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

Rational design and synthesis of novel phenyltriazole derivatives targeting MRSA cell wall biosynthesis

Antimicrobial resistance in methicillin-resistant Staphylococcus aureus (MRSA) is a major global health challenge. This study reports the design and synthesis of novel phenyltriazole derivatives as potential anti-MRSA agents. The new scaffold replaces the thiazole core with a 1,2,3-triazole ring, enhancing antimicrobial efficacy and physicochemical properties. A series of derivatives were synthesized and evaluated, with four compounds (20, 23, 29 and 30) showing significant activity against MRSA (MIC ≤ 4 μg mL-1). Compound 29 emerged as the most promising candidate, showing rapid bactericidal activity and superior performance over vancomycin in time-kill assays. It exhibited selective toxicity against bacterial cells, minimal cytotoxicity in human cell lines and low hemolytic activity. Mechanistic studies showed that compound 29 targets the bacterial cell wall by binding to penicillin-binding protein 2a (PBP2a), disrupting cell wall integrity. Additionally, it showed strong anti-biofilm activity and reduced MRSA biofilms by up to 40%. Preliminary pharmacokinetic profiles suggested a favorable profile, including a prolonged plasma half-life and good oral bioavailability. These results suggest that compound 29 is a promising lead for further development in the fight against MRSA.

Machine Learning-Based Virtual Screening of Antibacterial Agents against Methicillin-Susceptible and Resistant Staphylococcus aureus

The application of computer-aided drug discovery (CADD) approaches has enabled the discovery of new antimicrobial therapeutic agents in the past. The high prevalence of methicillin-resistantStaphylococcus aureus(MRSA) strains promoted this pathogen to a high-priority pathogen for drug development. In this sense, modern CADD techniques can be valuable tools for the search for new antimicrobial agents. We employed a combination of a series of machine learning (ML) techniques to select and evaluate potential compounds with antibacterial activity against methicillin-susceptible S. aureus (MSSA) and MRSA strains. In the present study, we describe the antibacterial activity of six compounds against MSSA and MRSA reference (American Type Culture Collection (ATCC)) strains as well as two clinical strains of MRSA. These compounds showed minimal inhibitory concentrations (MIC) in the range from 12.5 to 200 μM against the different bacterial strains evaluated. Our results constitute relevant proven ML-workflow models to distinctively screen for novel MRSA antibiotics.

New Phenylthiazoles: Design, Synthesis, and Biological Evaluation as Antibacterial, Antifungal, and Anti-COVID-19 Candidates

The combination of antibacterial and antiviral agents is becoming a very important aspect of dealing with resistant bacterial and viral infections. The N-phenylthiazole scaffold was found to possess significant anti-MRSA, antifungal, and anti-COVID-19 activities as previously published; hence, a slight refinement was proposed to attach various alkyne lipophilic tails to this promising scaffold, to investigate their effects on the antimicrobial activity of the newly synthesized compounds and to provide a valuable structure-activity relationship. Phenylthiazole 4 m exhibited the most potent anti-MRSA activity with 8 μg/mL MIC value. Compounds 4 k and 4 m demonstrated potent activity against Clostridium difficile with MIC values of 2 μg/mL and moderate activity against Candida albicans with MIC value of 4 μg/mL. When analyzed for their anti-COVID-19 inhibitory effect, compound 4 b emerged with IC50 =1269 nM and the highest selectivity of 138.86 and this was supported by its binding score of -5.21 kcal mol-1 when docked against SARS-CoV-2 M pro . Two H-bonds were formed, one with His164 and the other with Met49 stabilizing phenylthiazole derivative 4 b, inside the binding pocket. Additionally, it created two arene-H bonds with Asn142 and Glu166, through the phenylthiazole scaffold and one arene-H bond with Leu141 via the phenyl ring of the lipophilic tail.

Alanine racemase a promising Helicobacter pylori drug target inhibited by propanoic acid

Eradication of Helicobacter pylori, the class 1 carcinogen, faces several obstacles, which demand alternative options to conventional drug development methods. Alanine racemase (Alr) was proposed as H. pylori drug target, inhibited by propanoic acid (PA), in a previous in silico study. We investigated the possible treatment of H. pylori infection through Alr inhibition. A new model of H. pylori Alr was built, validated, and the binding of PA to the active site was modelled via molecular docking with a good docking score. PA minimum inhibitory concentration (MIC) against H. pylori ATCC 43504 and six H. pylori clinical isolates ranged from 312.5 to 416.7 ± 180 μg/ml and remained unchanged after 14 serial passages in increasing PA concentrations. The minimum bactericidal concentration of PA was 625 μg/ml. Selective Alr inhibition was confirmed by a significant PA MIC increase with increasing d-alanine concentrations. Similar PA MIC in other tested pathogens was recorded (312.5-625 μg/ml). PA lacked cytotoxicity in tested cell lines and efficiently eradicated H. pylori in a rat infection model. In conclusion, Alr is a promising broad-spectrum drug target, inhibited by PA without resistance development by repeated exposure for 14 serial passages.

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.

Synthesis and Development of N-2,5-Dimethylphenylthioureido Acid Derivatives as Scaffolds for New Antimicrobial Candidates Targeting Multidrug-Resistant Gram-Positive Pathogens

The growing antimicrobial resistance to last-line antimicrobials among Gram-positive pathogens remains a major healthcare emergency worldwide. Therefore, the search for new small molecules targeting multidrug-resistant pathogens remains of great importance. In this paper, we report the synthesis and in vitro antimicrobial activity characterisation of novel thiazole derivatives using representative Gram-negative and Gram-positive strains, including tedizolid/linezolid-resistant S. aureus, as well as emerging fungal pathogens. The 4-substituted thiazoles 3h, and 3j with naphthoquinone-fused thiazole derivative 7 with excellent activity against methicillin and tedizolid/linezolid-resistant S. aureus. Moreover, compounds 3h, 3j and 7 showed favourable activity against vancomycin-resistant E. faecium. Compounds 9f and 14f showed broad-spectrum antifungal activity against drug-resistant Candida strains, while ester 8f showed good activity against Candida auris which was greater than fluconazole. Collectively, these data demonstrate that N-2,5-dimethylphenylthioureido acid derivatives could be further explored as novel scaffolds for the development of antimicrobial candidates targeting Gram-positive bacteria and drug-resistant pathogenic fungi.

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.

Aspartate α-decarboxylase a new therapeutic target in the fight against Helicobacter pylori infection

Effective eradication therapy for Helicobacter pylori is a worldwide demand. Aspartate α-decarboxylase (ADC) was reported as a drug target in H. pylori, in an in silico study, with malonic acid (MA) as its inhibitor. We evaluated eradicating H. pylori infection through ADC inhibition and the possibility of resistance development. MA binding to ADC was modeled via molecular docking. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of MA were determined against H. pylori ATCC 43504, and a clinical H. pylori isolate. To confirm selective ADC inhibition, we redetermined the MIC in the presence of products of the inhibited enzymatic pathway: β-alanine and pantothenate. HPLC was used to assay the enzymatic activity of H. pylori 6x-his tagged ADC in the presence of different MA concentrations. H. pylori strains were serially exposed to MA for 14 passages, and the MICs were determined. Cytotoxicity in different cell lines was tested. The efficiency of ADC inhibition in treating H. pylori infections was evaluated using a Sprague–Dawley (SD) rat infection model. MA spectrum of activity was determined in different pathogens. MA binds to H. pylori ADC active site with a good docking score. The MIC of MA against H. pylori ranged from 0.5 to 0.75 mg/mL with MBC of 1.5 mg/mL. Increasing β-alanine and pantothenate concentrations proportionally increased MA MIC. The 6x-his tagged ADC activity decreased by increasing MA concentration. No resistance to ADC inhibition was recorded after 14 passages; MA lacked cytotoxicity in all tested cell lines. ADC inhibition effectively eradicated H. pylori infection in SD rats. MA had MIC between 0.625 to 1.25 mg/mL against the tested bacterial pathogens. In conclusion, ADC is a promising target for effectively eradicating H. pylori infection that is not affected by resistance development, besides being of broad-spectrum presence in different pathogens. MA provides a lead molecule for the development of an anti-helicobacter ADC inhibitor. This provides hope for saving the lives of those at high risk of infection with the carcinogenic H. pylori.

Isoquinoline Antimicrobial Agent: Activity against Intracellular Bacteria and Effect on Global Bacterial Proteome

A new class of alkynyl isoquinoline antibacterial compounds, synthesized via Sonogashira coupling, with strong bactericidal activity against a plethora of Gram-positive bacteria including methicillin- and vancomycin-resistant Staphylococcus aureus (S. aureus) strains is presented. HSN584 and HSN739, representative compounds in this class, reduce methicillin-resistant S. aureus (MRSA) load in macrophages, whilst vancomycin, a drug of choice for MRSA infections, was unable to clear intracellular MRSA. Additionally, both HSN584 and HSN739 exhibited a low propensity to develop resistance. We utilized comparative global proteomics and macromolecule biosynthesis assays to gain insight into the alkynyl isoquinoline mechanism of action. Our preliminary data show that HSN584 perturb S. aureus cell wall and nucleic acid biosynthesis. The alkynyl isoquinoline moiety is a new scaffold for the development of potent antibacterial agents against fatal multidrug-resistant Gram-positive bacteria.

Mechanistic Studies and In Vivo Efficacy of an Oxadiazole-Containing Antibiotic

Methicillin-resistant Staphylococcus aureus (MRSA) infections are still difficult to treat, despite the availability of many FDA-approved antibiotics. Thus, new compound scaffolds are still needed to treat MRSA. The oxadiazole-containing compound, HSGN-94, has been shown to reduce lipoteichoic acid (LTA) in S. aureus, but the mechanism that accounts for LTA biosynthesis inhibition remains uncharacterized. Herein, we report the elucidation of the mechanism by which HSGN-94 inhibits LTA biosynthesis via utilization of global proteomics, activity-based protein profiling, and lipid analysis via multiple reaction monitoring (MRM). Our data suggest that HSGN-94 inhibits LTA biosynthesis via direct binding to PgcA and downregulation of PgsA. We further show that HSGN-94 reduces the MRSA load in skin infection (mouse) and decreases pro-inflammatory cytokines in MRSA-infected wounds. Collectively, HSGN-94 merits further consideration as a potential drug for staphylococcal infections.

Cascade synthetic strategies opening access to medicinal-relevant aliphatic 3- and 4-membered N-heterocyclic scaffolds

Cascade reactions are often 'employed' by nature to construct structurally diverse nitrogen-containing heterocycles in a highly stereoselective fashion, i.e., secondary metabolites important for pharmacy. Nitrogen-containing heterocycles of three- and four-membered rings, as standalone and bicyclic compounds, inhibit different enzymes and are pharmacophores of approved drugs or drug candidates considered in many therapies, e.g. anticancer, antibacterial or antiviral. Domino transformations are in most cases in line with modern green chemistry concepts due to atom economy, one-pot procedures often without use the protective groups, time-saving and at markedly lower costs than multistep transformations. The tandem approaches can help to obtain novel N-heterocyclic scaffolds, functionalized according to structural requirements of the target in cells, taking into account the nature of functional group and stereochemistry. On the other hand cascade strategies allow to modify small N-heterocyclic rings in a systematic way, which is beneficial for structure-activity relationship (SAR) analyses. This review is focused on the biological relevance of the N-heterocyclic scaffolds with smaller 3- and 4-membered rings among approved drugs and leading structures of drug candidates. The cascade synthetic strategies offering N-heterocyclic scaffolds, at relatively good yields and high stereoselectivity, are discussed here. The review covers mainly years from 2015 to 2021.

In Silico Resources of Drug-Likeness as a Mirror: What Are We Lacking in Pesticide-Likeness?

Unfavorable bioavailability is an important aspect underlying the failure of drug candidates. Computational approaches for evaluating drug-likeness can minimize these risks. Over the past decades, computational approaches for evaluating drug-likeness have sped up the process of drug development and were also quickly derived to pesticide-likeness. As a result of many critical differences between drugs and pesticides, many kinds of methods for drug-likeness cannot be used for pesticide-likeness. Therefore, it is crucial to comprehensively compare and analyze the differences between drug-likeness and pesticide-likeness, which may provide a basis for solving the problems encountered during the evaluation of pesticide-likeness. Here, we systematically collected the recent advances of drug-likeness and pesticide-likeness and compared their characteristics. We also evaluated the current lack of studies on pesticide-likeness, the molecular descriptors and parameters adopted, the pesticide-likeness model on pesticide target organisms, and comprehensive analysis tools. This work may guide researchers to use appropriate methods for developing pesticide-likeness models. It may also aid non-specialists to understand some important concepts in drug-likeness and pesticide-likeness.

Synthesis and biological evaluation of novel withangulatin A derivatives as potential anticancer agents

Novel withangulatin A (WA) derivatives were synthesized and evaluated for antiproliferative activity against four human cancer cell lines (U2OS, MDA-MB-231, HepG2, and A549). Among these derivatives, 10 exhibited the most potent antiproliferative activity, with an IC₅₀ value of 74.0 nM against the human breast cancer cell line MDA-MB-231 and potency that was 70-fold that of WA (IC₅₀ = 5.22 µM). Moreover, 10 caused G2-phase cell cycle arrest in a concentration-dependent manner and induced the apoptosis of MDA-MB-231 cells by increasing intracellular reactive oxygen species (ROS). Compound 10 showed a high selectivity index (SI = 267.03) for breast cancer MDA-MB-231 cells. These results suggest that 10 is a promising anticancer agent.

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.

Regio- and Diastereoselective Synthesis of 2-Arylazetidines: Quantum Chemical Explanation of Baldwin's Rules for the Ring-Formation Reactions of Oxiranes†

A general, scalable two-step regio- and diastereoselective method has been described for the synthesis of versatile alkaloid-type azetidines from simple building blocks with excellent overall yields. In the kinetically controlled reaction, only the formation of the strained four-membered ring can be achieved instead of the thermodynamically favorable five-membered rings under appropriate conditions. Remarkable functional group tolerance has also been demonstrated. In this paper, we give a new scope of Baldwin’s rules by density functional theory (DFT) calculations with an explicit solvent model, confirming the proposed reaction mechanisms and the role of kinetic controls in the stereochemical outcome of the reported transition-metal-free carbon–carbon bond formation reactions.

β,γ-Diaryl α-methylene-γ-butyrolactones as potent antibacterials against methicillin-resistant Staphylococcus aureus

A selected series of racemic α-methylene-γ-butyrolactones (AMGBL) synthesized via allylboration or allylindation reactions were screened against methicillin-resistant Staphylococcus aureus (MRSA) USA300. Unlike natural AMGBLs, such as parthenolide, synthetic analogs bearing aryl moieties at the β- and γ-positions are potent against MRSA. The most potent molecules were comparable to vancomycin and linezolid, the drugs of the last resort for MRSA infections, in their effectiveness with minimum inhibitory concentrations (MICs) ranging from 3.0 to 5.2 μM. These lactones also exhibited potent antibacterial activity against other clinically important multidrug-resistant Gram-positive bacteria (except enterococci), while also showing high tolerability to mammalian cells. Several of these molecules surpassed vancomycin in their rapid killing of the high MRSA inoculum (2 h vs 12 h) in a standard time-kill kinetics assay, with compounds 1l and 1m significantly reducing the intracellular burden of MRSA by about 98-99%, at low concentrations. Additionally, the compounds surpassed vancomycin in inhibiting staphylococcal protease production, indicating that synthetic methylene lactones warrant further investigations as promising anti-MRSA candidates.

Evaluation of N-phenyl-2-aminothiazoles for treatment of multi-drug resistant and intracellular Staphylococcus aureus infections

The increasing emergence of antibiotic-resistant bacterial pathogens calls for additional urgency in the development of new antibacterial candidates. N-Phenyl-2-aminothiazoles are promising candidates that possess potent anti-MRSA activity and could potentially replenish the MRSA antibiotic pipeline. The initial screen of a series of compounds in this novel class against several bacterial strains revealed that the aminoguanidine analogues possessed promising activities and superior safety profiles. The determined MICs of these compounds were comparable to, if not better than, those of the control drugs (linezolid and vancomycin). Remarkably, compounds 3a, 3b, and 3e possessed potent activities against multidrug resistant staphylococcal isolates and several clinically important pathogens, such as vancomycin-resistant enterococci (VRE) and Streptococcus pneumoniae. In addition, the compounds were superior to vancomycin in the rapid killing of MRSA and the longer post-antibiotic effects. Furthermore, low concentrations of compounds 3a, 3b, and 3e reduced the intracellular burden of MRSA by greater than 90%. Initial in vitro PK/toxicity assessments revealed that compound 3e was highly tolerable and possessed a low metabolic clearance rate and a highly acceptable half-life.