Investigating the Antibacterial Activity of Biphenylthiazoles against Methicillin- and Vancomycin-Resistant Staphylococcus aureus (MRSA and VRSA)

Design, Synthesis, Biological Evaluation, and Molecular Docking Studies of Pleuromutilin Derivatives Containing Thiazole

In this study, we designed and synthesized a series of pleuromutilin derivatives containing thiazole. The in vitro antimicrobial efficacy of these synthesized compounds was examined by using four strains. Compared with tiamulin (MIC = 0.25 μg/mL), compound 14 exhibited potency in inhibiting MRSA growth (MIC = 0.0625 μg/mL) in these derivatives. Meanwhile, the time-killing kinetics further demonstrated that compound 14 could efficiently inhibit the MRSA growth. After exposure at 4 × MIC, the postantibiotic effect (PAE) of compound 14 was 1.29 h. Additionally, in thigh-infected mice, compound 14 exhibited a more potent antibacterial efficacy (-1.78 ± 0.28 log10 CFU/g) in reducing MRSA load compared to tiamulin (-1.21 ± 0.23 log10 CFU/g). Moreover, the MTT assay on RAW 264.7 cells demonstrated that compound 14 (8 μg/mL) had no significant cytotoxicity. Docking studies indicated the strong affinity of compound 14 toward the 50S ribosomal subunit, with a binding free energy of -9.63 kcal/mol. Taken together, it could be deduced that compound 14 was a promising candidate for treating MRSA infections.

Synthesis and structure-activity relationship of novel thiazole aminoguanidines against MRSA and Escherichia coli

Novel lead thiazole aminoguanidines exhibited strong activity against Gram-positive bacteria. The potential targets of these substances are undecaprenyl diphosphate synthase (UPPS) and undecaprenyl diphosphate phosphatase (UPPP). Here, we report the synthesis and antibacterial evaluation of a library of thiazole aminoguanidines analogues, wherein the rotatable bond is inserted between the C2 position of thiazole and hydrophobic group. The molecular flexibility is increased, and new analogues with strong activity against MRSA and E. coli are produced. The best compound 4i showed rapid sterilization and low tendency to induce bacterial resistance. The IC50 of compound 4i to EcUPPS enzyme is 145 μmol L-1 (58 μg mL-1). Compound 4i can also inhibit and destroy bacterial biofilms. These thiazole aminoguanidines can be developed as potential therapeutic candidates in the future.

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.

Discovery of Unique Bis-Substituted Aromatic Amide Derivatives as Novel Highly Potent Antibiotics for Combating Methicillin-Resistant Staphylococcus aureus (MRSA)

Due to the increasing antibiotic resistance, developing novel antimicrobials to fight infections caused by resistant bacteria is imperative. Herein, a series of novel bis-substituted aromatic amides were designed and synthesized through modifying the hit compound 1, and their antimicrobial activities were evaluated. Among them, compound 4t, as the most potent lead, exhibited excellent antimicrobial activities against Gram-positive bacteria, including clinical methicillin-resistant Staphylococcus aureus (MRSA) isolates, while keeping weak hemolytic and mammalian cytotoxic activities. Furthermore, compound 4t displayed rapid bactericidal capabilities, low tendency to produce resistance, and favorable capacities to destroy bacterial biofilms. Further explorations indicated that compound 4t induces bacterial death by binding to cardiolipin (CL) on the bacterial membrane, disrupting the cell membrane, and facilitating the accumulation of reactive oxygen species (ROS). Additionally, compound 4t showed remarkable anti-MRSA activity in vivo, demonstrating compound 4t could be developed as a potential candidate to combat MRSA infections.

Design and synthesis of etrasimod derivatives as potent antibacterial agents against Gram-positive bacteria

The emergence of multidrug-resistant bacteria along with a declining pipeline of clinically useful antibiotics has led to the urgent need for the development of more effective antibacterial agents. Inspired by our recent report on the antibacterial activity of etrasimod, an immunomodulating drug candidate, we prepared a series of etrasimod derivatives by varying substituents on the phenyl ring, altering the central tricyclic aromatic ring, and modifying the carboxyl group. From this series of compounds, indole derivative 24f was identified as the most potent antibacterial compound, with the minimum inhibitory concentration (MIC) values between 2.5 and 10 μM against various Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), S. epidermidis and enterococci. Moreover, 24f exhibited rapid bactericidal activity against S. aureus, low toxicity and hemolytic activity, and a synergistic effect with gentamicin against S. aureus, MRSA, and Enterococcus faecalis. Furthermore, it was shown that neither etrasimod nor 24f affects S. aureus cell membranes. Importantly, 24f did not induce resistance in S. aureus, representing a significant improvement compared to etrasimod. Finally, the antibacterial activity of etrasimod and 24f against S. aureus and MRSA was confirmed in vivo in a Caenorhabditis elegans infection model. Taken together, our study highlights the value of etrasimod and its derivatives as potential antibacterial candidates for combating infections caused by Gram-positive bacteria.

Naphthylthiazoles: a class of broad-spectrum antifungals

Cryptococcal infections remain a major cause of mortality worldwide due to the ability of Cryptococci to pass through the blood-brain barrier (BBB) causing lethal meningitis. The limited number of available therapeutics, which exhibit limited availability, severe toxicity and low tolerability, necessitates the development of new therapeutics. Investigating the antifungal activity of a novel series of naphthylthiazoles provided trans-diaminocyclohexyl derivative 18 with many advantageous attributes as a potential therapeutic for cryptococcal meningitis. Briefly, the antimycotic activity of 18 against cryptococcal strains was highly comparable to that of amphotericin-B and fluconazole with MIC values as low as 1 μg mL-1. Moreover, compound 18 possessed additional advantages over fluconazole; it significantly reduced the intracellular burden of Cryptococci and markedly inhibited cryptococcal biofilm formation. Initial PK assessment of 18 indicated its ability to reach the CNS after oral administration with high permeability, and it maintained therapeutic plasma concentrations for 18 h. Its antifungal activity extended to other clinically relevant strains, such as fluconazole-resistant C. auris.

Expanding the structure-activity relationships of alkynyl diphenylurea scaffold as promising antibacterial agents

With the continuous and alarming threat of exhausting the current antimicrobial arsenals, efforts are urgently needed to develop new effective ones. In this study, the antibacterial efficacy of a set of structurally related acetylenic-diphenylurea derivatives carrying the aminoguanidine moiety was tested against a panel of multidrug-resistant Gram-positive clinical isolates. Compound 18 was identified with a superior bacteriological profile than the lead compound I. Compound 18 demonstrated an excellent antibacterial profile in vitro: low MIC values, extended post-antibiotic effect, refractory ability to resistance development upon extended repeated exposure, and high tolerability towards mammalian cells. Finally, when assessed in a MRSA skin infection animal model, compound 18 showed considerable healing and less inflammation, decrease in the bacterial loads in skin lesions, and it surpassed fusidic acid in controlling the systemic dissemination of S. aureus. Collectively, compound 18 represents a promising lead anti-MRSA agent that merits further investigation for the development of new anti-staphylococcal therapeutics.

The Anti-MRSA Activity of Phenylthiazoles: A Comprehensive Review

Antimicrobial resistance is an aggravating global issue therefore it has been under extensive research in an attempt to reduce the number of antibiotics that are constantly reported as obsolete jeopardizing the lives of millions worldwide. Thiazoles possess a reputation as one of the most diverse biologically active nuclei, and phenylthiazoles are no less exceptional with an assorted array of biological activities such as anthelmintic, insecticidal, antimicrobial, antibacterial, and antifungal activity. Recently phenyl thiazoles came under the spotlight as a scaffold having strong potential as an anti-MRSA lead compound. It is a prominent pharmacophore in designing and synthesizing new compounds with antibacterial activity against multidrug-resistant bacteria such as MRSA, which is categorized as a serious threat pathogen, that exhibited concomitant resistance to most of the first-line antibiotics. MRSA has been associated with soft tissue and skin infections resulting in high death rates, rapid dissemination, and loss of millions of dollars of additional health care costs. In this brief review, we have focused on the advances of phenylthiazole derivatives as potential anti-MRSA from 2014 to 2021. The review encompasses the effect on biological activity due to combining this molecule with various synthetic pharmacophores. The physicochemical aspects were correlated with the pharmacokinetic properties of the reviewed compounds to reach a structure-activity relationship profile. Lead optimization of phenyl thiazole derivatives has additionally been outlined where the lipophilicity of the compounds was balanced with the metabolic stability and oral solubility to aid the researchers in medicinal chemistry, design, and synthesizing effective anti- MRSA phenylthiazoles in the future.

The Inhibitory Efficiencies of Geraniol as an Anti-Inflammatory, Antioxidant, and Antibacterial, Natural Agent Against Methicillin-Resistant Staphylococcus aureus Infection in vivo

Introduction

Antibiotics wee widely used as feed additives in animal husbandry. With the increase of drug resistance of bacteria, there is an urgent need to find alternatives to antibiotics. Clinically, methicillin-resistant Staphylococcus aureus (MRSA) infections account for about 25% to 50% of Staphylococcus aureus infections worldwide. Similarly, it is also one of the pathogens that cause serious animal infections.

Methods

We established a mouse model of systemic infection of MRSA to study the preventive effect of geraniol on MRSA and the immunomodulatory effect of geraniol. The mice in the experiment were injected with geraniol by intramuscular injection and were fed intraperitoneally with minimum lethal dose of MRSA. Then, the survival rate, inflammatory cytokines, oxidative stress factors in serum were measured. These values were used to estimate the bacterial load in different organs and to assess histopathological changes in the lungs, liver and kidneys.

Results

The above-mentioned two ways of using geraniol could prevent MRSA infection in vivo in mice and showed a significant dose–response relationship. In other words, geraniol significantly decreased the concentrations of inflammatory cytokines and oxidative stress factors in MRSA-infected mice. At the same time, the level of glutathione peroxidase also increased in a dose–proportional relationship. In the group of mice treated with geraniol, their superoxide dismutase levels were significantly higher than those in the vancomycin. After treatment with geraniol, the burden of MRSA decreased. No obvious histopathological abnormalities were found in the liver and kidney of MRSA-infected mice. In addition, geraniol improved the inflammatory changes in the lungs.

Conclusion

The results indicated that geraniol was a natural substance that could be used as an anti-inflammatory, antioxidant and antibacterial substance to protect mice from MRSA systemic infection. Generally, the research shows that as a natural medicine, geraniol has broad potential in the development and application of antibiotic substitutes.

Thiazole Ring-A Biologically Active Scaffold

BACKGROUND

Thiazole is a good pharmacophore nucleus due to its various pharmaceutical applications. Its derivatives have a wide range of biological activities such as antioxidant, analgesic, and antimicrobial including antibacterial, antifungal, antimalarial, anticancer, antiallergic, antihypertensive, anti-inflammatory, and antipsychotic. Indeed, the thiazole scaffold is contained in more than 18 FDA-approved drugs as well as in numerous experimental drugs.

OBJECTIVE

To summarize recent literature on the biological activities of thiazole ring-containing compounds Methods: A literature survey regarding the topics from the year 2015 up to now was carried out. Older publications were not included, since they were previously analyzed in available peer reviews.

RESULTS

Nearly 124 research articles were found, critically analyzed, and arranged regarding the synthesis and biological activities of thiazoles derivatives in the last 5 years.

Design, synthesis and bioactivity evaluation of novel pyrazole linked phenylthiazole derivatives in context of antibacterial activity

Methicillin-resistant Staphylococcus aureus (MRSA) infections are a significant burden both clinically and economically worldwide. Increasing resistance to current antibiotics requires an urgent investigation into novel classes of antimicrobial agents. This study presents a structure-activity relationship (SAR) rationale for pyrazole linked phenylthiazole analogues as new antibacterial agents. A library of 23 novel pyrazole linked phenylthiazole compounds were synthesised, followed by screening for antimicrobial activity against five bacterial species and two fungi. The most active compound 14b has shown promising antibacterial activity against the Gram-positive methicillin-resistant Staphylococcus aureus (MRSA, ATCC 43300) strain (MIC 4 μg/mL). Furthermore, the active pyrazole linked phenylthiazole compound exhibited a better toxicity profile than standard antibiotics. In summary, these results demonstrate that a pyrazole linked phenylthiazole scaffold has potential as a lead for further investigation to afford novel antibacterial agents.

A key review on oxadiazole analogs as potential methicillin-resistant Staphylococcus aureus (MRSA) activity: Structure-activity relationship studies

Methicillin-resistant Staphylococcus aureus (MRSA) is becoming dangerous to human beings due to easy transmission mode and leading to the difficult-to-treat situation. The rapid resistance development of MRSA to many approved antibiotics is of major concern. There is a lot of scope to develop novel, efficient, specific, and nontoxic drug candidates to fight against MRSA isolates. The interesting molecular structure and adaptable feature of oxadiazole moiety which are bioisosteres of esters and amides, and these functional groups show improved resistance to esterases mediated hydrolytic cleavage, attracting researchers to develop required novel antibiotics based on oxadiazole core. This review summarizes the developments of oxadiazole-containing derivatives as potent antibacterial agents against multidrug-resistant MRSA strains and discussing the structure-activity relationship (SAR) in various directions. The current survey is the highlight of the present scenario of oxadiazole hybrids on MRSA studies, covering articles published from 2011 to 2020. This collective information may become a good platform to plan and develop new oxadiazole-based small molecule growth inhibitors of MRSA with minimal side effects.

4-4-(Anilinomethyl)-3-[4-(trifluoromethyl)phenyl]-1H-pyrazol-1-ylbenzoic acid derivatives as potent anti-gram-positive bacterial agents

A collection of potent antimicrobials consisting of novel 1,3-bis-benzoic acid and trifluoromethyl phenyl derived pyrazoles has been synthesized and tested for antibacterial activity. The majority of trifluoromethyl phenyl derivatives are highly potent growth inhibitors of Gram-positive bacteria and showed low toxicity to human cultured cells. In particular, two compounds (59 and 74) were selected for additional studies. These compounds are highly effective against Staphylococcus aureus as shown by a low minimum inhibitory concentration (MIC), a bactericidal effect in time-kill assays, moderate inhibition of biofilm formation as well as biofilm destruction, and a bactericidal effect against stationary phase cells representing non-growing persister cells. Multistep resistance assays showed a very low tendency for S. aureus and Enterococcus faecalis to develop resistance through mutation. Additionally, in vivo mouse model studies showed no harmful effects at doses up to 50 mg/kg using 14 blood plasma organ toxicity markers or TUNEL assay in liver and kidney. Investigations into the mode of action by performing macromolecular synthesis inhibition studies showed a broad range of inhibitory effects, suggesting targets that have a global effect on bacterial cell function.

Development of Biphenylthiazoles Exhibiting Improved Pharmacokinetics and Potent Activity Against Intracellular Staphylococcus aureus

Exploring the structure-activity relationship (SAR) at the cationic part of arylthiazole antibiotics revealed hydrazine as an active moiety. The main objective of the study is to overcome the inherited toxicity associated with the free hydrazine. A series of hydrocarbon bridges was inserted in between the groups, to separate the two amino groups. Hence, the aminomethylpiperidine-containing analog 16 was identified as a new promising antibacterial agent with efficient antibacterial and pharmacokinetic profiles. Briefly, compound 16 outperformed vancomycin in terms of the antibacterial spectrum against vancomycin-resistant staphylococcal and enterococcal strains with minimum inhibitory concentrations (MICs) ranging from 2 to 4 μg/mL, which is a faster bactericidal mode of action, completely eradicating the high staphylococcal burden within 6-8 h, and it has a unique ability to completely clear intracellular staphylococci. In addition, the initial pharmacokinetic assessment confirmed the high metabolic stability of compound 16 (biological half-life >4 h); it had a good extravascular distribution and maintained a plasma concentration higher than the average MIC value for over 12 h. Moreover, compound 16 significantly reduced MRSA burden in an in vivo MRSA skin infection mouse experiment. These attributes collectively suggest that compound 16 is a good therapeutic candidate for invasive staphylococcal and enterococcal infections. From a mechanistic point of view, compound 16 inhibited undecaprenyl diphosphate phosphatase (UppP) with an IC₅₀ value of 29 μM.

Development of coinage metal nanoclusters as antimicrobials to combat bacterial infections

Infections from antibiotic-resistant bacteria have caused huge economic loss and numerous deaths over the past decades. Researchers are exploring multiple strategies to combat these bacterial infections. Metal nanomaterials have been explored as therapeutics against these infections owing to their relatively low toxicity, broad-spectrum activity, and low bacterial resistance development. Some coinage metal nanoclusters, such as gold, silver, and copper nanoclusters, can be readily synthesized. These nanoclusters can feature multiple useful properties, including ultra-small size, high catalytic activity, unique photoluminescent properties, and photothermal effect. Coinage metal nanoclusters have been investigated as antimicrobials, but more research is required to tap their full potential. In this review, we discuss multiple advantages and the prospect of using gold/silver/copper nanoclusters as antimicrobials.

Discovery, Synthesis, and Biological Evaluation of Dunnianol-Based Mannich Bases against Methicillin-Resistant Staphylococcus aureus (MRSA)

Dunnianol, a natural sesqui-neoligan derived from the leaves and stems of Illicium simonsii Maxim, has been found to possess moderate antibacterial activity. To improve the antibacterial activity and solubility of dunnianol, a series of dunnianol-based Mannich bases were prepared and evaluated for their antibacterial activities. The most promising compound, 5a', exhibited excellent antibacterial activity against Staphylococcus aureus and clinically isolated methicillin-resistant Staphylococcus aureus (MRSA) with MIC values of 1 to 2 μg/mL. Structure-activity relationships indicated that the introduction of (dimethylamino)methyl at the ortho position of the phenolic hydroxyl group of dunnianol could obtain a more active compound. A mechanism study revealed that 5a' killed MRSA more rapidly than did vancomycin by disrupting the cell membrane. Moreover, 5a' was not susceptible to drug resistance development and also showed low toxicity and good antibacterial efficacy in vivo. These results indicate that the dunnianol-based Mannich base 5a' could be a promising antibiotic candidate for further research.

Pentamidine sensitizes FDA-approved non-antibiotics for the inhibition of multidrug-resistant Gram-negative pathogens

Pentamidine sensitizes FDA-approved antibiotics to combat Gram-negative pathogens. We screened 1374 FDA-approved non-antibiotics for their ability to be sensitized by pentamidine against Escherichia coli. We identified mitomycin C and mefloquine as potent hits effective against multiple drug-resistant, Gram-negative bacteria. Killing kinetics and an in vivo model with Caenorhabditis elegans (C. elegans) revealed that such combinations produced synergy against colistin-resistant Enterobacter cloacae (E. cloacae). These findings suggest combinations of FDA-approved non-antibiotics, and pentamidine can be repurposed into new antimicrobial agents.

Oxadiazolylthiazoles as novel and selective antifungal agents

Studying the structure-activity relationships (SAR) of oxadiazolylthiazole antibiotics unexpectedly led us to identify ethylenediamine- and propylenediamine-analogs as potential antimycotic novel lead structures. Replacement of the ethylenediamine moiety for the lead compound 7 with cis-diaminocyclohexyl group (compound 18) significantly enhanced the antifungal activity. In addition to the high safety margin of 18 against mammalian cells, it showed highly selective broad-spectrum activity against fungal cells without inhibiting the human normal microbiota. The antifungal activity of 18 was investigated against 20 drug-resistant clinically important fungi, including Candida species, Cryptococcus, and Aspergillus fumigatus strains. In addition to the low MIC values that mostly ranged between 0.125 and 2.0 μg/mL, compound 18 outperformed fluconazole in disrupting mature Candida biofilm.

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.

Identification of a Phenylthiazole Small Molecule with Dual Antifungal and Antibiofilm Activity Against Candida albicans and Candida auris

Candida species are a leading source of healthcare infections globally. The limited number of antifungal drugs combined with the isolation of Candida species, namely C. albicans and C. auris, exhibiting resistance to current antifungals necessitates the development of new therapeutics. The present study tested 85 synthetic phenylthiazole small molecules for antifungal activity against drug-resistant C. albicans. Compound 1 emerged as the most potent molecule, inhibiting growth of C. albicans and C. auris strains at concentrations ranging from 0.25–2 µg/mL. Additionally, compound 1 inhibited growth of other clinically-relevant yeast (Cryptococcus) and molds (Aspergillus) at a concentration as low as 0.50 µg/mL. Compound 1 exhibited rapid fungicidal activity, reducing the burden of C. albicans and C. auris below the limit of detection within 30 minutes. Compound 1 exhibited potent antibiofilm activity, similar to amphotericin B, reducing the metabolic activity of adherent C. albicans and C. auris biofilms by more than 66% and 50%, respectively. Furthermore, compound 1 prolonged survival of Caenorhabditis elegans infected with strains of C. albicans and C. auris, relative to the untreated control. The present study highlights phenylthiazole small molecules, such as compound 1, warrant further investigation as novel antifungal agents for drug-resistant Candida infections.

Modifying the lipophilic part of phenylthiazole antibiotics to control their drug-likeness

Compounds with high lipophilic properties are often associated with bad physicochemical properties, triggering many off-targets, and less likely to pass clinical trials. Two metabolically stable phenylthiazole antibiotic scaffolds having notable high lipophilic characters, one with alkoxy side chain and the other one with alkynyl moiety, were derivatized by inserting a cyclic amine at the lipophilic tail with the objective of improving physicochemical properties and the overall pharmacokinetic behavior. Only alkynyl derivatives with 4- or 5-membered rings showed remarkable antibacterial activity. The azetidine-containing compound 8 was the most effective and it revealed a potent antibacterial effect against 15 multi-drug resistant (MDR)-Gram positive pathogens including Staphylococcus aureus, Streptococcus pneumoniae, Staphylococcus epidermidis and enterococci. Compound 8 was also highly effective in clearing 99.7% of the intracellular methicillin-resistant S. aureus (MRSA) harbored inside macrophages. In addition to the remarkable enhancement in aqueous solubility, the in vivo pharmacokinetic study in rats indicated that compound 8 can penetrate gut cells and reach plasma at a therapeutic concentration within 15 min and maintain effective plasma concentration for around 12 h. Interestingly, the main potential metabolite (compound 9) was also active as an antibacterial agent with potent antibiofilm activity.

Synthesis and antibacterial evaluation of a novel library of 2-(thiazol-5-yl)-1,3,4-oxadiazole derivatives against methicillin-resistant Staphylococcus aureus (MRSA)

Replacement of the n-butylphenyl moiety in the lipophilic part of the previously reported arylthiazole antibiotics with naphthyl ring amended its activity against vancomycin resistant strains of Staphylococcus aureus. Incorporation of the CN linker connecting the nitrogenous head with thiazole within an oxadiazole ring provided orally available analogs with relatively long half-life. In this article, a set of new twenty-three derivatives of 2-(thiazol-5-yl)-1,3,4-oxadiazole was synthesized combining both structural modifications in one new scaffold with the objectives of enhancing both the pharmacokinetic profile and antibacterial activities vs. malicious microbes. Among the synthesized new compounds, five derivatives showed promising activity with MIC values ranging from 1.95 to 3.90 μg/mL. The guanidinyl-containing naphthylthiazole and N-methylpiperazinyl derivatives (25 &29) were found equipotent as vancomycin against MRSA (2658 RCMB). The other three derivatives (23, 24 and 26) revealed 50% of vancomycin activity.

Nanoparticles from Actinobacteria: A Potential Target to Antimicrobial Therapy

Nanoparticles have gained significant importance in the past two decades, due to their multifaceted applications in the field of nanomedicine. As our ecosystems and habitats are changing due to global warming, many new diseases are emerging continuously. Treating these costs a lot of money and mostly ends up in failure. In addition, frequent use of antibiotics to control the emerging diseases has led the pathogens to develop resistance to antibiotics. Hence, the nanoparticles are targeted to treat such diseases instead of the costly antibiotics. In particular, the biosynthesized nanoparticles have received considerable attention due to their simple, eco-friendly and promising activity. To highlight, microbial mediated nanoparticles have been found to possess higher activity and thus have a promising role in antimicrobial therapy to fight against the emerging drug-resistant pathogens. In this context, this review article is aimed at highlight the role of nanoparticles in the field of nanomedicine and importance of actinobacteria in the nanoparticle synthesis and their need in antimicrobial therapy. This is a comprehensive review, focusing on the potential of actinobacteria-mediated nanoparticles in the field of nanomedicine.

Promising antibacterial agents against multidrug resistant Staphylococcus aureus

Rapid emergence of multidrug resistant Staphylococcus aureus infections has created a critical health menace universally. Resistance to all the available chemotherapeutics has been on rise which led to WHO to stratify Staphylococcus aureus as high tier priorty II pathogen. Hence, discovery and development of new antibacterial agents with new mode of action is crucial to address the multidrug resistant Staphylococcus aureus infections. The egressing understanding of new antibacterials on their biological target provides opportunities for new therapeutic agents. This review underlines on various aspects of drug design, structure activity relationships (SARs) and mechanism of action of various new antibacterial agents and also covers the recent reports on new antibacterial agents with potent activity against multidrug resistant Staphylococcus aureus. This review provides attention on in vitro and in vivo pharmacological activities of new antibacterial agents in the point of view of drug discovery and development.

Peptidoglycan pathways: there are still more!

The discovery of 3rd and 4th generations of currently existing classes of antibiotics has not hindered bacterial resistance, which is escalating at an alarming global level. This review follows WHO recommendations through implementing new criteria for newly discovered antibiotics. These recommendations focus on abandoning old scaffolds and hitting new targets. In light of these recommendations, this review discusses seven bacterial proteins that no commercial antibiotics have targeted yet, alongside their reported chemical scaffolds.

Phenylthiazoles with nitrogenous side chain: An approach to overcome molecular obesity

A novel series of phenylthiazoles bearing cyclic amines at the phenyl-4 position was prepared with the objective of decreasing lipophilicity and improving the overall physicochemical properties and pharmacokinetic profile of the compounds. Briefly, the piperidine ring (compounds 10 and 12) provided the best ring size in terms of antibacterial activity when tested against 16 multidrug-resistant clinical isolates. Both compounds were superior to vancomycin in the ability to eliminate methicillin-resistant Staphylococcus aureus (MRSA), residing within infected macrophages and to disrupt mature MRSA biofilm. Additionally, compounds 10 and 12 exhibited a fast-bactericidal mode of action in vitro. Furthermore, the new derivatives were 160-times more soluble in water than the previous lead compound 1b. Consequently, compound 10 was orally bioavailable with a highly-acceptable pharmacokinetic profile in vivo that exhibited a half-life of 4 h and achieved a maximum plasma concentration that exceeded the minimum inhibitory concentration (MIC) values against all tested bacterial isolates.

An aryl isonitrile compound with an improved physicochemical profile that is effective in two mouse models of multidrug-resistant Staphylococcus aureus infection

OBJECTIVES

The aim of this study was to investigate the antibacterial activity of a synthetic aryl isonitrile compound (35) that was developed as part of a compound library to identify new antibacterial agents effective against methicillin-resistant Staphylococcus aureus (MRSA).

METHODS

Compound 35 was evaluated against MRSA isolates by the broth microdilution assay and for toxicity to mammalian keratinocytes using the MTS assay. A multistep resistance selection assay was conducted to investigate MRSA resistance development to 35. A Caco-2 bidirectional permeability assay was employed to evaluate the ability of 35 to permeate across the gastrointestinal tract, and compound 35 was incubated with human liver microsomes to determine susceptibility to hepatic metabolism. Finally, compound 35 was evaluated in an uncomplicated MRSA skin infection mouse model and an MRSA neutropenic thigh infection mouse model.

RESULTS

Compound 35 inhibited the growth of MRSA clinical isolates at 2-4μM and was non-toxic to human keratinocytes. No resistance formation was observed with MRSA against compound 35 after 10 serial passages. In a murine skin wound model, compound 35 significantly reduced the burden of MRSA, similar to the antibiotic fusidic acid. Compound 35 exhibited a marked improvement both in permeability and stability to hepatic metabolism (half-life >11h) relative to the first-generation lead compound. In a neutropenic thigh infection mouse model, compound 35 successfully reduced the burden of MRSA in immunocompromised mice.

CONCLUSION

In summary, compound 35 was identified as a new lead aryl isonitrile compound that warrants further investigation as a novel antibacterial agent.

Evaluation of vancomycin use in university-affiliated hospitals in Southern Khorasan Province (East Iran) based on HICPAC guidelines

Background

Vancomycin resistance has raised concerns about its effectiveness prospect in the treatment of patients with Gram-positive infections. The Healthcare Infection Control Practices Advisory Committee (HICPAC) has recently established guidelines to delineate improper use of vancomycin. In this light, we sought out to determine the appropriateness of vancomycin prescription using the HICPAC guidelines.

Setting

The study was carried out in two university-affiliated hospitals, Valiasr and Imam Reza, with 297 and 234 beds, respectively, from May 2012 to May 2013.

Methods

This retrospective study evaluated the vancomycin prescription and usage in the hospitals. Total vancomycin use was determined and expressed as vancomycin courses per 298 admitted patients. The patient information was collected on a data collection sheet as follows: demographic variables, etiology and localization of infection, microbiological data, duration of vancomycin treatment, reasons for vancomycin prescription, prescribed antibiotic dosing, and patient regimen.

Results

The average age of the patients and vancomycin treatment duration were 55.965 years and 10.5 days, respectively. Septicemia (15.7%) was the most common cause of vancomycin administration. Vancomycin use was documented to be appropriate and inappropriate in 236 (89.4%) and 28 (10.6%) patients, respectively. No statistically significant differences were found among the wards and hospitals (P values =0.66 and 0.54, respectively) in terms of appropriateness of vancomycin use based on the HICPAC criteria. In addition, 29.21% and 62% of all patients exhibited complete and partial recovery, respectively. We found that 90% of the cases showed compliance with the HICPAC recommendations.

Conclusion

Comprehensive programs are required to improve the vancomycin use in the hospitals. Vancomycin use should be monitored due to its large-scale empiric use. The rate of improper use of vancomycin in the infection and intensive care unit services may be high, and pharmacists must take appropriate action to optimize the use of the drug.

Antibacterial activity of synthetic 1,3-bis(aryloxy)propan-2-amines against Gram-positive bacteria

Synthetic 1,3‐bis(aryloxy)propan‐2‐amines have been shown in previous studies to possess several biological activities, such as antifungal and antiprotozoal. In the present study, we describe the antibacterial activity of new synthetic 1,3‐bis(aryloxy)propan‐2‐amines against Gram‐positive pathogens (Streptococcus pyogenes, Enterococcus faecalis and Staphylococcus aureus) including Methicillin–resistant S. aureus strains. Our compounds showed minimal inhibitory concentrations (MIC) in the range of 2.5–10 μg/ml (5.99–28.58 μM), against different bacterial strains. The minimal bactericidal concentrations found were similar to MIC, suggesting a bactericidal mechanism of action of these compounds. Furthermore, possible molecular targets were suggested by chemical similarity search followed by docking approaches. Our compounds are similar to known ligands targeting the cell division protein FtsZ, Quinolone resistance protein norA and the Enoyl‐[acyl‐carrier‐protein] reductase FabI. Taken together, our data show that synthetic 1,3‐bis(aryloxy)propan‐2‐amines are active against Gram‐positive bacteria, including multidrug–resistant strains and can be a promising lead in the development of new antibacterial compounds for the treatment of these infections.

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.

tert-Butylphenylthiazoles with an oxadiazole linker: a novel orally bioavailable class of antibiotics exhibiting antibiofilm activity

The structure–activity and structure–kinetic relationships of a new tert-butylphenylthiazole series with oxadiazole linkers were conducted with the objective of obtaining a new orally available antibacterial compounds. Twenty-two new compounds were prepared, purified and identified. Their activity against methicillin-resistant Staphylococcus aureus were examined. Compound 20 with 3-hydroxyazetidine as a nitrogenous side chain showed promising activity against twenty-four clinical isolates, including vancomycin-resistant staphylococcal and enterococcal species with MIC values ranging from 4–8 μg mL⁻¹. Additional advantages of this compound include an ability to eradicate staphylococcal biofilm mass in a dose-dependent manner as well as high metabolic stability after an oral dose of 25 mg kg⁻¹ with a biological half-life that exceeds 5 hours and a plasma concentration (C_max) that exceeds the MIC values.

The structure–activity and structure–kinetic relationships of a new tert-butylphenylthiazole series with oxadiazole linkers were conducted with the objective of obtaining a new orally available antibacterial compounds.

Naphthylthiazoles: Targeting Multidrug-Resistant and Intracellular Staphylococcus aureus with Biofilm Disruption Activity

Thirty-two new naphthylthiazole derivatives were synthesized with the aim of exploring their antimicrobial effect on multidrug-resistant Gram-positive bacteria. Compounds 25 and 32, with ethylenediamine and methylguanidine side chains, represent the most promising derivatives, as their antibacterial spectrum includes activity against multidrug-resistant staphylococcal and enterococcal strains. Moreover, the new derivatives are highly advantageous over the existing frontline therapeutics for the treatment of multidrug-resistant Gram-positive bacteria. In this vein, compound 25 possesses three attributes: no bacterial resistance was developed against it even after 15 passages, it was very efficient in targeting intracellular pathogens, and it exhibited a concentration-dependent ability to disrupt the preformed bacterial biofilm.

Phenylthiazoles with tert-Butyl side chain: Metabolically stable with anti-biofilm activity

A new series of phenylthiazoles with t-butyl lipophilic component was synthesized and their antibacterial activity against a panel of multidrug-resistant bacterial pathogens was evaluated. Five compounds demonstrated promising antibacterial activity against methicillin-resistant staphylococcal strains and several vancomycin-resistant staphylococcal and enterococcal species. Additionally, three derivatives 19, 23 and 26 exhibited rapid bactericidal activity, and remarkable ability to disrupt mature biofilm produced by MRSA USA300. More importantly, a resistant mutant to 19 couldn't be isolated after subjecting MRSA to sub-lethal doses for 14 days. Lastly, this new series of phenylthiazoles possesses an advantageous attribute over the first-generation compounds in their stability to hepatic metabolism, with a biological half-life of more than 9 h.

Alkynyl-containing phenylthiazoles: Systemically active antibacterial agents effective against methicillin-resistant Staphylococcus aureus (MRSA)

The promising activity of phenylthiazoles against multidrug-resistant bacterial pathogens, in particular MRSA, has been hampered by their limited systemic applicability, due to their rapid metabolism by hepatic microsomal enzymes, resulting in short half-lives. Here, we investigated a series of phenylthiazoles with alkynyl side-chains that were synthesized with the objective of improving stability to hepatic metabolism, extending the utility of phenylthiazoles from topical applications to treatment of a more invasive, systemic MRSA infections. The most promising compounds inhibited the growth of clinically-relevant isolates of MRSA in vitro at concentrations as low as 0.5 μg/mL, and exerted their antibacterial effect by interfering with bacterial cell wall synthesis via inhibition of undecaprenyl diphosphate synthase and undecaprenyl diphosphate phosphatase. We also identified two phenylthiazoles that successfully eradicated MRSA inside infected macrophages. In vivo PK analysis of compound 9 revealed promising stability to hepatic metabolism with a biological half-life of ∼4.5 h. In mice, compound 9 demonstrated comparable potency to vancomycin, and at a lower dose (20 mg/kg versus 50 mg/kg), in reducing the burden of MRSA in a systemic, deep-tissue infection, using the neutropenic mouse thigh-infection model. Compound 9 thus represents a new phenylthiazole lead for the treatment of MRSA infections that warrants further development.

Biphenylthiazole antibiotics with an oxadiazole linker: An approach to improve physicochemical properties and oral bioavailability

A new series of oxadiazolylbiphenylthiazoles was prepared with the objective of improving the limited solubility of first-generation derivatives while maintaining antibacterial activity against drug-resistant Staphylococcus aureus. Studying the structure-activity relationship at the cationic part provided the piperazine-1-carboximidamide derivative 27 with a MIC (MRSA) value of 1.1 μg/mL, bactericidal mode of action, and a 50-fold improvement in aqueous solubility. Additionally, 27 exhibited a wider safety margin against mammalian cells, and most importantly, a significant improvement in oral bioavailability.

Arylthiazole antibiotics targeting intracellular methicillin-resistant Staphylococcus aureus (MRSA) that interfere with bacterial cell wall synthesis

The promising antibacterial potency of arylthiazole antibiotics is offset by their limited activity against intracellular bacteria (namely methicillin-resistant Staphylococcus aureus (MRSA)), similar to many clinically-approved antibiotics. The failure to target these hidden pathogens is due to the compounds' lack of proper characteristics to accumulate intracellularly. Fine tuning of the size and polar-surface-area of the linking heteroaromatic ring provided a new series of 5-thiazolylarylthiazoles with balanced properties that allow them to sufficiently cross and accumulate inside macrophages infected with MRSA. The most promising compound 4i exhibited rapid bactericidal activity, good metabolic stability and produced over 80% reduction of intracellular MRSA in infected macrophages.