Membrane-Active Hydantoin Derivatives as Antibiotic Agents

Discovery of membrane-targeting amphiphilic honokiol derivatives containing an oxazolethione moiety to combat methicillin-resistant Staphylococcus aureus (MRSA) infections

Methicillin-resistant Staphylococcus aureus (MRSA) has emerged as a major pathogen causing infections in hospitals and the community, and there is an urgent need for the development of novel antibacterials to combat MRSA infections. Herein, a series of amphiphilic honokiol derivatives containing an oxazolethione moiety were prepared and evaluated for their in vitro antibacterial and hemolytic activities. The screened optimal derivative, I3, exhibited potent in vitro antibacterial activity against S. aureus and clinical MRSA isolates with MIC values of 2-4 μg/mL, which was superior to vancomycin in terms of its rapid bactericidal properties and was less susceptible to the development of resistance. The SARs analysis indicated that amphiphilic honokiol derivatives with fluorine substituents had better antibacterial activity than those with chlorine and bromine substituents. In vitro and in vivo toxicity studies revealed that I3 has relatively low toxicity. In a MRSA-infected mouse skin abscess model, I3 (5 mg/kg) effectively killed MRSA at the infected site and attenuated the inflammation effects, comparable to vancomycin. In a MRSA-infected mouse sepsis model, I3 (12 mg/kg) was found to significantly reduce the bacterial load in infected mice and increase survival of infected mice. Mechanistic studies indicated that I3 has membrane targeting properties and can interact with phosphatidylglycerol (PG) and cardiolipin (CL) of MRSA cell membranes, thereby disrupting MRSA cell membranes, further inducing the increase of reactive oxygen species (ROS), protein and DNA leakage to achieve rapid bactericidal effects. Finally, we hope that I3 is a potential candidate molecule for the development of antibiotics to conquer superbacteria-related infections.

Hydantoin derivative dimers as broad-spectrum antimicrobial agents against ESKAPE pathogens with enhanced killing rate and stability

A new series of hydantoin derivative dimers as potential broad-spectrum antibiotic agents is designed and synthesized to combat ESKAPE pathogens. As membrane-active antimicrobial agents, in addition to cationic charged and hydrophobic groups that mimic AMPs (antimicrobial peptides), hydantoin backbones and aromatic linkers increased the rigidity and lipophilicity of the designed compounds, thus improving the stability and bactericidal killing rate. After whole cell phenotypic screening against eight bacterial strains, including MRSA (methicillin-resistant S. aureus), compound 18 was chosen as the lead compound with overall excellent broad-spectrum antibacterial activity (GM = 7.32 μg mL-1) and good selectivity. Kill-kinetic studies of compound 18 showed that the bacterial growth of both Gram-positive and Gram-negative was completely inhibited within one hour, which demonstrated excellent sterilization efficiency of 18. Furthermore, drug resistance and mechanism studies showed that compound 18 exhibited a steady antibacterial performance during 25 passages and could disrupt bacterial cell membrane integrity and cause cell death. Along with the facile synthesis procedures in solution, this series of hydantoin derivative dimer compounds could be an appealing next generation of antibiotic agents to combat emergent drug resistance.

Therapeutic potential of hydantoin and thiohydantoin compounds against Schistosoma mansoni: An integrated in vitro, DNA, ultrastructural, and ADMET in silico approach

The study aimed to conduct in vitro biological assessments of hydantoin and thiohydantoin compounds against mature Schistosoma mansoni worms, evaluate their cytotoxic effects and predict their pharmacokinetic parameters using computational methods. The compounds showed low in vitro cytotoxicity and were not considered hemolytic. Antiparasitic activity against adult S. mansoni worms was tested with all compounds at concentrations ranging from 200 to 6.25 μM. Compounds SC01, SC02, and SC03 exhibited low activity. Compounds SC04, SC05, SC06 and SC07 caused 100 % mortality within 24 h of incubation at a concentration of 100 and 200 μM. Thiohydantoin SC04 exhibited the highest activity, resulting in 100 % mortality after 24 h of incubation at a concentration of 50 μM and IC50 of 28 µM. In the ultrastructural analysis (SEM), the compound SC04 (200 µM) induced integumentary changes, formation of integumentary blisters, and destruction of tubercles and spicules. Therefore, the SC04 compound shows promise as an antiparasitic against S. mansoni.

Synthesis and biological evaluation of hydantoin derivatives as potent antiplasmodial agents

Malaria, a devastating disease, has claimed numerous lives and caused considerable suffering, with young children and pregnant women being the most severely affected group. However, the emergence of multidrug-resistant strains of Plasmodium and the adverse side effects associated with existing antimalarial drugs underscore the urgent need for the development of novel, well-tolerated, and more efficient drugs to combat this global health threat. To address these challenges, six new hydantoins derivatives were synthesized and evaluated for their in vitro antiplasmodial activity. Notably, compound 2c exhibited excellent inhibitory activity against the tested Pf3D7 strain, with an IC50 value of 3.97 ± 0.01 nM, three-fold better than chloroquine. Following closely, compound 3b demonstrated an IC50 value of 27.52 ± 3.37 µM against the Pf3D7 strain in vitro. Additionally, all the hydantoins derivatives tested showed inactive against human MCR-5 cells, with an IC50 value exceeding 100 μM. In summary, the hydantoin derivative 2c emerges as a promising candidate for further exploration as an antiplasmodial compound.

Reversing Anticancer Drug Resistance by Synergistic Combination of Chemotherapeutics and Membranolytic Antitumor β-Peptide Polymer

Multidrug resistance is the main obstacle to cancer chemotherapy. Overexpression of drug efflux pumps causes excessive drug efflux from cancer cells, ultimately leading to drug resistance. Hereby, we raise an effective strategy to overcome multidrug resistance using a synergistic combination of membranolytic antitumor β-peptide polymer and chemotherapy drugs. This membrane-active β-peptide polymer promotes the transmembrane transport of chemotherapeutic drugs by increasing membrane permeability and enhances the activity of chemotherapy drugs against multidrug-resistant cancer cells. As a proof-of-concept demonstration, the synergistic combination of β-peptide polymer and doxorubicin (DOX) is substantially more effective than DOX alone against drug-resistant cancer both in vitro and in vivo. Notably, the synergistic combination maintains a potent anticancer activity after continuous use. Collectively, this combination therapy using membrane lytic β-peptide polymer appears to be an effective strategy to reverse anticancer drug resistance.

Cell-Selective Binding Zwitterionic Polymeric Micelles Boost the Delivery Efficiency of Antibiotics

Effective accumulation and penetration of antibiotics in the biofilm are critical issues for bacterial infection treatment. Red blood cells (RBCs) have been widely utilized to hitchhike nanocarriers for drug delivery. It is vital and challenging to find a nanocarrier with an appropriate affinity toward RBCs and bacteria for selective hitchhiking and release that determines the drug delivery efficiency and specificity. Herein, we report a zwitterionic polymer poly(2-(N-oxide-N,N-diethylamino)ethyl methacrylate) (OPDEA)-based micelle, which can hitchhike on RBCs in blood and preferentially release in the infection site. We found that OPDEA could bind to the RBCs cell membrane via phospholipid-related affinity and transfer to Gram-positive bacteria due to nearly an order of magnitude stronger interaction with the bacteria cell wall. The zwitterionic surface and cell-wall affinity of OPDEA-based micelles also promote their penetration in biofilm. The clarithromycin-loaded OPDEA micelles show efficient drug delivery into the infection site, resulting in excellent therapeutic performance in both peritonitis and pneumonia models by intravenous or spray administration. This simple RBC-selective hitchhiking and releasing antibiotic delivery system provides a promising strategy for the design of antibacterial nanomedicines.

Design and synthesis of broad-spectrum antimicrobial amphiphilic peptidomimetics to combat drug-resistance

The gradual depletion of antibiotic discovery pipeline makes the antibiotic resistance a difficult clinical problem and a global health emergency. The membrane-active antimicrobial peptides (AMPs) attracted much attention due to a lower tendency to bacterial resistance than traditional antibiotics. However, some immanent drawbacks of AMPs may hamper their application in combating antibiotic resistance in the long run, such as susceptible to enzymatic degradation and low cell permeability. Herein, we report the design and synthesis of a novel series of amphiphilic peptidomimetics, from which we identified compounds that exhibited potent antimicrobial activity against a panel of clinically relevant Gram-positive and Gram-negative bacteria strains. The most potent compound 20 (SD-110-12) is able to kill intracellular bacterial pathogens and prevent the development of bacterial resistance under the tested conditions by targeting cell membranes. Additionally, compound 20 (SD-110-12) obtains good in vivo efficacy that is comparative to vancomycin by eradicating MRSA and suppressing inflammation in a mice infected skin wound model, demonstrating its promising therapeutic potential.

Kevlar®, Nomex®, and VAR Modification by Small Organic Molecules Anchoring: Transfusing Antibacterial Properties and Improving Water Repellency

The surface modification of fabrics composed of Kevlar^®, Nomex^®, or VAR was extensively investigated. Kevlar^® and Nomex^® are widely-utilized aramid materials, whereas VAR is a technical fabric comprising 64% viscose, 24% para-aramid (Kevlar^®), 10% polyamide, and 2% antistatic fibers. Both aramid materials and cellulose/viscose exhibit exceptional mechanical properties that render them valuable in a wide range of applications. For the herein studied modification of Kevlar^®, Nomex^®, and VAR, we used small organic molecules 3-allyl-5,5-dimethylhydantoin (ADMH) and 3-(acrylamidopropyl)trimethylammonium chloride (APTAC), which were anchored onto the materials under study via graft polymerization. By doing so, excellent antibacterial properties were induced in the three studied fabrics. Their water repellency was improved in most cases as well. Extensive characterization studies were conducted to probe the properties of the modified materials, employing Raman and FTIR spectroscopies, Scanning Electron Microscopy (SEM), and thermogravimetric analysis (TGA).

Antimicrobial Peptides and Small Molecules Targeting the Cell Membrane of Staphylococcus aureus

Clinical management of Staphylococcus aureus infections presents a challenge due to the high incidence, considerable virulence, and emergence of drug resistance mechanisms. The treatment of drug-resistant strains, such as methicillin-resistant S. aureus (MRSA), is further complicated by the development of tolerance and persistence to antimicrobial agents in clinical use. To address these challenges, membrane disruptors, that are not generally considered during drug discovery for agents against S. aureus, should be explored. The cell membrane protects S. aureus from external stresses and antimicrobial agents, but membrane-targeting antimicrobial agents are probably less likely to promote bacterial resistance. Nontypical linear cationic antimicrobial peptides (AMPs), highly modified AMPs such as daptomycin (lipopeptide), bacitracin (cyclic peptide), and gramicidin S (cyclic peptide), are currently in clinical use. Recent studies have demonstrated that AMPs and small molecules can penetrate the cell membrane of S. aureus, inhibit phospholipid biosynthesis, or block the passage of solutes between the periplasm and the exterior of the cell. In addition to their primary mechanism of action (MOA) that targets the bacterial membrane, AMPs and small molecules may also impact bacteria through secondary mechanisms such as targeting the biofilm, and downregulating virulence genes of S. aureus. In this review, we discuss the current state of research into cell membrane-targeting AMPs and small molecules and their potential mechanisms of action against drug-resistant physiological forms of S. aureus, including persister cells and biofilms.

Investigation of Naphthyl-Polyamine Conjugates as Antimicrobials and Antibiotic Enhancers

As part of our search for new antimicrobials and antibiotic enhancers, a series of naphthyl- and biphenyl-substituted polyamine conjugates have been synthesized. The structurally-diverse library of compounds incorporated variation in the capping end groups and in the length of the polyamine (PA) core. Longer chain (PA-3-12-3) variants containing both 1-naphthyl and 2-naphthyl capping groups exhibited more pronounced intrinsic antimicrobial properties against methicillin-resistant Staphylococcus aureus (MRSA) (MIC ≤ 0.29 µM) and the fungus Cryptococcus neoformans (MIC ≤ 0.29 µM). Closer mechanistic study of one of these analogues, 20f, identified it as a bactericide. In contrast to previously reported diarylacyl-substituted polyamines, several examples in the current set were able to enhance the antibiotic action of doxycycline and/or erythromycin towards the Gram-negative bacteria Pseudomonas aeruginosa and Escherichia coli. Two analogues (19a and 20c) were of note, exhibiting greater than 32-fold enhancement in activity. This latter result suggests that α,ω-disubstituted polyamines bearing 1-naphthyl- and 2-naphthyl-capping groups are worthy of further investigation and optimization as non-toxic antibiotic enhancers.

Structural identification of pyridinopyrone compounds with anti-neuroinflammatory activity from streptomyces sulphureus DSM 40104

This study investigated the chemical composition and biosynthesis pathway of compounds produced by Streptomyces sulphureus DSM 40104. With the guild of molecular networking analysis, we isolated and identified six uncommon structural characteristics of compounds, including four newly discovered pyridinopyrones. Based on genomic analysis, we proposed a possible hybrid NRPS-PKS biosynthesis pathway for pyridinopyrones. Notably, this pathway starts with the use of nicotinic acid as the starting unit, which is a unique feature. Compounds 1-3 exhibited moderate anti-neuroinflammatory activity against LPS-induced BV-2 cell inflammation. Our study demonstrates the diversity of polyene pyrone compounds regarding their chemical structure and bioactivity while providing new insights into their biosynthesis pathway. These findings may lead to the development of new treatments for inflammation-related diseases.

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

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

Development of Aromatic-Linked Diamino Acid Antimicrobial Peptide Mimics with Low Hemolytic Toxicity and Excellent Activity against Methicillin-Resistant Staphylococcus aureus (MRSA)

Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) have become one of the biggest threats to public health. To develop new antibacterial agents against MRSA, a series of diamino acid compounds with aromatic nuclei linkers were designed and synthesized. Compound 8j, which exhibited low hemolytic toxicity and the best selectivity against S. aureus (SI > 2000), showed good activity against clinical MRSA isolates (MIC = 0.5-2 μg/mL). Compound 8j was able to quickly kill bacteria without inducing bacterial resistance. A mechanistic study and transcriptome analysis revealed that compound 8j can act on phosphatidylglycerol and induce the accumulation of endogenous reactive oxygen species, which can destroy bacterial membranes. Importantly, compound 8j achieved a 2.75 log reduction of MRSA count at 10 mg/kg/d in a mouse subcutaneous infection model. These findings suggested that compound 8j had the potential to be an antibacterial agent against MRSA.

Investigation of tetrasubstituted heterocycles reveals hydantoins as a promising scaffold for development of novel antimicrobials with membranolytic properties

Mimics of antimicrobial peptides (AMPs) have been proposed as a promising class of antimicrobial agents. We report the analysis of five tetrasubstituted, cationic, amphipathic heterocycles as potential AMP mimics. The analysis showed that the heterocyclic scaffold had a strong influence on the haemolytic activity of the compounds, and the hydantoin scaffold was identified as a promising template for drug lead development. Subsequently, a total of 20 hydantoin derivatives were studied for their antimicrobial potency and haemolytic activity. We found 19 of these derivatives to have very low haemolytic toxicity and identified three lead structures, 2dA, 6cG, and 6dG with very promising broad-spectrum antimicrobial activity. Lead structure 6dG displayed minimum inhibitory concentration (MIC) values as low as 1 μg/mL against Gram-positive bacteria and 4-16 μg/mL against Gram-negative bacteria. Initial mode of action (MoA) studies performed on the amine derivative 6cG, utilizing a luciferase-based biosensor assay, suggested a strong membrane disrupting effect on the outer and inner membrane of Escherichia coli. Our findings show that the physical properties and structural arrangement induced by the heterocyclic scaffolds are important factors in the design of AMP mimics.

A metalloporphyrin and hydantoin functionalized nanozyme with synergistically enhanced bacterial inhibition

An elaborate design of multimodal antibacterial agents has been revealed to be a promising strategy to address bacterial resistance, originating from the abuse of antibiotics. In this work, we have developed a positively charged and porous material, FePPOP_Hydantoin, as a disinfectant via introducing 1,3-dibromo-5,5-dimethylhydantoin (Hydantoin) and porphyrin iron units into a polymer framework. The extended π conjugated networks of FePPOP_Hydantoin endowed the material with strong near-infrared (NIR) absorption, high density of surface catalytic active centers, superior stability, and reproducibility. FePPOP_Hydantoin exhibits high peroxidase mimetic and photo-Fenton activity, which can catalyze the biologically allowable maximum concentrations of hydrogen peroxide (100 μM) to produce a vast amount of hydroxyl radicals. Simultaneously, the effective electrostatic interaction between the positively charged FePPOP_Hydantoin and the negatively charged bacteria facilitates the binding of FePPOP_Hydantoin on the bacterial membrane, restricting bacteria within the destruction range of hydroxyl radicals and thus making the bacteria more vulnerable. Finally, further close contact between bacteria and Hydantoin units in FePPOP_Hydantoin gave the material an antibacterial efficiency of over 99.999%. Compared with chemical therapy, photo-Fenton therapy, or peroxidase catalytic therapy alone, FePPOP_Hydantoin had a noteworthy multi-amplified antibacterial efficiency. Furthermore, FePPOP_Hydantoin exhibited good biocompatibility and negligible cytotoxicity. The in vivo antibacterial therapy on the Staphylococcus aureus (S. aureus) infected mouse wound model clearly proved the effectiveness of FePPOP_Hydantoin for fighting bacterial infections. This work highlights opportunities for the design of nanozymes with enhanced bacteriostatic activity, providing a new avenue for the construction of novel antibiotics.

Small Molecular Mimetics of Antimicrobial Peptides as a Promising Therapy To Combat Bacterial Resistance

Clinically, antibiotics are widely used to treat infectious diseases; however, excessive drug abuse and overuse exacerbate the prevalence of drug-resistant bacterial pathogens, making the development of novel antibiotics extremely difficult. Antimicrobial peptide (AMP) is one of the most promising candidates for overcoming bacterial resistance owing to its unique structure and mechanism of action. This study examines the development of small molecular mimetics of AMPs over the past two decades. These mimetics can selectively disrupt membranes, which are the characteristic antibacterial mechanism of AMPs. In addition, the advantages and disadvantages of small AMP mimetics are discussed. The small molecular mimetics of AMPs are anticipated to garner interest and investment in discovering new antibiotics. This Perspective will assist in revitalizing the golden age of antibiotics in the current era of combating bacterial resistance.

Biologically Oriented Hybrids of Indole and Hydantoin Derivatives

Indoles and hydantoins are important heterocycles scaffolds which present in numerous bioactive compounds which possess various biological activities. Moreover, they are essential building blocks in organic synthesis, particularly for the preparation of important hybrid molecules. The series of hybrid compounds containing indoles and imidazolidin-2-one moiety with direct C-C bond were synthesized using an amidoalkylation one-pot reaction. All compounds were investigated as a growth regulator for germination, growth and development of wheat seeds (Triticum aestivum L). Their effect on drought resistance at very low concentrations (4 × 10^-5 M) was evaluated. The study highlighted identified the leading compounds, 3a and 3e, with higher growth-regulating activity than the indole-auxin analogues.

Membrane-Targeting Neolignan-Antimicrobial Peptide Mimic Conjugates to Combat Methicillin-Resistant Staphylococcus aureus (MRSA) Infections

Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) continue to endanger public health. Here, we report the synthesis of neolignan isomagnolone (I) and its isomer II, and the preparation of a series of novel neolignan-antimicrobial peptide (AMP) mimic conjugates. Notably, conjugates III5 and III15 exhibit potent anti-MRSA activity in vitro and in vivo, comparable to that of vancomycin, a current effective treatment for MRSA. Moreover, III5 and III15 display not only fast-killing kinetics and low resistance frequency but also low toxicity as well as effects on bacterial biofilms. Mechanism studies reveal that III5 and III15 exhibit rapid bactericidal effects through binding to the phosphatidylglycerol (PG) and cardiolipin (CL) of the bacterial membrane, thereby disrupting the cell membranes and allowing increased reactive oxygen species (ROS) as well as protein and DNA leakage. The results indicate that these neolignan-AMP mimic conjugates could be promising antimicrobial candidates for combating MRSA infections.

Identification of 5-(Aryl/Heteroaryl)amino-4-quinolones as Potent Membrane-Disrupting Agents to Combat Antibiotic-Resistant Gram-Positive Bacteria

Nosocomial infections caused by resistant Gram-positive organisms are on the rise, presumably due to a combination of factors including prolonged hospital exposure, increased use of invasive procedures, and pervasive antibiotic therapy. Although antibiotic stewardship and infection control measures are helpful, newer agents against multidrug-resistant (MDR) Gram-positive bacteria are urgently needed. Here, we describe our efforts that led to the identification of 5-amino-4-quinolone 111 with exceptionally potent Gram-positive activity with minimum inhibitory concentrations (MICs) ≤0.06 μg/mL against numerous clinical isolates. Preliminary mechanism of action and resistance studies demonstrate that the 5-amino-4-quinolones are bacteriostatic, do not select for resistance, and selectively disrupt bacterial membranes. While the precise molecular mechanism has not been elucidated, the lead compound is nontoxic displaying a therapeutic index greater than 500, is devoid of hemolytic activity, and has attractive physicochemical properties (clog P = 3.8, molecular weight (MW) = 441) that warrant further investigation of this promising antibacterial scaffold for the treatment of Gram-positive infections.

N-Arylimidazoliums as Highly Selective Biomimetic Antimicrobial Agents

Antibiotic resistance has become one of the greatest health threats in the world. In this study, a charge-dispersed dimerization strategy is described for the antimicrobial peptide (AMP) mimics via a tunable cationic charge to improve the selectivity between prokaryotic microbes and eukaryotic cells. This strategy is demonstrated with a series of charge-dispersed AMP mimics based on N-arylimidazolium skeletons. These N-arylimidazolium AMP mimics show potent antibacterial activity against strains along with a low rate of drug resistance, good hemocompatibility, and low cytotoxicity. In addition to the elimination of planktonic bacteria, N-arylimidazolium AMP mimics can also inhibit biofilm formation and destroy the established biofilm. More importantly, methicillin-resistant Staphylococcus aureus (MRSA)-induced lung-infected mice can be effectively treated by the intravenous administration of N-arylimidazolium AMP mimic, which enable the design of N-arylimidazolium AMP mimics to offer an alternative avenue to eradicate drug-resistant bacterial infection.

Effect of New 2-Thioxoimidazolidin-4-one Compounds against Staphylococcus aureus Clinical Strains and Immunological Markers’ Combinations

Although the structure-activity relationship indicates that the 4-thioxoimidazolidin ring is essential for antibacterial activities and pharmaceutical applications, there were no enough studies on the derivatives of this compound. Evaluating the new hydantoin compounds C5 (3-((2-bromobenzylidene) amino)-2- thioxoimidazolidin-4-one) and C6 (3-((4- methoxybenzylidene) amino)-2-thioxoimidazolidin-4-one) that were prepared against clinical Staphylococcus aureus isolates for antibacterial, antibiofilm, and antihemagglutination activities is the aim of this study. Therefore, the potential clinical resistance of the strains was evaluated by their ability to form biofilms, antibiotic resistance, and agglutinate erythrocytes macroscopically and microscopically; besides, the bacterial biofilm was screened for any association with the patient's serum immunoglobulin levels and complements. Despite the effective concentration for C5 and C6 compounds, which is ≤ 31.25 μg/ml, the reduction rate is not concentration-dependent; it depends on the molecular docking of the hydantoin compounds. Hence, the effect of the minimal inhibitory concentrations (MICs) is variable. In this study, the results for the compounds (with the concentration of 31.25–62.5 μg/mL for C5 and 62.5–125 μg/mL for C6) significantly manifest the antibacteria, antibiofilm, and antihemagglutination effects against the virulent strains of S. aureus due to the high percentage of biofilm inhibition that was caused by the new hydantoin compounds. Besides, time-kill kinetics studies showed that these compounds pose bactericidal action. Overall, this study revealed that the new hydantoin derivatives have an interesting potential as new antibacterial drugs through the inhibition of bacterial adhesion. The infections of these isolates activate the complement system through the lectin pathway. Nevertheless, these compounds can be improved in order to be used at even lower concentrations.

Design, synthesis, and biological evaluation of membrane-active honokiol derivatives as potent antibacterial agents

Infections caused by drug-resistant bacteria have emerged to be one of the greatest threats to global public health, and new antimicrobial agents with novel mechanisms of action hence are in an urgent need to combat bacterial resistance. Herein, we reported the design, synthesis, and antibacterial evaluation of novel honokiol derivatives as mimics of antimicrobial peptides (AMPs). These mimics showed potent antimicrobial properties against Gram-positive bacteria. Among them, the most promising compound 13b exhibited excellent antibacterial activity, rapid bactericidal properties, avoidance of antibiotic resistance, and weak hemolytic and cytotoxic activities. In addition, compound 13b not only inhibited the biofilm formation but also destroy the preformed biofilm. Mechanism studies further revealed that compound 13b killed bacteria rapidly by interrupting the bacterial membrane. More intriguingly, compound 13b exhibited potent in vivo antibacterial efficacy in a mouse septicemia model induced by Staphylococcus aureus ATCC43300. These results highlight the potential of 13b to be used as therapeutic agents.

Antimicrobial Peptide Mimics for Clinical Use: Does Size Matter?

The search for efficient antimicrobial therapies that can alleviate suffering caused by infections from resistant bacteria is more urgent than ever before. Infections caused by multi-resistant pathogens represent a significant and increasing burden to healthcare and society and researcher are investigating new classes of bioactive compounds to slow down this development. Antimicrobial peptides from the innate immune system represent one promising class that offers a potential solution to the antibiotic resistance problem due to their mode of action on the microbial membranes. However, challenges associated with pharmacokinetics, bioavailability and off-target toxicity are slowing down the advancement and use of innate defensive peptides. Improving the therapeutic properties of these peptides is a strategy for reducing the clinical limitations and synthetic mimics of antimicrobial peptides are emerging as a promising class of molecules for a variety of antimicrobial applications. These compounds can be made significantly shorter while maintaining, or even improving antimicrobial properties, and several downsized synthetic mimics are now in clinical development for a range of infectious diseases. A variety of strategies can be employed to prepare these small compounds and this review describes the different compounds developed to date by adhering to a minimum pharmacophore based on an amphiphilic balance between cationic charge and hydrophobicity. These compounds can be made as small as dipeptides, circumventing the need for large compounds with elaborate three-dimensional structures to generate simplified and potent antimicrobial mimics for a range of medical applications. This review highlight key and recent development in the field of small antimicrobial peptide mimics as a promising class of antimicrobials, illustrating just how small you can go.

Synthesis and biological activity of novel hydantoin cyclohexyl sulfonamide derivatives as potential antimicrobial agents in agriculture

BACKGROUND

Plant disease is one of the most serious problems in agriculture that can damage crops. Chemical fungicides are widely used to control plant diseases, but have led to resistance and a series of environmental problems. It is, therefore, necessary to develop highly effective and eco-friendly antimicrobial compounds with novel structures.

RESULTS

A series of novel hydantoin cyclohexyl sulfonamide derivatives were synthesized through an intramolecular condensation reaction. The bioassay results indicated that a majority of the title compounds displayed potent inhibitory activity against Botrytis cinerea, Sclerotinia sclerotiorum and Erwinia carotorora. The in vivo inhibition rate of compound 3h was 91.01% against B. cinerea, which was higher than that of iprodione (84.07%). Compound 3w showed excellent antifungal activity against B. cinerea with a half-maximal effective concentration (EC₅₀ ) of 4.80 μg ml^-1 , which is lower than that of iprodione. Compound 3q had an EC₅₀ value of 1.44 μg ml^-1 against S. sclerotiorum, which was close to that of iprodione (1.39 μg ml^-1 ), and the inhibition rate was also similar to that of iprodione. Compounds 3i and 3w had the best inhibition efficacy against S. sclerotiorum, both on growth of the mycelium and sclerotia and in the greenhouse pot test in vitro. Further study showed that compounds 3h, 3r and 3s have superb antibacterial activity against E. carotorora with EC₅₀ values of 2.65, 4.24 and 4.29 μg ml^-1 respectively, and were superior to streptomycin sulfate (5.96 μg ml^-1 ).

CONCLUSION

Because of their excellent antifungal and antibacterial activity against B. cinerea, S. sclerotiorum and E. carotorora, these hydantoin cyclohexyl sulfonamide derivatives could be considered as suitable candidates for new antimicrobial agents. © 2021 Society of Chemical Industry.

Molecular Dynamics Studies on the Bacterial Membrane Pore Formation by Small Molecule Antimicrobial Agents

Antimicrobial peptides (AMPs) act on the membrane bilayer of pathogens, causing leakage in the membrane and cell death. Amphiphilic kaempferol derivatives possessing basic functional groups show excellent antibacterial activities, which has been proven through experimental techniques. These compounds are known to target negatively charged bacterial membranes. However, the detailed mechanism of action and their structure-activity relationship are not clear. In this work, we reported theoretical investigation on the mechanism of action of two previously reported kaempferol derivatives on a DMPC/DMPG mixed bilayer. Despite the rigid structure of the compounds when compared to AMPs, spontaneous pore formation in the membrane was not observed in 400 ns molecular dynamics (MD) simulations. MD simulations with biasing forces resulted in the formation of pores in the bilayer for the derivatives and not for kaempferol. The stability of the pores was assessed by pore closure timescales in unbiased MD simulations, which was found to be 5.3 and 17.0 ns for 2 and 3, respectively. Free energy change for the permeation into the bilayer for kaempferol (1), tertiary amine derivative (2), and arginine derivative (3) was calculated to be -1.5, -48.2, and -100.3 kJ/mol, respectively, which correlate with their antibacterial activity. Furthermore, our results indicate that compound 3 forms a stable toroidal pore in the membrane when multiple molecules are oriented in a transmembrane configuration. Our work sheds light on the mechanism of action of small molecule antimicrobial agents, which can be exploited for the rational design of drug candidates.

Synthesis and bioactivities of new N-terminal dipeptide mimetics with aromatic amide moiety: Broad-spectrum antibacterial activity and high antineoplastic activity

The increasingly growing epidemics of multidrug-resistant bacteria are becoming severe public health threat. There is in an urgent need to develop new antibacterial agents with broad-spectrum antibacterial activity and high selectivity. Here, a series of N-terminal dipeptide mimetics with an aromatic amide moiety were synthesized from amino acids. The effects of amino acid type and aromatic moiety on the biological activities of the mimetics were evaluated. The dipeptide mimetics not only showed significant broad-spectrum antibacterial activity against Gram-negative (Escherichia coli and Klebsiella pneumoniae), Gram-positive (Staphylococcus aureus) and drug-resistant bacterium MRSA (methicillin-resistant S. aureus) but also demonstrated high selectivity for S. aureus versus mammalian erythrocytes. The coupling product of L-valine with p-alkynylaniline (dipeptide mimetic 7) exhibited the best antibacterial activities with minimum inhibitory concentration (MIC) ranging from 2.5 to 5 μg/mL. Moreover, the bactericidal kinetics and multi-passage resistance tests indicated that the mimetic 7 both rapidly killed bacteria and had a low probability of emergence of antimalarial resistance. Meanwhile, the mimetic 7 possessed the ability to both inhibit bacterial biofilm formation and eradicate mature biofilm. The depolarization and destruction of the bacterial cell membrane is the main sterilization mechanism, which hinders the propensity to develop bacterial resistance. Furthermore, the mimetic 7 also showed good antineoplastic activity against gastric cancer cell (SGC 7901, IC₅₀ = 70.8 μg/mL), while it had very low toxicity to mammalian cell (L929). The mimetics bear considerable potential to be used as antibacterial and anticancer agents to combat antibiotic resistance.

Development of Amphiphilic Coumarin Derivatives as Membrane-Active Antimicrobial Agents with Potent In Vivo Efficacy against Gram-Positive Pathogenic Bacteria

Increases in drug-resistant pathogens are becoming a serious detriment to human health. To combat pathogen infections, a new series of amphiphilic coumarin derivatives were designed and synthesized as antimicrobial agents with membrane-targeting action. We herein report a lead compound, 25, that displayed potent antibacterial activity against Gram-positive bacteria, including MRSA. Compound 25 exhibited weak hemolytic activity and low toxicity to mammalian cells and can kill Gram-positive bacteria quickly (within 0.5 h) by directly disrupting the bacterial cell membranes. Additionally, compound 25 demonstrated excellent efficacy in a murine corneal infection caused by Staphylococcus aureus. These results suggest that 25 has great potential to be a potent antimicrobial agent for treating drug-resistant Gram-positive bacterial infections.

Development of Membrane-Active Honokiol/Magnolol Amphiphiles as Potent Antibacterial Agents against Methicillin-Resistant Staphylococcus aureus (MRSA)

Currently, infections caused by drug-resistant bacteria have become a new challenge in anti-infective treatment, seriously endangering public health. In our continuous effort to develop new antimicrobials, a series of novel honokiol/magnolol amphiphiles were prepared by mimicking the chemical structures and antibacterial properties of cationic antimicrobial peptides. Among them, compound 5i showed excellent antibacterial activity against Gram-positive bacteria and clinical MRSA isolates (minimum inhibitory concentrations (MICs) = 0.5-2 μg/mL) with low hemolytic and cytotoxic activities and high membrane selectivity. Moreover, 5i exhibited rapid bactericidal properties, low resistance frequency, and good capabilities of disrupting bacterial biofilms. Mechanism studies revealed that 5i destroyed bacterial cell membranes, resulting in bacterial death. Additionally, 5i displayed high biosafety and potent in vivo anti-infective potency in a murine sepsis model. Our study indicates that these honokiol/magnolol amphiphiles shed light on developing novel antibacterial agents, and 5i is a potential antibacterial candidate for combating MRSA infections.

Design, Synthesis, and In Vitro Antiproliferative Activity of Hydantoin and Purine Derivatives with the 4-Acetylphenylpiperazinylalkyl Moiety

Cancer represents one of the most serious health problems and the second leading cause of death around the world. Heterocycles, due to their prevalence in nature as well as their structural and chemical diversity, play an immensely important role in anti-cancer drug discovery. In this paper, a series of hydantoin and purine derivatives containing a 4-acetylphenylpiperazinylalkyl moiety were designed, synthesized, and biologically evaluated for their anticancer activity on selected cancer cell lines (PC3, SW480, SW620). Compound 4, a derivative of 3′,4′-dihydro-2′H-spiro[imidazolidine-4,1′-naphthalene]-2,5-dione, was the most effective against SW480, SW620, and PC3 cancer cell lines. Moreover, 4 has high tumor-targeting selectivity. Based on docking studies, it was concluded that R isomers of 3′,4′-dihydro-2′H-spiro[imidazolidine-4,1′-naphthalene]-2,5-dione could be further studied as promising scaffolds for the development of thymidine phosphorylase inhibitors.

Modular Design of Membrane-Active Antibiotics: From Macromolecular Antimicrobials to Small Scorpionlike Peptidomimetics

Infections caused by multidrug-resistant bacteria have emerged in recent decades, leading to escalating interest in host defense peptides (HDPs) to reverse this dangerous trend. Inspired by the modular design in bioengineering, herein we report a new class of small amphiphilic scorpionlike peptidomimetics based on this strategy. These HDP mimics show potent antimicrobial activity against both Gram-positive and Gram-negative bacteria without drug resistance but with a high therapeutic index. The membrane-compromising action mode was suggested to be their potential bactericidal mechanism. Pharmacodynamic experiments were conducted using a murine abscess model of methicillin-resistant Staphylococcus aureus (MRSA) infections. The lead compound 12 showed impressive in vivo therapeutic efficacy with ∼99.998% (4.7log) reduction in skin MRSA burden, a significantly higher bactericidal efficiency than ciprofloxacin, and good biocompatibility. These results highlight the potential of these HDP mimics as novel antibiotic therapeutics.

In vitro and in vivo degradation of programmed cell death ligand 1 (PD-L1) by a proteolysis targeting chimera (PROTAC)

Immunotherapy via immune checkpoints blockade has aroused the attention of researchers worldwide. Inhibition of the programmed cell death-1 (PD-1)/programmed cell death-ligand 1 (PD-L1) interaction has been one of the most promising immunotherapy strategies. Several neutralizing antibodies targeting this interaction have been developed, which have already achieved considerable clinical success. Additionally, numerous pharmaceutical companies have been committed to develop small molecules which could block the interaction between PD-1 and PD-L1. In this study, a novel PROTAC molecule 21a was developed, and effectively induced the degradation of PD-L1 protein in various malignant cells in a proteasome-dependent manner. Moreover, compound 21a could significantly reduce PD-L1 protein levels of MC-38 cancer cells in vivo, by which promoted the invasion of CD8+ T cells and inhibited the growth of MC-38 in vivo. This PROTAC molecule could be used as a novel and alternative strategy for cancer immunotherapy.

Dimeric lipo-α/sulfono-γ-AA hybrid peptides as broad-spectrum antibiotic agents

There is an urgent need to develop novel antibiotic agents that can combat emerging drug resistance. Herein, we report the design and investigation of a class of short dimeric antimicrobial lipo-α/sulfono-γ-AA hybrid peptides. Some of these peptides exhibit potent and broad-spectrum antimicrobial activity toward both clinically related Gram-positive and Gram-negative bacteria. The TEM study suggests that these hybrid peptides can compromise bacterial membranes and lead to bacterial death. Membrane depolarization and fluorescence microscopy studies also indicate that the mechanism of action is analogous to host-defense peptides (HDPs). Furthermore, the lead compound shows the ability to effectively inhibit biofilms formed from MRSA and E. coli. Further development of the short dimeric lipo-α/sulfono-γ-AA hybrid peptides may lead to a new generation of antimicrobial biomaterials to combat drug resistance.

Design, Synthesis, and Biological Evaluation of Membrane-Active Bakuchiol Derivatives as Effective Broad-Spectrum Antibacterial Agents

Infections caused by drug-resistant bacteria seriously endanger human health and global public health. Therefore, it is urgent to discover and develop novel antimicrobial agents to combat multidrug-resistant bacteria. In this study, we designed and synthesized a series of new membrane-active bakuchiol derivatives by biomimicking the structure and function of cationic antibacterial peptides. The most promising compound 28 displayed potent antibacterial activity against both Gram-positive bacteria (minimum inhibitory concentration, MIC = 1.56-3.125 μg/mL) and Gram-negative bacteria (MIC = 3.125 μg/mL), very weak hemolytic activity, and low cytotoxicity. Compound 28 had rapid bactericidal properties and avoided bacterial resistance. More importantly, compound 28 showed strong in vivo antibacterial efficacy against Staphylococcus aureus and Pseudomonas aeruginosa in murine corneal infection models. This design strategy is expected to provide an effective solution to the antibiotic crisis.

A Cascade Approach for the Synthesis of 5-(Indol-3-yl)hydantoin: An Application to the Total Synthesis of (±)-Oxoaplysinopsin B

A cascade approach to the synthesis of 5-(indol-3-yl)hydantoin framework has been developed by the reaction of indole with glyoxylic acid/pyruvic acid under a deep eutectic solution, (+)-tartaric acid-dimethylurea. N,N'-Dimethylurea from a deep eutectic solution functions as a reactant as well as a solvent mixture. Isolation of the intermediate, 5-hydroxyhydantoin, and its reaction with indole provides the mechanistic evidence for this reaction. This method was successfully applied in the first total synthesis of an alkaloid, (±)-oxoaplysinopsin B, with an overall yield of 48%.

Recent advances in design of antimicrobial peptides and polypeptides toward clinical translation

The recent outbreaks of infectious diseases caused by multidrug-resistant pathogens have sounded a piercing alarm for the need of new effective antimicrobial agents to guard public health. Among different types of candidates, antimicrobial peptides (AMPs) and the synthetic mimics of AMPs (SMAMPs) have attracted significant enthusiasm in the past thirty years, due to their unique membrane-active antimicrobial mechanism and broad-spectrum antimicrobial activity. The extensive research has brought many drug candidates into clinical and pre-clinical development. Despite tremendous progresses have been made, several major challenges inherent to current design strategies have slowed down the clinical translational development of AMPs and SMAMPs. However, these challenges also triggered many efforts to redesign and repurpose AMPs. In this review, we will first give an overview on AMPs and their synthetic mimics, and then discuss the current status of their clinical translation. Finally, the recent advances in redesign and repurposing AMPs and SMAMPs are highlighted.

Synthesis and biological evaluation of stilbene-based peptoid mimics against the phytopathogenic bacterium Xanthomonas citri pv. citri

BACKGROUND

The emergence of drug-resistant phytopathogenic bacteria and the need for new types of biological disease-control agents have accelerated efforts toward searching for alternative candidates with a low propensity for resistance development. In this study, a new series of stilbene-based peptoid mimics were synthesized, and their biological activities were evaluated against citrus pathogenic bacteria in vitro and in vivo.

RESULTS

Antibacterial bioassay results showed that the dicationic peptoid mimics 9a and 9b displayed excellent bioactivity against Xanthomonas citri pv. citri, with the minimum inhibitory concentration values of 25 μM, which were superior to those of commercial copper biocides Delite (200 μM) and Kasumin Bordeaux (100 μM). In vivo bioassay further confirmed their control efficacy against plant bacterial diseases. In addition, the antibacterial mechanism of action elucidated their membrane-disruption effects resulting in the leakage of the bacterial membranes, which was similar to that of antimicrobial peptides. Moreover, the inhibition effect on biofilm formation of peptoid mimics has also been demonstrated.

CONCLUSION

Stilbene-based peptoid mimics synthesized in this study showed promising antibacterial activity with a potent membrane-disruptive mechanism. The results suggested that stilbene-based peptoid mimics have the potential as a candidate new type of bactericide for citrus disease protection.

First orally bioavailable prodrug of proteolysis targeting chimera (PROTAC) degrades cyclin-dependent kinases 2/4/6 in vivo

A growing number of reports suggested that the inhibitor targeting cyclin-dependent kinases (CDK) 2/4/6 can act as a more feasible chemotherapy strategy. In the present paper, a novel PROTAC molecule was developed based on the structure of Ribociclib's derivative. In malignant melanoma cells, the degrader can not only degrade CDK 2/4/6 simultaneously and effectively, but also remarkably induce cell cycle arrest and apoptosis of melanoma cells. Moreover, PROTAC molecules with CRBN ligands always have poor oral bioavailability. We developed the orally bioavailable prodrug for the first time. It would provide general solution for oral administration of the PROTAC molecules, derived from CRBN ligands, for animal test conveniently.

Annular oxygenation and rearrangement products of cryptotanshinone by biotransformation with marine-derived fungi Cochliobolus lunatus and Aspergillus terreus

Structural modification of natural products by biotransformation with fungi is an attractive tool to obtain novel bioactive derivatives. In the present study, cryptotanshinone (1), a quinoid abietane diterpene from traditional Chinese medicine Salvia miltiorrhiza (Danshen), was transformed by two marine-derived fungi. By using Cochliobolus lunatus TA26-46, one new oxygenated and rearranged product (2), containing a 5,6-dihydropyrano[4,3-b]chromene moiety, together with one known metabolite (10), were obtained from the converted broth of cryptotanshinone (1) with the isolated yields of 1.0% and 2.1%, respectively. While, under the action of Aspergillus terreus RA2905, seven new transformation products (3-9) as well as 10 with the fragments of 2-methylpropan-1-ol and oxygenated p-benzoquinone were produced and obtained with the isolated yields of 0.1%-1.3%. The structures of the new compounds were elucidated by comprehensive spectroscopic analysis including High Resolution Electrospray Ionization Mass Spectroscopy (HRESIMS), Nuclear Magnetic Resonance (NMR) and Electronic Circular Dichroism (ECD). The metabolic pathways of cryptotanshinone by these two fungi were presumed to be the opening and rearrangement of furan ring, and/or oxygenation of cyclohexane ring. Cryptotanshinone (1) and its metabolites displayed anti-inflammatory activities against NO production in LPS-stimulated BV-2 cells and antibacterial activities towards methicillin-resistant Staphylococcus aureus. These findings revealed the potential of marine fungi to transform the structures of natural products by biotransformation.

Aggregation-Induced Emissive and Circularly Polarized Homogeneous Sulfono-γ-AApeptide Foldamers

Through our continuous effort in developing a new class of foldamers, we have both designed and synthesized homogenous sulfono-γ-AApeptides using tetraphenylethylene (TPE) moieties attached to the backbone as luminogenic sidechains. Based on previous crystal structures, we have found that these foldamers adopted a left-handed 414-helix. Due to the constraint of the helical scaffold, the rotation of the TPE moieties were restricted, leading to fluorescent emissive properties with high quantum yields not only at the aggregate state but also in solution. Investigation of the relationship between the structure and fluorescence behavior reveals that emission was induced by the combined effect of the aggregation-induced emission (AIE) and the rotated restriction from the backbone. Furthermore, as the packing mode of the luminogens could be precisely adjusted by the helical backbone, these foldamers were found to be circularly polarizable with relatively large luminescence dissymmetry factor (g lum). Interestingly, possessing cationic amphipathic structures similar to that of host-defense peptides (HDPs), these sulfono-γ-AApeptides were able to inhibit the growth of Gram-positive bacteria methicillin-resistant S. aureus (MRSA) through membrane interactions.

Dimeric γ-AApeptides With Potent and Selective Antibacterial Activity

Over the past few decades, the emergence of antibiotic resistance developed by life-threatening bacteria has become increasingly prevalent. Thus, there is an urgent demand to develop novel antibiotics capable of mitigating this trend. Herein, we report a series of dimeric γ-AApeptide derivatives as potential antibiotic agents with limited toxicity and excellent selectivity against Gram-positive strains. Among them, compound 2 was identified to have the best MICs without inducing drug resistance, even after exposure to MRSA for 20 passages. Time-kill kinetics and mechanistic studies suggested that 2 could mimic host-defense peptides (HDPs) and rapidly eradicate MRSA within 2 hours through disturbing the bacteria membrane. Meanwhile, biofilm formation was successfully inhibited even at a low concentration. Taken together, these results suggested the great potential of dimeric γ-AApeptide derivatives as antibacterial agents.

Small Molecules with Membrane-Active Antibacterial Activity

This spotlight on application provides a brief overview of our research exploration, focusing on the research of small molecules with membrane-active antibacterial activity that mimic host-defense peptides (HDPs). The development of antimicrobial HDP agents is an emerging research area as they circumvent the potential disadvantages of HDPs. The small molecules are preferable for development due to their low production cost and potential of more practical applications. In recent years, we conducted research on the design of antibacterial agents based on small molecules including hydantoins, acylated reduced amides, biscyclic guanidines, and dimeric alkylamides of lysines. We herein sketch our journey on the exploration of the antimicrobial activity of these few classes of molecules and hopefully share our insight in the future design of small-molecular-weight antibiotic agents with membrane-active activity that mimic HDPs.

Hydrophobicity-Modulated Small Antibacterial Molecule Eradicates Biofilm with Potent Efficacy against Skin Infections

The role of molecular arrangement of hydrophobic and hydrophilic groups for designing membrane-active molecules remains largely ambiguous. To explore this aspect, herein we report a series of membrane-active small molecules by varying the spatial distribution of hydrophobic groups. The two terminal amino groups of linear triamines such as diethylene triamine, bis(trimethylene)triamine, and bis(hexamethylene)triamine were conjugated with cationic amino acids bearing variable side chain hydrophobicity (such as diaminobutyric acid, ornithine, and lysine). The hydrophobicity was also modulated through conjugation of different long chain fatty acids with the central secondary amino group of the triamine. Molecules with constant backbone hydrophobicity displayed an enhanced antibacterial activity and decreased hemolytic activity upon increasing the side chain hydrophobicity of amino acids. On the other hand, increased hydrophobicity in the backbone introduced a slight hemolytic activity but a higher increment in antibacterial activity, resulting in better selective antibacterial compounds. The optimized lead compound derived from structure-activity-relationship (SAR) studies was the dodecanoyl analogue of a lysine series of compounds consisting of bis(hexamethylene)triamine as the backbone. This compound was active against various Gram-positive and Gram-negative bacteria at a low concentration (MIC ranged between 3.1 and 6.3 μg/mL) and displayed low toxicity toward mammalian cells (HC₅₀ = 890 μg/mL and EC₅₀ against HEK = 85 μg/mL). Additionally, it was able to kill metabolically inactive bacterial cells and eradicate preformed biofilms of MRSA. This compound showed excellent activity in a mouse model of skin infection with reduction of ∼4 log MRSA burden at 40 mg/kg dose without any sign of skin toxicity even at 200 mg/kg. More importantly, it revealed potent efficacy in an ex vivo model of human skin infection (with reduction of 85% MRSA burden at 50 μg/mL), which indicates great potential of the compound as an antibacterial agent to treat skin infections.

Cu-catalyzed N-3-Arylation of Hydantoins Using Diaryliodonium Salts

A general Cu-catalyzed, regioselective method for the N-3-arylation of hydantoins is described. The protocol utilizes aryl(trimethoxyphenyl)iodonium tosylate as the arylating agent in the presence of triethylamine and a catalytic amount of a simple Cu-salt. The method is compatible with structurally diverse hydantoins and operates well with neutral aryl groups or aryl groups bearing weakly donating/withdrawing elements. It is also applicable for the rapid diversification of pharmaceutically relevant hydantoins.

Enzyme-Responsive Ag Nanoparticle Assemblies in Targeting Antibacterial against Methicillin-Resistant Staphylococcus Aureus

The abuse of antibiotics resulted in the emergence of antibiotics-resistant bacteria, which has raised a great social concern together with the impetus to develop effective antibacterial materials. Herein, the synthesis of biocompatible enzyme-responsive Ag nanoparticle assemblies (ANAs) and their application in the high-efficiency targeted antimicrobial treatment of methicillin-resistant Staphylococcus aureus (MRSA) have been demonstrated. The ANAs could collapse and undergo stable/collapsed transition on approaching MRSA because of the serine protease-like B enzyme proteins (SplB)-triggered decomposition of the branched copolymers which have been employed as the macrotemplate in the synthesis of responsive ANAs. This transition contributed greatly to the high targeting affinity and efficiency of ANAs to MRSA. The minimum inhibitory concentration and minimum bactericidal concentration against MRSA were 2.0 and 32.0 μg mL^-1, respectively. Skin wound healing experiments confirmed that the responsive ANAs could serve as an effective wound dressing to accelerate the healing of MRSA infection.