Design and synthesis of thiazole derivatives as potent FabH inhibitors with antibacterial activity

Lipid-Centric Approaches in Combating Infectious Diseases: Antibacterials, Antifungals and Antivirals with Lipid-Associated Mechanisms of Action

One of the global challenges of the 21st century is the increase in mortality from infectious diseases against the backdrop of the spread of antibiotic-resistant pathogenic microorganisms. In this regard, it is worth targeting antibacterials towards the membranes of pathogens that are quite conservative and not amenable to elimination. This review is an attempt to critically analyze the possibilities of targeting antimicrobial agents towards enzymes involved in pathogen lipid biosynthesis or towards bacterial, fungal, and viral lipid membranes, to increase the permeability via pore formation and to modulate the membranes' properties in a manner that makes them incompatible with the pathogen's life cycle. This review discusses the advantages and disadvantages of each approach in the search for highly effective but nontoxic antimicrobial agents. Examples of compounds with a proven molecular mechanism of action are presented, and the types of the most promising pharmacophores for further research and the improvement of the characteristics of antibiotics are discussed. The strategies that pathogens use for survival in terms of modulating the lipid composition and physical properties of the membrane, achieving a balance between resistance to antibiotics and the ability to facilitate all necessary transport and signaling processes, are also considered.

Improving Antimicrobial Activity and Physico-Chemical Properties by Isosteric Replacement of 2-Aminothiazole with 2-Aminooxazole

Antimicrobial drug resistance is currently one of the most critical health issues. Pathogens resistant to last-resort antibiotics are increasing, and very few effective antibacterial agents have been introduced in recent years. The promising drug candidates are often discontinued in the primary stages of the drug discovery pipeline due to their unspecific reactivity (PAINS), toxicity, insufficient stability, or low water solubility. In this work, we investigated a series of substituted N-oxazolyl- and N-thiazolylcarboxamides of various pyridinecarboxylic acids. Final compounds were tested against several microbial species. In general, oxazole-containing compounds showed high activity against mycobacteria, especially Mycobacterium tuberculosis (best MIC_H37Ra = 3.13 µg/mL), including the multidrug-resistant strains. Promising activities against various bacterial and fungal strains were also observed. None of the compounds was significantly cytotoxic against the HepG2 cell line. Experimental measurement of lipophilicity parameter log k’_w and water solubility (log S) confirmed significantly (typically two orders in logarithmic scale) increased hydrophilicity/water solubility of oxazole derivatives in comparison with their thiazole isosteres. Mycobacterial β-ketoacyl-acyl carrier protein synthase III (FabH) was suggested as a probable target by molecular docking and molecular dynamics simulations.

Inhibitors of aminoacyl-tRNA synthetases as antimycobacterial compounds: An up-to-date review

Aminoacyl-tRNA synthetases (aaRSs) are crucial for the correct assembly of amino acids to cognate tRNA to maintain the fidelity of proteosynthesis. AaRSs have become a hot target in antimicrobial research. Three aaRS inhibitors are already in clinical practice; antibacterial mupirocin inhibits the synthetic site of isoleucyl-tRNA synthetase, antifungal tavaborole inhibits the editing site of leucyl-tRNA synthetase, and antiprotozoal halofuginone inhibits proline-tRNA synthetase. According to the World Health Organization, tuberculosis globally remains the leading cause of death from a single infectious agent. The rising incidence of multidrug-resistant tuberculosis is alarming and urges the search for new antimycobacterial compounds, preferably with yet unexploited mechanism of action. In this literature review, we have covered the up-to-date state in the field of inhibitors of mycobacterial aaRSs. The most studied aaRS in mycobacteria is LeuRS with at least four structural types of inhibitors, followed by TyrRS and AspRS. Inhibitors of MetRS, LysRS, and PheRS were addressed in a single significant study each. In many cases, the enzyme inhibition activity translated into micromolar or submicromolar inhibition of growth of mycobacteria. The most promising aaRS inhibitor as an antimycobacterial compound is GSK656 (compound 8), the only aaRS inhibitor in clinical trials (Phase IIa) for systemic use against tuberculosis. GSK656 is orally available and shares the oxaborole tRNA-trapping mechanism of action with antifungal tavaborole.

Discovery of Natural FabH Inhibitors Using an Immobilized Enzyme Column and Their Antibacterial Activity against Xanthomonas oryzae pv. oryzae

β-Ketoacyl-acyl carrier protein synthase III (KAS III, FabH) is essential for bacterial fatty acid biosynthesis. Recent studies indicate that FabH can be a potential target for bactericide development. In the present study, an immobilized FabH column was developed and used to screen FabH inhibitors from complex natural product extracts. Combined with HPLC, four secondary metabolites, alternariol (1), altenuisol (2), alterlactone (3), and dehydroaltenusin (4), were site-directed, isolated, and identified from the crude extract of Alternaria alternata ZHJG5. These compounds showed inhibitory activities on FabH of Xanthomonas oryzae pv. oryzae (Xoo) with IC50 values from 29.5 to 74.1 μM and also displayed a varying degree of antibacterial activities against Xoo with minimal inhibitory concentration values from 4 to 64 μg/mL. Molecular modeling was then used to picture how the compounds interact with XooFabH. Two inhibitors, compounds 1 and 3, exhibited significant bactericidal activity against rice bacterial leaf blight with a protective efficiency of 66.2 and 82.5% at the concentration of 200 μg/mL, respectively, suggesting that they could be lead candidates to develop novel bactericides.

Design, Synthesis, Docking and Computational Pharmacokinetic Profiling of New Pyrazolinyl Thiazolinone Biheterocycles as Potent Antimicrobial Agents

Background:

Development of potential antimicrobial agents is the main aim in the drug discovery process to overcome the problem of drug resistance. Pyrazolines and thiazolinones are extensively used as building blocks for the synthesis of diverse and medicinally important compounds.

Methods:

In this present work, a new series of functionalized pyrazolinyl-thiazolinone biheterocycles is designed and synthesized from N-pyrazolinecarbothioamide. Antimicrobial screening is carried out in order to discover their potential towards six bacterial and four fungal strains. The zone of inhibition (ZI in mm) was determined by the disc diffusion method and minimum inhibitory concentration (MIC in μg/mL) by macro dilution method. The druggability of these new entities is done through in silico pharmacokinetic profiling using Maestro 2017-1 interface of Schrӧdinger software.

Results and Disscusion:

Compounds 4c and 4e with chloro and iodo substituents on Nphenylacetamide ring displayed good inhibitory antibacterial activity against the tested bacterial strains with minimum MIC values when compared to the reference drug tetracycline. Compound 3 with an acetic acid derivative showed high antifungal activity among all the tested derivatives. Compound 3 not only showed antifungal activity but also qualified druggability test with no violation of Lipinski rule of five.

Conclusion:

The capability of the synthesized pyrazolinyl-thiazolinone derivatives was performed to efficiently inhibit the growth of microorganisms against selected bacterial and fungal strains. Further, these compounds are found to be effectively bound to the active sites of attractive target Escherichia coli FabH.

Synthesis, Molecular Docking, DFT Study of Novel N-Benzyl-2-(3-cyano-4-isobutoxyphenyl)- 4-methylthiazole-5-carboxamide Derivatives and their Antibacterial Activity

A series of febuxostat based new chemical entities was synthesized using microwave method and characterized by NMR, mass and FT-IR spectral studies. Molecular docking of febuxostat amide nucleus substitution compounds 8c (-7.91kcal/mol), 8g (-7.94 kcal/mol) exhibiting high binding energy against ALK receptors. Theoretical investigation of MEPs, HOMO, LUMO and energy gap of HOMO-LUMO were calculated by B3LYP/6-31G method. Among the tested compounds, methoxy substituted compound 8g showed highest antibacterial activity against S. aereus and B. subtilis.

Design, synthesis and biological evaluation of novel β-pinene-based thiazole derivatives as potential anticancer agents via mitochondrial-mediated apoptosis pathway

A series of novel β-pinene-based thiazole derivatives were synthesized and characterized by HRMS, ¹H NMR, and ¹³C NMR analyses as potential antineoplastic agents. Derivatives were evaluated for their anticancer activities in vitro, and the data manifested that most target compounds showed potent anti-proliferative activities against three human cancer cell lines. Especially, compound 5g displayed excellent cytotoxic activity against Hela, CT-26, and SMMC-7721 cell lines with IC₅₀ values of 3.48 ± 0.14, 8.84 ± 0.16, and 6.69 ± 0.15 µM, respectively. To determine the underlying mechanism of compound 5g on cell viability, DAPI staining, Annexin-V/PI staining, JC-1 staining, DCFDA staining, and Western blot analysis were performed. Our data showed that compound 5g inhibited cell proliferation by inducing apoptosis and cell cycle arrest of Hela cells at the G0/G1 phase in a dose dependent manner. Further studies revealed that compound 5g enhanced levels of reactive oxygen species (ROS), caused a decrease in mitochondrial membrane potential, increased the release of mitochondrial cytochrome C, and affected the expression of Bax, Bcl-2, caspase-3 and caspase-9. Thus, our findings indicated that compound 5g induced apoptosis in Hela through ROS-mediated mitochondrial dysfunction signaling pathways.

Structure and substrate specificity of β-ketoacyl-acyl carrier protein synthase III from Acinetobacter baumannii

Originally annotated as the initiator of fatty acid synthesis (FAS), β-ketoacyl-acyl carrier protein synthase III (KAS III) is a unique component of the bacterial FAS system. Novel variants of KAS III have been identified that promote the de novo use of additional extracellular fatty acids by FAS. These KAS III variants prefer longer acyl-groups, notably octanoyl-CoA. Acinetobacter baumannii, a clinically important nosocomial pathogen, contains such a multifunctional KAS III (AbKAS III). To characterize the structural basis of its substrate specificity, we determined the crystal structures of AbKAS III in the presence of different substrates. The acyl-group binding cavity of AbKAS III and co-crystal structure of AbKAS III and octanoyl-CoA confirmed that the cavity can accommodate acyl groups with longer alkyl chains. Interestingly, Cys264 formed a disulfide bond with residual CoA used in the crystallization, which distorted helices at the putative interface with acyl-carrier proteins. The crystal structure of KAS III in the alternate conformation can also be utilized for designing novel antibiotics.

Design, synthesis and antimycobacterial activity of hybrid molecules combining pyrazinamide with a 4-phenylthiazol-2-amine scaffold

Hybrid compounds based on a combination of the first-line antitubercular pyrazinamide (PZA) and a formerly identified antimycobacterial scaffold of 4-arylthiazol-2-amine were designed. Eighteen compounds were prepared, characterized and tested for in vitro growth inhibition activity against M. tuberculosis H37Rv, M. kansasii, M. avium and M. smegmatis by Microplate Alamar Blue Assay at neutral pH. Active compounds were tested for in vitro cytotoxicity in the human hepatocellular carcinoma cell line (HepG2). The most active 6-chloro-N-[4-(4-fluorophenyl)thiazol-2-yl]pyrazine-2-carboxamide (9b) also had the broadest spectrum of activity and inhibited M. tuberculosis, M. kansasii, and M. avium with MIC = 0.78 μg mL^-1 (2.3 μM) and a selectivity index related to HepG2 cells of SI > 20. Structure-activity relationships within the series are discussed. Based on its structural similarity to known inhibitors and the results of a molecular docking study, we suggest mycobacterial beta-ketoacyl-(acyl-carrier-protein) synthase III (FabH) as a potential target.

Mechanochemical solid-state synthesis of 2-aminothiazoles, quinoxalines and benzoylbenzofurans from ketones by one-pot sequential acid- and base-mediated reactions

α-Chloroketones - obtained by the atom-economical chlorination of ketones with trichloroisocyanuric acid (TCCA) in the presence of p-TSA under ball-milling conditions - were set up for a sequential base-mediated condensation reaction with thiourea/thiosemicarbazides, o-phenylenediamine and salicylaldehyde to afford 2-aminothiazoles, 2-hydrazinylthiazoles, quinoxalines and benzoylbenzofurans, respectively, in respectable yields. The viability of one-pot sequential acid- and base-mediated reactions in the solid state under ball-milling conditions is thus demonstrated.

Copper-catalyzed synthesis of thiazol-2-yl ethers from oxime acetates and xanthates under redox-neutral conditions

A copper-catalyzed [3+2] annulation of oxime acetates and xanthates to generate thiazol-2-yl ethers with good regioselectivity under redox-neutral conditions has been developed.

Access to Fully Substituted Thiazoles and 2,3-Dihydrothiazoles via Copper-Catalyzed [4 + 1] Heterocyclization of α-(N-Hydroxy/aryl)imino-β-oxodithioesters with α-Diazocarbonyls

An efficient chemoselective practical route to fully substituted thiazoles and 2,3-dihydrothiazoles has been devised by [4 + 1] heterocyclization of α-(N-hydroxy/aryl)imino-β-oxodithioesters with in situ generated Cu-carbenoids of diazocarbonyls. The α-(N-hydroxy/aryl)imino-β-oxodithioesters are readily accessible by the reaction of β-oxodithioesters with nitrous acid/nitrosoarenes. The overall transformation involves sequential N-O/C-N bonds cleavage followed by cascade C-N/C-S bonds formation in one-pot. This new strategy allows full control over the introduction of various sensitive functional groups at different positions of the thiazole ring, broadening the arsenal of synthetic methods to obtain such scaffolds.

Design and synthesis of 4,5-diaryl/heteroarylthiophene-2-carboxylic acid derivatives and evaluation of their biological activities

Synthesis, characterization and biological activity of novel 4,5-diaryl/heteroaryl thiophene-2-carboxylic acid derivatives are described. Aryl/heteroaryl esters were converted to substituted thiophene esters via a Vilsmeier-Haack reaction, which were then hydrolyzed to 4,5-diaryl/heteroaryl thiophene-2-carboxylic acid derivatives

Identification of novel 2-aminothiazole conjugated nitrofuran as antitubercular and antibacterial agents

The emergence of antibiotic resistant pathogens is an ongoing main problem in the therapy of bacterial infections. In order to develop promising antitubercular and antibacterial lead compounds, we designed and synthesized a new series of derivatives of 2-aminothiazole conjugated nitrofuran with activities against both Mycobacterium tuberculosis and Staphylococcus aureus. Eight compounds 12e, 12k, 12l, 12m, 18a, 18d, 18e, and 18j emerged as promising antitubercular agents. Structure-activity relationships (SARs) were discussed and showed that the derivatives substituted at the position-3 of benzene of 5-nitro-N-(4-phenylthiazol-2-yl)furan-2-carboxamide exhibited superior potency. The most potent compound 18e, substituted with benzamide at this position, displayed minimum inhibitory concentrations (MICs) of 0.27μg/mL against Mtb H37Ra and 1.36μg/mL against S. aureus. Furthermore, compound 18e had no obvious cytotoxicity to normal Vero cells (IC50=50.2μM). The results suggest that the novel scaffolds of aminothiazole conjugated nitrofuran would be a promising class of potent antitubercular and antimicrobial agents.