Novel benzimidazolyl tetrahydroprotoberberines: Design, synthesis, antimicrobial evaluation and multi-targeting exploration

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.

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.

Benzimidazole analogues as efficient arsenals in war against methicillin-resistance staphylococcus aureus (MRSA) and its SAR studies

Small molecule based inhibitors development is a growing field in medicinal chemistry. In recent years, different heterocyclic derivatives have been designed to counter the infections caused by multi-drug resistant bacteria. Indeed, small molecule inhibitors can be employed as an efficient antibacterial agents with different mechanism of action. Methicillin-resistant Staphylococcus aureus (MRSA) is becoming lethal to mankind due to easy transmission mode, rapid resistance development to existing antibiotics and affect difficult-to-treat skin and filmsy diseases. Benzimidazoles are a class of heterocyclic compounds which have capability to fight against MRSA. High biocompatibility of benzimidazoles, synergistic behaviour with antibiotics and their tunable physico-chemical properties attracted the researchers to develop new benzimidazole based antibacterial agents. The present review focus on recent developments of benzimidazole-hybrid molecules as anti MRSA agents and the results of in-vitro and in-vivo studies with possible mechanism of action and discussing structure-activity relationship (SAR) in different directions. Benzimdazoles act as DNA binding agents, enzyme inhibitors, anti-biofilm agents and showed synergistic effect with available antibiotics to achieve antibacterial activity against MRSA. This cumulative figures would help to design new benzimidazole-based MRSA growth inhibitors.

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.

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.

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.

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.

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.

Novel potentially antifungal hybrids of 5-flucytosine and fluconazole: Design, synthesis and bioactive evaluation

A series of novel potentially antifungal hybrids of 5-flucytosine and fluconazole were designed, synthesized and characterized by ¹H NMR, ¹³C NMR, IR and HRMS spectra. Bioactive assay manifested that some prepared compounds showed moderate to good antifungal activities in comparison with fluconazole and 5-flucytosine. Remarkably, the 3,4-dichlorobenzyl hybrid 7h could inhibit the growth of C. albicans ATCC 90023 and clinical resistant strain C. albicans with MIC values of 0.008 and 0.02 mM, respectively. The active molecule 7h could not only rapidly kill C. albicans but also efficiently permeate membrane of C. albicans. Molecular docking study revealed that compound 7h could interact with the active site of CACYP51 through hydrogen bond. Quantum chemical studies were also performed to explain the high antifungal activity. Further preliminary mechanism research suggested that molecule 7h could intercalate into calf thymus DNA to form a steady supramolecular complex, which might block DNA replication to exert the powerful bioactivities.