designed and synthesized for fighting with dreadful bacterial resistance. Partial target molecules exhibited potent activity against the tested strains, particularly, nitroimidazole derivative 4d and benzothiazole-2-thoil compound 18b, with low cytotoxicity both exerted strong antibacterial activities against multidrug-resistant Escherichia coli at low concentrations as 0.007 and 0.006 mM, respectively. Meanwhile, the active compounds 4d and 18b possessed the ability to rapidly kill bacteria and observably eradicate the E. coli biofilm by reducing exopolysaccharide content to prevent bacterial adhesion, which was conducive to alleviating the development of E. coli resistance. Preliminary mechanistic explorations suggested that the excellent antibacterial potential of molecules 4d and 18b might be attributed to their ability to disintegrate membrane, accelerate ROS accumulation, reduce bacterial metabolism, and intercalate into DNA groove. These results provided powerful information for the further exploitation of natural berberine derivatives against bacterial pathogens.

An unanticipated discovery towards novel naphthalimide corbelled aminothiazoximes as potential anti-MRSA agents and allosteric modulators for PBP2a

Available therapeutic strategies are urgently needed to conquer multidrug resistance of MRSA. A visible effort was guided towards the advancement of novel antibacterial framework of naphthalimide corbelled aminothiazoximes, and desired to assert some insight on the conjunction of individual pharmacophore with distinct biological activities and unique action mechanism. Preliminary assessment displayed that dimethylenediamine derivative 13d presented a wonderful inhibition on MRSA (MIC = 0.5 μg/mL), and showed excellent membrane selectivity (HC₅₀ > 200 μg/mL) from an electrostatic distinction of the electronegative bacterial membranes and the electroneutral mammalian membranes. Moreover, 13d could effectually relieve the development of MRSA resistance. Investigations into explaining the mechanism of anti-MRSA disclosed that 13d displayed strong lipase affinity, which facilitated its permeation into cell membrane, causing membrane depolarization, leakage of cytoplasmic contents and lactate dehydrogenase (LDH) inhibition. Meanwhile, 13d could exert interaction with DNA to hinder biological function of DNA, and disrupt the antioxidant defense system of MRSA through up-regulation of ROS subjected the strain to oxidative stress. In particular, the unanticipated mechanism for naphthalimide corbelled aminothiazoximes that 13d could suppress the expression of PBP2a by inducing allosteric modulation of PBP2a and triggering the open of the active site, was discovered for the first time. These findings of naphthalimide corbelled aminothiazoximes as a small-molecule class of anti-MRSA agents held promise in strategies for treatment of MRSA infections.

Evaluation of the Antimicrobial Potential and Toxicity of a Newly Synthesised 4-(4-(Benzylamino)butoxy)-9H-carbazole

One of the greatest threats to human and animal health is posed by infections caused by drug-resistant bacterial strains. Therefore, newly synthesised substances are tested for their antimicrobial activity. Carbazole derivatives seem to be promising antibacterial agents. This study aimed at investigating the toxicity and activity of newly synthesised, functionalised carbazole derivative 2 (4-(4-(benzylamino)butoxy)-9H-carbazole) against various microorganisms. Its antimicrobial potential against Gram-positive and Gram-negative bacteria, yeast, and filamentous fungi was examined according to CLSI (Clinical and Laboratory Standards Institute) standards. The tested compound was found to efficiently inhibit the growth of Gram-positive strains. The addition of carbazole derivative 2 at the concentration of 30 µg/mL caused inhibition of bacterial growth by over 95%. Moreover, about 50 and 45% limitation of Pseudomonas aeruginosa and Aspergillus flavus growth was observed in the samples incubated with the addition of 20 and 60 µg/mL of the compound, respectively. Its addition to the microbial cultures caused an increase in the permeability of the cellular membrane. Slight haemolysis of red blood cells was observed after 24-h treatment with carbazole derivative 2. On the other hand, human fibroblasts were found to be more sensitive to its effects. The activity of the tested compound indicates a possibility of its further modification in order to obtain effective drugs, especially against drug-resistant staphylococci.

A facile reaction to access novel structural sulfonyl-hybridized imidazolyl ethanols as potential DNA-targeting antibacterial agents

A novel type of sulfonyl-hybridized imidazolyl ethanols as potential DNA-targeting antibacterial agents was constructed via the unique ring-opened reaction of oxiranes by imidazoles for the first time. Some developed target hybrids showed potential antimicrobial potency against the tested microbes. Especially, imidazole derivative 5f could strongly suppressed the growth of MRSA (MIC = 4 μg/mL), which was 2-fold and 16-fold more potent than the positive control sulfathiazole and norfloxacin. This compound exhibited quite low propensity to induce bacterial resistance. Antibacterial mechanism exploration indicated that compound 5f could embed in MRSA DNA to form steady 5f-DNA complex, which possibly hinder DNA replication to exert antimicrobial behavior. Molecular docking showed that molecule 5f could bind with dihydrofolate synthetase through hydrogen bonds. These results implied that imidazole derivative 5f could be served as a promising molecule for the exploration of novel antibacterial candidates.

Natural Berberine-Hybridized Benzimidazoles as Novel Unique Bactericides against Staphylococcus aureus

Natural berberine-hybridized benzimidazoles as potential antibacterial agents were constructed to treat Staphylococcus aureus infection in the livestock industry. Bioassay showed that some new berberine-benzimidazole hybrids exhibited potent antibacterial efficacies, especially, the 2,4-dichlorobenzyl derivative 7d not only showed strong activity against S. aureus ATCC 29213 with the MIC value of 0.006 mM but also effectively eradicated bacterial biofilm and exhibited low toxicity toward mammalian cells. The drug combination experiments showed that compound 7d together with norfloxacin could enhance the antibacterial efficacy. Moreover, the 2,4-dichlorobenzyl derivative 7d did not show obvious propensity to develop bacterial resistance. Preliminary mechanism studies revealed that the active molecule 7d could damage the membrane integrity, stimulate ROS generation, and bind with DNA as well as S. aureus sortase A, thus exerting powerful antibacterial ability. In light of these facts, berberine-benzimidazole hybrid 7d showed a large potentiality as a new bactericide for treating S. aureus in the livestock industry.

Molecular design and preparation of 2-aminothiazole sulfanilamide oximes as membrane active antibacterial agents for drug resistant Acinetobacter baumannii

A series of 2-aminothiazole sulfanilamide oximes were developed as new membrane active antibacterial agents to conquer the microbial infection. Benzoyl derivative 10c was preponderant for the treatment of drug-resistant A. baumannii infection in contrast to norfloxacin and exerted excellent biocompatibility against mammalian cells including erythrocyte and LO2 cell line. Meanwhile, it had ability to eradicate established biofilm to alleviate the resistance burden. Mechanism investigation elucidated that compound 10c was able to disturb the membrane effectively and inhibit lactic dehydrogenase, which led to cytoplasmic content leakage. The cellular redox homeostasis was interfered via the production of reactive oxygen and nitrogen species (RONS), which further contributed to respiratory pathway inactivation and reduction of GSH activity. This work indicated that 2-aminothiazole sulfanilamide oximes could be a promising start for the exploitation of novel antibacterial agents against pathogens.

Discovery of novel purinylthiazolylethanone derivatives as anti-Candida albicans agents through possible multifaceted mechanisms

An unprecedented amount of fungal and fungal-like infections has recently brought about some of the most severe die-offs and extinctions due to fungal drug resistance. Aimed to alleviate the situation, new effort was made to develop novel purinylthiazolylethanone derivatives, which were expected to combat the fungal drug resistance. Some prepared purinylthiazolylethanone derivatives possessed satisfactory inhibitory action towards the tested fungi, among which compound 8c gave a MIC value of 1 μg/mL against C. albicans. The active molecule 8c was able to kill C. albicans with undetectable resistance as well as low hematotoxicity and cytotoxicity. Furthermore, it could hinder the growth of C. albicans biofilm, thus avoiding the occurrence of drug resistance. Mechanism research manifested that purinylthiazolylethanone derivative 8c led to damage of cell wall and membrane disruption, so protein leakage and the cytoplasmic membrane depolarization were observed. On this account, the activity of fungal lactate dehydrogenase was reduced and metabolism was impeded. Meanwhile, the increased levels of reactive oxygen species (ROS) and reactive nitrogen species (RNS) disordered redox equilibrium, giving rise to oxidative damage to fungal cells and fungicidal effect.