6,7-dihydroxyflavone dramatically intensifies the susceptibility of methicillin-resistant or -sensitive Staphylococcus aureus to beta-lactams

Chalcone derivatives and their antibacterial activities: Current development

The increase in antibiotic resistance due to various factors has encouraged the look for novel compounds which are active against multidrug-resistant pathogens. In this framework, chalcone-based compounds showed a diversity of pharmacological properties, and its derivatives possess a high degree of structural diversity, and it is helpful for the discovery of new therapeutic agents. The growing resistance to antibiotics worldwide has endangered their efficacy. This has led to a surging interest in the discovery of new antibacterial agents. Thus, there is an urgent need for new antibacterial drug candidates with increased strength, new targets, low cost, superior pharmacokinetic properties, and minimum side effects. The present review concluded and focuses on the recent developments in the area of medicinal chemistry to explore the diverse chemical structures of potent antibacterial agents and also describes its structure-activity relationships studies. The various synthetic structures leading to this class of neutral protective compound is common and additional structural optimization is promising for potential drug discovery and development.

Heterocyclization of polarized system: synthesis, antioxidant and anti-inflammatory 4-(pyridin-3-yl)-6-(thiophen-2-yl) pyrimidine-2-thiol derivatives

Background

Chalcones are intent in the daily diet as a favorable chemotherapeutic compound; on the other hand thiophene moiety is present in a large number of bioactive molecules having diverse biological efficiency.

Results

Our current goal is the synthesis of (E)-1-(pyridin-3-yl)-3-(thiophen-2-yl) prop-2-en-1-one 3 that^’s used as a starting compound to synthesize the novel pyrimidine-2-thiol, pyrazole, pyran derivatives. Chalcones 3 was prepared by condensation of 3-acetylpyridine with thiophene 2-carboxaldehyde which reacted with thiourea to obtain pyrimidinthiol derivative 4. Compound 4 was allowed to react with hydrazine hydrate to afford 2-hydrazinylpyrimidine derivative 5. Compound 5 was used as a key intermediate for a facile synthesis of the targets 6 and 7. In contrast, pyranone 8 was obtained by transformation of compound 5. Using as a precursor for the synthesis of new pyrazolo pyrimidine derivatives 9–10. The major incentive behind the preparation of these compounds was the immense biological activities associated to these heterocyclic derivatives.

Conclusions

The newly synthesized compounds (1–4) showed potent anti-inflammatory activities both in vitro and in vivo. They also exhibited promising antioxidant vitalities against α, α-diphenyl-β-picrylhydrazyl scavenging activity and lipid peroxidation. In conclusion, compound 1 showed a hopefully anti-inflammatory and antioxidant activities.

Flavonoids Suppress Pseudomonas aeruginosa Virulence through Allosteric Inhibition of Quorum-sensing Receptors

Quorum sensing is a process of cell-cell communication that bacteria use to regulate collective behaviors. Quorum sensing depends on the production, detection, and group-wide response to extracellular signal molecules called autoinducers. In many bacterial species, quorum sensing controls virulence factor production. Thus, disrupting quorum sensing is considered a promising strategy to combat bacterial pathogenicity. Several members of a family of naturally produced plant metabolites called flavonoids inhibit Pseudomonas aeruginosa biofilm formation by an unknown mechanism. Here, we explore this family of molecules further, and we demonstrate that flavonoids specifically inhibit quorum sensing via antagonism of the autoinducer-binding receptors, LasR and RhlR. Structure-activity relationship analyses demonstrate that the presence of two hydroxyl moieties in the flavone A-ring backbone are essential for potent inhibition of LasR/RhlR. Biochemical analyses reveal that the flavonoids function non-competitively to prevent LasR/RhlR DNA binding. Administration of the flavonoids to P. aeruginosa alters transcription of quorum sensing-controlled target promoters and suppresses virulence factor production, confirming their potential as anti-infectives that do not function by traditional bacteriocidal or bacteriostatic mechanisms.

Synthesis and Selective Cytotoxic Activities on Rhabdomyosarcoma and Noncancerous Cells of Some Heterocyclic Chalcones

Chemically diverse heterocyclic chalcones were prepared and evaluated for cytotoxicity, aiming to push forward potency and selectivity. They were tested against rhabdomyosarcoma (RMS) and noncancerous cell line (LLC-PK1). The influence of heteroaryl patterns on rings A and B was studied. Heterocycle functionalities on both rings, such as phenothiazine, thiophene, furan and pyridine were evaluated. Notably, the introduction of three methoxy groups at positions 3, 4, 5 on ring B appears to be critical for cytotoxicity. The best compound, with potent and selective cytotoxicity (IC₅₀ = 12.51 μM in comparison with the value 10.84 μM of paclitaxel), contains a phenothiazine moiety on ring A and a thiophene heterocycle on ring B. Most of the potential compounds only show weak cytoxicity on the noncancerous cell line LLC-PK1.

Galloylated flavonol rhamnosides from the leaves of Calliandra tergemina with antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA)

Galloylated flavonol rhamnosides identified as kaempferol-3-O-(2″,3″,4″-tri-O-galloyl)-α-l-rhamnopyranoside, quercetin-3-O-(3″,4″-di-O-galloyl)-α-l-rhamnopyranoside, and quercetin-3-O-(2″,3″,4″-tri-O-galloyl)-α-l-rhamnopyranoside, together with five known galloylated and non-galloylated flavonol rhamnosides, were isolated from leaves of Calliandra tergemina (L.) Benth. Their structures were established using spectroscopic methods and their antibacterial activities against methicillin-resistant Staphylococcus aureus (MRSA) were evaluated by a microdilution method.

Chemical composition and evaluation of modulatory of the antibiotic activity from extract and essential oil of Myracrodruon urundeuva

CONTEXT

The combination of antibiotics with natural products has demonstrated promising synergistic effects in several therapeutic studies.

OBJECTIVE

The aim of this study was to determine the effect of a combination of an ethanol extract of Myracrodruon urundeuva Fr. All. (Anacardiaceae) (aroeira plant) and its essential oil with six antimicrobial drugs against multiresistant strains of Staphylococcus aureus and Escherichia coli from clinical isolates.

MATERIALS AND METHODS

After identification of the chemical components by GC-MS, the antibacterial activity of the natural products and antibiotics was assessed by determining the minimal inhibitory concentration (MIC) using the microdilution method and concentrations ranging 8-512 μg/mL and 0.0012-2.5 mg/mL, respectively. Assays were performed to test for a possible synergistic action between the plant products and the antimicrobials, using the extract and the oil at a sub-inhibitory concentration (128 μg/mL) and antibiotic at concentrations varying between 8 and 512 μg/mL.

RESULTS

The GC-MS analysis identified the main compound as δ-carene (80.41%). The MIC of the natural products was >1024 μg/mL, except against S. aureus ATCC25923. Only the combinations of the natural products with gentamicin, amikacin and clindamycin were effective against S. aureus 358, enhancing the antibiotic activity by reducing the MIC.

CONCLUSIONS

The extract from aroeira showed a higher antibacterial activity and the oil was more effective in potentiating the activity of conventional antibiotics.

Synthesis and antibacterial activity of some heterocyclic chalcone analogues alone and in combination with antibiotics

A series of simple heterocyclic chalcone analogues have been synthesized by Claisen Schmidt condensation reactions between substituted benzaldehydes and heteroaryl methyl ketones and evaluated for their antibacterial activity. The structures of the synthesized chalcones were established by IR and ¹H-NMR analysis. The biological data shows that compounds p₅, f₆ and t₅ had strong activities against both susceptible and resistant Staphylococcus aureus strains, but not activity against a vancomycin and methicillin resistant Staphylococcus aureus isolated from a human sample. The structure and activity relationships confirmed that compounds f₅, f₆ and t₅ are potential candidates for future drug discovery and development.

No relationship exists between PBP 2a amounts expressed in different MRSA strains obtained clinically and their beta-lactam MIC values

After establishing a linear relationship between the amount of penicillin-binding protein (PBP) 2a and membrane proteins of methicillin-resistant Staphylococcus aureus (MRSA) COL by dot-blot analysis using an antibody against PBP 2a, we determined the PBP 2a quantities in membrane fractions prepared from 14 different MRSA cells. Methicillin-sensitive S. aureus ATCC 6538P was used as a quality control strain. The amounts of PBP 2a diverged among the strains, and no relationship to beta-lactam MIC values were observed in the corresponding strains.

Different antibacterial actions of isoflavones isolated from Erythrina poeppigiana against methicillin-resistant Staphylococcus aureus

AIMS

To screen six isoflavones isolated from Erythrina poeppigiana (Leguminosae) for their antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA).

METHODS AND RESULTS

Stem bark of E. poeppigiana was macerated with acetone and the methylene chloride-soluble fraction of the residue was applied to repeated silica gel column chromatography and eluted. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined by a broth dilution method. Inactive compounds that failed inhibiting bacterial growth at 25 microg ml(-1) were further investigated for their combination effects with methicillin and oxacillin. Of the isolated isoflavones, 5,7,4'-trihydroxy-8,3'-di(gamma,gamma-dimethylallyl)isoflavone (isolupalbigenin) exhibited the highest anti-MRSA activity (MICs: 1.56-3.13 microg ml(-1); MBCs: 6.25-12.5 microg ml(-1)), followed by 5,7,4'-trihydroxy-6-gamma,gamma-dimethylallylisoflavone (erythrinin B). Inactive compounds were combined with methicillin or oxacillin, 5,4'-dihydroxy-(3'',4''-dihydro-3''-hydroxy)-2'',2''-dimethylpyrano[5'',6'':6,7]isoflavone (M-Wi-2) intensifying the susceptibility of MRSA strains to these antibiotics. In all but one strain, the MIC values of methicillin were reduced from > or =100 to 6.25-12.5 microg ml(-1) in the presence of M-Wi-2 (25 microg ml(-1)).

CONCLUSIONS

Isoflavones from E. poeppigiana showed two different antibacterial activities against MRSA: direct growth inhibition and intensification of methicillin sensitivity.

SIGNIFICANCE AND IMPACT OF THE STUDY

Isolupalbigenin and M-Wi-2 could lead to the development of compounds for new approaches against MRSA infection.

Variation in synergistic activity by flavone and its related compounds on the increased susceptibility of various strains of methicillin-resistant Staphylococcus aureus to beta-lactam antibiotics

We found that some flavonoids had a weak antibacterial effect on methicillin-resistant Staphylococcus aureus (MRSA), but that at sub-MIC concentrations they greatly increased the susceptibility of these strains to beta-lactam antibiotics. Flavone showed diverse synergistic effects on the susceptibility of MRSA to beta-lactam antibiotics. The variation of the synergistic effects of the flavones to increase the susceptibility of strains of MRSA to beta-lactam antibiotics coincided with their varying effects on growth-inhibition of these strains. Based on these findings, we have proposed a model for the mechanisms of high resistance of MRSA to beta-lactams and the massive reduction in the beta-lactams MIC caused by flavones.

Alkyl gallates, intensifiers of beta-lactam susceptibility in methicillin-resistant Staphylococcus aureus

We found that ethyl gallate purified from a dried pod of tara (Caesalpinia spinosa) intensified beta-lactam susceptibility in methicillin-resistant and methicillin-sensitive strains of Staphylococcus aureus (MRSA and MSSA strains, respectively). This compound and several known alkyl gallates were tested with MRSA and MSSA strains to gain new insights into their structural functions in relation to antimicrobial and beta-lactam susceptibility-intensifying activities. The maximum activity of alkyl gallates against MRSA and MSSA strains occurred at 1-nonyl and 1-decyl gallate, with an MIC at which 90% of the isolates tested were inhibited of 15.6 microg/ml. At concentrations lower than the MIC, alkyl gallates synergistically elevated the susceptibility of MRSA and MSSA strains to beta-lactam antibiotics. Such a synergistic activity of the alkyl gallates appears to be specific for beta-lactam antibiotics, because no significant changes were observed in the MICs of other classes of antibiotics examined in this study. The length of the alkyl chain was also associated with the modifying activity of the alkyl gallates, and the optimum length was C5 to C6. The present work clearly demonstrates that the length of the alkyl chain has a key role in the elevation of susceptibility to beta-lactam antibiotics.