Multi-targeting exploration of new 2-aminothiazolyl quinolones: Synthesis, antimicrobial evaluation, interaction with DNA, combination with topoisomerase IV and penetrability into cells

Synthesis and antibacterial medicinal evaluation of carbothioamido hydrazonyl thiazolylquinolone with multitargeting antimicrobial potential to combat increasingly global resistance

The global microbial resistance is a serious threat to human health, and multitargeting compounds are considered to be promising to combat microbial resistance. In this work, a series of new thiazolylquinolones with multitargeting antimicrobial potential were developed through multi-step reactions using triethoxymethane and substituted anilines as start materials. Their structures were confirmed by 1H NMR, 13C NMR and HRMS spectra. Antimicrobial evaluation revealed that some of the target compounds could effectively inhibit microbial growth. Especially, carbothioamido hydrazonyl aminothiazolyl quinolone 8a showed strong inhibitory activity toward drug-resistant Staphylococcus aureus with MIC value of 0.0047 mM, which was 5-fold more active than that of norfloxacin. The highly active compound 8a exhibited negligible hemolysis, no significant toxicity in vitro and in vivo, low drug resistance, as well as rapidly bactericidal effects, which suggested its favorable druggability. Furthermore, compound 8a was able to effectively disrupt the integrity of the bacterial membrane, intercalate into DNA and inhibit the activity of topoisomerase IV, suggesting multitargeting mechanism of action. Compound 8a could form hydrogen bonds and hydrophobic interactions with DNA-topoisomerase IV complex, indicating the insertion of aminothiazolyl moiety was beneficial to improve antibacterial efficiency. These findings indicated that the active carbothioamido hydrazonyl aminothiazolyl quinolone 8a as a chemical therapeutic candidate demonstrated immense potential to tackle drug-resistant bacterial infections.

Unique aminothiazolyl coumarins as potential DNA and membrane disruptors towards Enterococcus faecalis

Aminothiazolyl coumarins as potentially new antimicrobial agents were designed and synthesized in an effort to overcome drug resistance. Biological activity assay revealed that some target compounds exhibited significantly inhibitory efficiencies toward bacteria and fungi including drug-resistant pathogens. Especially, aminothiazolyl 7-propyl coumarin 8b and 4-dichlorobenzyl derivative 11b exhibited bactericidal potential (MBC/MIC = 2) toward clinically drug-resistant Enterococcus faecalis with low cytotoxicity to human lung adenocarcinoma A549 cells, rapidly bactericidal effects and no obvious bacterial resistance development against E. faecalis. The preliminary antibacterial action mechanism studies suggested that compound 11b was able to disturb E. faecalis membrane effectively, and interact with bacterial DNA isolated from resistant E. faecalis through noncovalent bonds to cleave DNA, thus inhibiting the growth of E. faecalis strain. Further molecular modeling indicated that compounds 8b and 11b could bind with SER-1084 and ASP-1083 residues of gyrase-DNA complex through hydrogen bonds and hydrophobic interactions. Moreover, compound 11b showed low hemolysis and in vivo toxicity. These findings of aminothiazolyl coumarins as unique structural scaffolds might hold a large promise for the treatments of drug-resistant bacterial infection.

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.

Current Development of Thiazole-Containing Compounds as Potential Antibacterials against Methicillin-Resistant Staphylococcus aureus

The emergence of multi-drug-resistant bacteria is threatening to human health and life around the world. In particular, methicillin-resistant Staphylococcus aureus (MRSA) causes fatal injuries to human beings and serious economic losses to animal husbandry due to its easy transmission and difficult treatment. Currently, the development of novel, highly effective, and low-toxicity antimicrobials is important to combat MRSA infections. Thiazole-containing compounds with good biological activity are widely used in clinical practice, and appropriate structural modifications make it possible to develop new antimicrobials. Here, we review thiazole-containing compounds and their antibacterial effects against MRSA reported in the past two decades and discuss their structure-activity relationships as well as the corresponding antimicrobial mechanisms. Some thiazole-containing compounds exhibit potent antibacterial efficacy in vitro and in vivo after appropriate structural modifications and could be used as antibacterial candidates. This Review provides insights into the development of thiazole-containing compounds as antimicrobials to combat MRSA infections.

Indole-based aryl sulfides target the cell wall of Staphylococcus aureus without detectable resistance

Sulfur-containing classes of the scaffold "Arylthioindoles" have been evaluated for antibacterial activity; they demonstrated excellent potency against methicillin-resistant Staphylococcus aureus (MRSA) as well as against vancomycin-resistant strains and a panel of clinical isolates of resistant strains. In this study, we have elucidated the mechanism of action of lead compounds, wherein they target the cell wall of S. aureus. Further, S. aureus failed to develop resistance against two lead compounds tested in a serial passage experiment in the presence of the compounds over a period of 40 days. Both the compounds demonstrated comparable in vivo efficacy with vancomycin in a neutropenic mice thigh infection model. The results of these antibacterial activities emphasize the excellent potential of thioethers for developing novel antibiotics and may fill in as a target for the adjustment of accessible molecules to develop new powerful antibacterial agents with fewer side effects.

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.

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.

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.

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.

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.

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.

Design, synthesis, molecular modeling, and antimicrobial potential of novel 3-[(1H-pyrazol-3-yl)imino]indolin-2-one derivatives as DNA gyrase inhibitors

A series of 3-[(1H-pyrazol-3-yl)imino]indolin-2-one derivatives were designed using the molecular hybridization method, characterized using different spectroscopic techniques, and evaluated for their in vitro antimicrobial activity. Most of the target compounds demonstrated good to moderate antimicrobial activity compared with ciprofloxacin and fluconazole. Four compounds (8b, 9a, 9c, and 10a) showed encouraging results, with minimal inhibitory concentration (MIC) values (53.45-258.32 µM) comparable to those of norfloxacin (100.31-200.63 µM) and ciprofloxacin (48.33-96.68 µM). Noticeably, the four derivatives revealed excellent bactericidal and fungicidal activities, except for the bacteriostatic potential of compounds 8b and 9a against Escherichia coli and Staphylococcus aureus, respectively. The time-killing kinetic study against S. aureus confirmed the efficacy of these derivatives. Furthermore, two of the four promising derivatives, 9a and 10a, could prevent the formation of biofilms of S. aureus without affecting the bacterial growth at low concentrations. A combination study with seven commercial antibiotics against the multidrug-resistant bacterium P. aeruginosa showed a notable reduction in the antibiotic MIC values, represented mainly through a synergistic or additive effect. The enzymatic assay implied that the most active derivatives had inhibition potency against DNA gyrase comparable to that of ciprofloxacin. Molecular docking and density functional theory calculations were performed to explore the binding mode and study the reactivity of the promising compounds.

Identification of a novel antifungal backbone of naphthalimide thiazoles with synergistic potential for chemical and dynamic treatment

Aim: The high incidence and prevalence of fungal infections call for new antifungal drugs. This work was to develop naphthalimide thiazoles as potential antifungal agents. Results & methodology: These compounds showed significant antifungal potency toward some tested fungi. Especially, naphthalimide thiazole 4h with excellent anti-Candida tropicalis efficacy possessed good hemolysis level, low toxicity and no obvious resistance. Deciphering the mechanism showed that 4h interacted with DNA and disrupted the antioxidant defense system of C. tropicalis. Compound 4h also triggered membrane depolarization, leakage of cytoplasmic contents and LDH inhibition. Simultaneously, 4h rendered metabolic inactivation and eradicated the formed biofilms of C. tropicalis. Conclusion: The multifaceted synergistic effect initiated by naphthalimide thiazoles is a reasonable treatment window for prospective development.

Potential antibacterial ethanol-bridged purine azole hybrids as dual-targeting inhibitors of MRSA

A new class of antibacterial ethanol-bridged purine azole hybrids as potential dual-targeting inhibitors was developed. Bioactivity evaluation showed that some of the target compounds had prominent antibacterial activity against the tested bacteria, notably, metronidazole hybrid 3a displayed significant inhibitory activity against MRSA (MIC = 6 μM), and had no obvious toxicity on normal mammalian cells (RAW 264.7). In addition, compound 3a also did not induce drug resistance of MRSA obviously, even after fifteen passages. Molecular modeling studies showed that the highly active molecule 3a could insert into the base pairs of topoisomerase IA-DNA as well as topoisomerase IV-DNA through hydrogen bonding. Furthermore, a preliminary study on the antibacterial mechanism revealed that the active molecule 3a could rupture the bacterial membrane of MRSA and insert into MRSA DNA to block its replication, thus possibly exhibiting strong antibacterial activity. These results strongly indicated that the highly active hybrid 3a could be used as a potential dual-targeting inhibitor of MRSA for further development of valuable antimicrobials.

Novel chalcone-conjugated, multi-flexible end-group coumarin thiazole hybrids as potential antibacterial repressors against methicillin-resistant Staphylococcus aureus

The increasing resistance of methicillin-resistant Staphylococcus aureus (MRSA) to antibiotics has led to a growing effort to design and synthesize novel structural candidates of chalcone-conjugated, multi-flexible end-group coumarin thiazole hybrids with outstanding bacteriostatic potential. Bioactivity screening showed that hybrid 5i, which was modified with methoxybenzene, exerted a significant inhibitory activity against MRSA (MIC = 0.004 mM), which was 6 times better than the anti-MRSA activity of the reference drug norfloxacin (MIC = 0.025 mM). Compound 5i neither conferred apparent resistance onto MRSA strains even after multiple passages nor triggered evident toxicity to human hepatocyte LO2 cells and normal mammalian cells (RAW 264.7). Molecular docking showed that highly active molecule 5i might bind to DNA gyrase by forming stable hydrogen bonds. In addition, molecular electrostatic potential surfaces were developed to explain the high antibacterial activity of the target compounds. Furthermore, preliminary mechanism studies suggested that hybrid 5i could disrupt the bacterial membrane of MRSA and insert itself into MRSA DNA to impede its replication, thus possibly becoming a potential antibacterial repressor against MRSA.

Aloe-emodin derived azoles as a new structural type of potential antibacterial agents: design, synthesis, and evaluation of the action on membrane, DNA, and MRSA DNA isomerase

As serious global drug resistance motivated the exploration of new structural drugs, we developed a type of novel structural aloe-emodin azoles as potential antibacterial agents in this work. Some target aloe-emodin azoles displayed effective activity against the tested strains, especially tetrazolyl aloe-emodin 4b showed a low MIC value of 2 μg mL-1 towards MRSA, being more efficient than the reference drug norfloxacin (MIC = 8 μg mL-1). Also, the active molecule 4b exhibited low cytotoxicity against LO2 cells with no distinct tendency to induce the concerned resistance towards MRSA. The tetrazolyl derivative 4b was preliminarily investigated for the possible mechanism; it was revealed that tetrazolyl derivative 4b could both disrupt the integrity of MRSA membrane and form 4b-DNA supramolecular complex by intercalating into DNA. Moreover, tetrazolyl aloe-emodin 4b could bind with MRSA DNA isomerase at multiple sites through hydrogen bonds in molecular simulation.

Membrane active 7-thiazoxime quinolones as novel DNA binding agents to decrease the genes expression and exert potent anti-methicillin-resistant Staphylococcus aureus activity

A novel class of 7-thiazoxime quinolones was developed as potential antimicrobial agents for the sake of bypassing resistance of quinolones. Biological assays revealed that some constructed 7-thiazoxime quinolones possessed effective antibacterial efficiency. Methyl acetate oxime derivative 6l exhibited 32-fold more active than ciprofloxacin against MRSA, which also possessed rapidly bactericidal ability and low toxicity towards mammalian cells. The combination use of 7-thiazoxime quinolone 6l and ciprofloxacin was able to improve antibacterial potency and effectively alleviate bacterial resistance. The preliminarily mechanism exploration revealed that compound 6l could destroy the cell membrane and insert into MRSA DNA to bind with DNA gyrase, then decrease the expression of gyrB and femB genes. The above results strongly suggested that methyl acetate oxime derivative 6l held a promise for combating MRSA infection.

An Overview on Synthetic 2-Aminothiazole-Based Compounds Associated with Four Biological Activities

Amongst sulfur- and nitrogen-containing heterocyclic compounds, the 2-aminothiazole scaffold is one of the characteristic structures in drug development as this essential revelation has several biological activities abiding it to act as an anticancer, antioxidant, antimicrobial and anti-inflammatory agent, among other things. Additionally, various 2-aminothiazole-based derivatives as medical drugs have been broadly used to remedy different kinds of diseases with high therapeutic influence, which has led to their wide innovations. Owing to their wide scale of biological activities, their structural variations have produced attention amongst medicinal chemists. The present review highlights the recently synthesized 2-aminothiazole-containing compounds in the last thirteen years (2008-2020). The originality of this proposal is based on the synthetic strategies developed to access the novel 2-aminothiazole derivatives (N-substituted, 3-substituted, 4-substituted, multi-substituted, aryl/alkyl substituents or acyl/other substituents). The literature reports many synthetic pathways of these 2-aminothiazoles associated with four different biological activities (anticancer, antioxidant, antimicrobial and anti-inflammatory activities). It is wished that this review will be accommodating for new views in the expedition for rationalistic designs of 2-aminothiazole-based medical synthetic pathways.

Novel Schiff base-bridged multi-component sulfonamide imidazole hybrids as potentially highly selective DNA-targeting membrane active repressors against methicillin-resistant Staphylococcus aureus

A new type of Schiff base-bridged multi-component sulfonamide imidazole hybrids with antimicrobial potential was developed. Some target compounds showed significant antibacterial potency. Observably, butylene hybrids 4h exhibited remarkable inhibitory efficacy against clinical MRSA (MIC = 1 µg/mL), but had no significant toxic effect on normal mammalian cells (RAW 264.7). The highly active molecule 4h was revealed by molecular modeling study that it could insert into the base-pairs of DNA hexamer duplex and bind with the ASN-62 residue of human carbonic anhydrase isozyme II through hydrogen bonding. Furthermore, further preliminary antibacterial mechanism experiments confirmed that compound 4h could effectively interfere with MRSA membrane and insert into bacterial DNA isolated from clinical MRSA strains through non-covalent bonding to produce a supramolecular complex, thus exerting its strong antibacterial efficacy by impeding DNA replication. These findings strongly implied that the highly active hybrid 4h could be used as a potential DNA-targeting template for the development of valuable antimicrobial agent.

New Development of Novel Berberine Derivatives against Bacteria

Many berberine derivatives have been synthesized for their antibacterial activity in the past years. In order to elucidate their new Structural Activity Relationship (SAR), the recently synthesized berberine derivatives are reviewed. The newly synthesized berberine derivatives are reported in this review with novel modifications on the berberine structure at various positions. It is hoped that this article would help scientists to design and synthesize new berberine derivatives with high potency and a broad spectrum of antimicrobial activities, more effectiveness and lower toxicity for improved antimicrobial therapy. These berberine derivatives could be developed as novel antibacterial agents to treat patients with infectious diseases, especially caused by resistant bacteria.

An unexpected discovery toward novel membrane active sulfonyl thiazoles as potential MRSA DNA intercalators

Aim: With the increasing emergence of drug-resistant bacteria, the need for new antimicrobial agents has become extremely urgent. This work was to develop sulfonyl thiazoles as potential antibacterial agents. Results & methodology: Novel hybrids of sulfonyl thiazoles were developed from commercial acetanilide and acetylthiazole. Hybrids 6e and 6f displayed excellent inhibitory efficacy against clinical methicillin-resistant Staphylococcus aureus (MRSA) (minimum inhibitory concentration = 1 μg/ml) without obvious toxicity toward normal mammalian cells (RAW 264.7). The combination uses were found to improve the antimicrobial ability. Further preliminary antibacterial mechanism experiments showed that the active molecule 6f could effectively interfere with MRSA membrane and insert into MRSA DNA. Conclusion: Compounds 6e and 6f could serve as potential DNA-targeting templates toward the development of promising antimicrobial agents.

Recent advancements in the medicinal chemistry of bacterial type II topoisomerase inhibitors

Replication proteins are sought as a potential targets for antimicrobial agents. Despite their promising target characteristics, only topoisomerase II inhibitors targeting DNA gyrase and/or topoisomerase IV have reached clinical use. Topoisomerases are the enzymes that are essential for cellular functions and various biological activities. A wide range of natural and synthetic compounds have been identified as potential topoisomerase inhibitors but the resistance is most commonly found in these drugs. The emergence of FQ resistance has increased the need for the development of novel topoisomerase inhibitors with efficacy and high potency against FQ-resistant strains. Besides structural modifications of existing FQ scaffolds, novel non-quinolone topoisomerase II inhibitors, known as novel bacterial topoisomerase inhibitors, have been developed which showed remarkable inhibitory activity against DNA gyrase/topoisomerase IV or both with an improved spectrum of antibacterial potency including drug-resistant strains. This review aims to summarize various recent advancements in the medicinal chemistry of topoisomerase inhibitors with the following objectives: (1) To represent inclusive data on types of topoisomerases and various marketed topoisomerase inhibitors as drugs; (2) To discuss the recent advances in the medicinal chemistry of various topoisomerase inhibitors (DNA gyrase and topo IV) belonging to different structural classes as potential antibacterial agents; (3) To summarizes the structure activity relationship (SAR) including in silico and mechanistic studies to afford ideas and to provide focused direction for the development of new chemical entities which are effective against drug-resistant bacterial pathogens and biofilms.

Balancing Physicochemical Properties of Phenylthiazole Compounds with Antibacterial Potency by Modifying the Lipophilic Side Chain

Bacterial resistance to antibiotics is presently one of the most pressing healthcare challenges and necessitates the discovery of new antibacterials with unique chemical scaffolds. However, the determination of the optimal balance between structural requirements for pharmacological action and pharmacokinetic properties of novel antibacterial compounds is a significant challenge in drug development. The incorporation of lipophilic moieties within a compound's core structure can enhance biological activity but have a deleterious effect on drug-like properties. In this Article, the lipophilicity of alkynylphenylthiazoles, previously identified as novel antibacterial agents, was reduced by introducing cyclic amines to the lipophilic side chain. In this regard, substitution with methylpiperidine (compounds 14-16) and thiomorpholine (compound 19) substituents significantly enhanced the aqueous solubility profile of the new compounds more than 150-fold compared to the first-generation lead compound 1b. Consequently, the pharmacokinetic profile of compound 15 was significantly enhanced with a notable improvement in both half-life and the time the compound's plasma concentration remained above its minimum inhibitory concentration (MIC) against methicillin-resistant Staphylococcus aureus (MRSA). In addition, compounds 14-16 and 19 were found to exert a bactericidal mode of action against MRSA and were not susceptible to resistance formation after 14 serial passages. Moreover, these compounds (at 2× MIC) were superior to the antibiotic vancomycin in the disruption of the mature MRSA biofilm. The modifications to the alkynylphenylthiazoles reported herein successfully improved the pharmacokinetic profile of this new series while maintaining the compounds' biological activity against MRSA.

Thiazole-containing compounds as therapeutic targets for cancer therapy

In the last few decades, considerable progress has been made in anticancer agents development, and several new anticancer agents of natural and synthetic origin have been produced. Among heterocyclic compounds, thiazole, a 5-membered unique heterocyclic motif containing sulphur and nitrogen atoms, serves as an essential core scaffold in several medicinally important compounds. Thiazole nucleus is a fundamental part of some clinically applied anticancer drugs, such as dasatinib, dabrafenib, ixabepilone, patellamide A, and epothilone. Recently, thiazole-containing compounds have been successfully developed as possible inhibitors of several biological targets, including enzyme-linked receptor(s) located on the cell membrane, (i.e., polymerase inhibitors) and the cell cycle (i.e., microtubular inhibitors). Moreover, these compounds have been proven to exhibit high effectiveness, potent anticancer activity, and less toxicity. This review presents current research on thiazoles and elucidates their biological importance in anticancer drug discovery. The findings may aid researchers in the rational design of more potent and bio-target specific anticancer drug molecules.

A new exploration towards aminothiazolquinolone oximes as potentially multi-targeting antibacterial agents: Design, synthesis and evaluation acting on microbes, DNA, HSA and topoisomerase IV

This work did a new exploration towards aminothiazolquinolone oximes as potentially multi-targeting antimicrobial agents. A class of novel hybrids of quinolone, aminothiazole, piperazine and oxime fragments were designed for the first time, conveniently synthesized as well as characterized by ¹H NMR, ¹³C NMR and HRMS spectra. Biological activity showed that some of the synthesized compounds exhibited good antimicrobial activities in comparison with the reference drugs. Especially, O-methyl oxime derivative 10b displayed excellent inhibitory efficacy against MRSA and S. aureus 25923 with MIC values of 0.009 and 0.017 mM, respectively. Further studies indicated that the highly active compound 10b showed low toxicity toward BEAS-2B and A549 cell lines and no obvious propensity to trigger the development of bacterial resistance. Quantum chemical studies have also been conducted and rationally explained the structural features essential for activity. The preliminarily mechanism exploration revealed that compound 10b could not only exert efficient membrane permeability by interfering with the integrity of cells, bind with topoisomerase IV-DNA complex through hydrogen bonds and π-π stacking, but also form a steady biosupramolecular complex by intercalating into DNA to exert the efficient antibacterial activity. The supramolecular interaction between compound 10b and human serum albumin (HSA) was a static quenching, and the binding process was spontaneous, where hydrogen bonds and van der Waals force played vital roles in the supramolecular transportation of the active compound 10b by HSA.

Design and synthesis of aminothiazolyl norfloxacin analogues as potential antimicrobial agents and their biological evaluation

A series of aminothiazolyl norfloxacin analogues as a new type of potential antimicrobial agents were synthesized and screened for their antimicrobial activities. Most of the prepared compounds exhibited excellent inhibitory efficiencies. Especially, norfloxacin analogue II-c displayed superior antimicrobial activities against K. pneumoniae and C. albicans with MIC values of 0.005 and 0.010 mM to reference drugs, respectively. This compound not only showed broad antimicrobial spectrum, rapid bactericidal efficacy and strong enzymes inhibitory potency including DNA gyrase and chitin synthase (CHS), low toxicity against mammalian cells and no obvious propensity to trigger the development of bacterial resistance, but also exerted efficient membrane permeability, and could effectively intercalate into K. pneumoniae DNA to form a steady supramolecular complex, which might block DNA replication to exhibit their powerful antimicrobial activity. Quantum chemical studies were also performed to explain the high antimicrobial activities. Molecular docking showed that compound II-c could bind with gyrase-DNA and topoisomerase IV-DNA through hydrogen bonds and π-π stacking.

Novel potential artificial MRSA DNA intercalators: synthesis and biological evaluation of berberine-derived thiazolidinediones

Novel berberine-derived thiazolidinediones as potential artificial DNA intercalators were synthesized, and the preliminary mechanism suggested that active compound 6b could intercalate into MRSA DNA.

Quinolone derivatives and their activities against methicillin-resistant Staphylococcus aureus (MRSA)

Methicillin-resistant Staphylococcus aureus (MRSA) is the most common pathogen both in hospital and community settings, and is capable of causing serious and even fatal infections. Several antibiotics have been approved for the treatment of infections caused by MRSA, but MRSA has already developed resistance to them. More than ever, it's imperative to develop novel, high effective and fast acting anti-MRSA agents. Quinolones are one of the most common antibiotics in clinical practice used to treat various bacterial infections, and some of them displayed excellent in vitro and in vivo anti-MRSA activities, so quinolone derivatives are one of the most promising candidates. This review summarizes the recent developments of quinolone derivatives with potential activity against MRSA, and the structure-activity relationship is also discussed.

Novel organophosphorus aminopyrimidines as unique structural DNA-targeting membrane active inhibitors towards drug-resistant methicillin-resistant Staphylococcus aureus

A series of novel unique structural organophosphorus aminopyrimidines were developed as potential DNA-targeting membrane active inhibitors through an efficient one-pot procedure from aldehydes, phosphonate and aminopyrimidine. The biological assay revealed that some of the prepared compounds displayed antibacterial activities. In particular, imidazole derivative 2c exhibited more potent inhibitory activity against MRSA with an MIC value of 4 μg mL^-1 in comparison with the clinical drugs chloromycin and norfloxacin. Experiments revealed that the active molecule 2c had the ability to rapidly kill the tested strains without obviously triggering the development of bacterial resistance, showed low toxicity to L929 cells and could disturb the cell membrane. The molecular docking study discovered that compound 2c could bind with DNA gyrase via hydrogen bonds and other weak interactions. Further exploration disclosed that the active molecule 2c could also effectively intercalate into MRSA DNA and form a steady 2c-DNA supramolecular complex, which might further block DNA replication to exert powerful antibacterial effects.

Discovery of Benzimidazole-Quinolone Hybrids as New Cleaving Agents toward Drug-Resistant Pseudomonas aeruginosa DNA

A series of benzimidazole-quinolone hybrids as new potential antimicrobial agents were designed and synthesized. Bioactive assays indicated that some of the prepared compounds exhibited potent antibacterial and antifungal activities. Notably, 2-fluorobenzyl derivative 5 b (ethyl 7-chloro-6-fluoro-1-[[1-[(2-fluorophenyl)methyl]benzimidazol-2-yl]methyl]-4-oxo-quinoline-3-carboxylate) showed remarkable antimicrobial activity against resistant Pseudomonas aeruginosa and Candida tropicalis isolated from infected patients. Active molecule 5 b could not only rapidly kill the tested strains, but also exhibit low toxicity toward Hep-2 cells. It was more difficult to trigger the development of bacterial resistance of P. aeruginosa against 5 b than that against norfloxacin. Molecular docking demonstrated that 5 b could effectively bind with topoisomerase IV-DNA complexes, and quantum chemical studies theoretically elucidated the good antimicrobial activity of compound 5 b. Preliminary experimental reaction mechanism exploration suggested that derivative 5 b could not intercalate into DNA isolated from drug-resistant P. aeruginosa, but was able to cleave DNA effectively, which might further block DNA replication to exert powerful bioactivities. In addition, compound 5 b is a promising antibacterial agent with membrane disruption abilities.

Novel naphthalimide nitroimidazoles as multitargeting antibacterial agents against resistant Acinetobacter baumannii

Aim: The increasing emergence of resistant bacteria imposed an urgent request to discover novel antibacterial agents. This work was to develop naphthalimide nitroimidazoles as potentially antibacterial agents. Results/methodology: Compound 9e showed the strong antibacterial activity (minimal inhibitory concentration = 0.013 μmol/ml) against resistant Acinetobacter baumannii (A. baumannii) with rapid killing effect and no obvious triggering of the development of resistance. Its combination use with chloromycin, norfloxacin or clinafloxacin improved the antibacterial potency. It could not only effectively permeate membrane of resistant A. baumannii bacteria, but also intercalate into resistant A. baumannii DNA to form 9e–DNA complex. The interaction with bacterial DNA gyrase B was driven by hydrogen bonds. Conclusion: Compound 9e should be a potentially multitargeting antibacterial agent against resistant A. baumannii.

Discovery of a Novel Dibromoquinoline Compound Exhibiting Potent Antifungal and Antivirulence Activity That Targets Metal Ion Homeostasis

Globally, invasive fungal infections pose a significant challenge to modern human medicine due to the limited number of antifungal drugs and the rise in resistance to current antifungal agents. A vast majority of invasive fungal infections are caused by species of Candida, Cryptococcus, and Aspergillus. Novel antifungal molecules consisting of unexploited chemical scaffolds with a unique mechanism are a pressing need. The present study identifies a dibromoquinoline compound (4b) with broad-spectrum antifungal activity that inhibits the growth of pertinent species of Candida (chiefly C. albicans), Cryptococcus, and Aspergillus at a concentration of as low as 0.5 μg/mL. Furthermore, 4b, at a subinhibitory concentration, interfered with the expression of two key virulence factors (hyphae and biofilm formation) involved in C. albicans pathogenesis. Three yeast deletion strains ( cox17Δ, ssa1Δ, and aft2Δ) related to metal ion homeostasis were found to be highly sensitive to 4b in growth assays, indicating that the compound exerts its antifungal effect through a unique, previously unexploited mechanism. Supplementing the media with either copper or iron ions reversed the strain sensitivity to 4b, further corroborating that the compound targets metal ion homeostasis. 4b's potent antifungal activity was validated in vivo, as the compound enhanced the survival of Caenorhabditis elegans infected with fluconazole-resistant C. albicans. The present study indicates that 4b warrants further investigation as a novel antifungal agent.

Potential Antimicrobial Isopropanol-Conjugated Carbazole Azoles as Dual Targeting Inhibitors of Enterococcus faecalis

A series of isopropanol-bridged carbazole azoles as potential antimicrobial agents were designed and synthesized from commercial carbazoles. Bioassay revealed that 3,6-dichlorocarbazolyl triazole 3f could effectively inhibit the growth of E. faecalis with minimal inhibitory concentration of 2 μg/mL. The active molecule 3f showed lower propensity to trigger the development of resistance in bacteria than norfloxacin and exerted rapidly bactericidal ability. Compound 3f also exhibited low cytotoxicity to normal mammalian RAW264.7 cells. Further mechanism exploration indicated that conjugate 3f was membrane active against E. faecalis and could form 3f-DNA complex by intercalating into DNA of resistant E. faecalis, which might be responsible for its antimicrobial action. Molecular docking showed an efficient binding of triazole derivative 3f with DNA gyrase enzyme through noncovalent interactions.