In vitro activity of salicylamide derivatives against vancomycin-resistant enterococci

A series of 13 salicylamide derivatives was assessed for antibacterial activity against three isolates of vancomycin-resistant Enterococcus faecalis (VRE) and Enterococcus faecalis ATCC 29212 as a quality standard. The minimum inhibitory concentration was determined by the broth microdilution method with subsequent subcultivation of aliquots to assess minimum bactericidal concentration. The growth kinetics was established by the time-kill assay. Ampicillin, ciprofloxacin, tetracycline and vancomycin were used as the reference antibacterial drugs. Three of the investigated compounds showed strong bacteriostatic activity against VRE (0.199–25?µM) comparable to or more potent than ampicillin and ciprofloxacin. In addition, these compounds were tested for synergistic effect with vancomycin, ciprofloxacin and tetracycline, while 5-chloro-2-hydroxy-N-[4-(trifluoromethyl)phenyl]benzamide showed the highest potency as well as synergistic activity with vancomycin against VRE 368. Screening of the cytotoxicity of the most effective compounds was performed using human monocytic leukemia THP-1 cells, and based on LD₅₀ values, it can be stated that the compounds have insignificant toxicity against human cells.     

Exploring N-Acylhydrazone Derivatives Against Clinical Resistant Bacterial Strains

Bacterial multiresistance is a health problem worldwide that demands new antimicrobials for treating bacterial-related infections. In this study, we evaluated the antimicrobial activity and the theoretical toxicology profile of N-substituted-phenylamino-5-methyl-1H-1,2,3-triazole-4-carbohydrazide derivatives against gram-positive and gram-negative bacteria clinical strains. On that purpose we determined the minimum inhibitory (MIC) and bactericidal (MBC) concentrations, the in vitro cytotoxicity, and in silico risk profiles, also comparing with antimicrobial agents of clinical use. Among the 16 derivatives analyzed, four nitrofurans (N–H–FUR–NO₂, N–Br–FUR–NO₂, N–F–FUR–NO₂, N–Cl–FUR–NO₂) showed promising MIC and MBC values (MIC = MBC = 1–16 μg/mL). The experimental data revealed the potential of these derivatives, which were comparable to the current antimicrobials with similar bactericidal and bacteriostatic profiles. Therefore, these molecules may be feasible options to be explored for treating infections caused by multiresistant strains. Our in vitro and in silico toxicity reinforced these results as these derivatives presented low cytotoxicity against human macrophages and low theoretical risk profile for irritant and reproductive effects compared to the current antimicrobials (e.g., vancomycin and ciprofloxacin). The molecular modeling analysis also revealed positive values for their theoretical druglikeness and drugscore. The presence of a 5-nitro-2-furfur-2-yl group seems to be essential for the antimicrobial activity, which pointed these acylhydrazone derivatives as promising for designing more potent and safer compounds.     

Tandem action of glycosyltransferases in the maturation of vancomycin and teicoplanin aglycones: novel glycopeptides

The glycopeptides vancomycin and teicoplanin are clinically important antibiotics. The carbohydrate portions of these molecules affect biological activity, and there is great interest in developing efficient strategies to make carbohydrate derivatives. To this end, genes encoding four glycosyltransferases, GtfB, C, D, E, were subcloned from Amycolatopsis orientalis strains that produce chloroeremomycin (GtfB, C) or vancomycin (GtfD, E) into Escherichia coli. After expression and purification, each glycosyltransferase (Gtf) was characterized for activity either with the aglycones (GtfB, E) or the glucosylated derivatives (GtfC, D) of vancomycin and teicoplanin. GtfB efficiently glucosylates vancomycin aglycone using UDP-glucose as the glycosyl donor to form desvancosaminyl-vancomycin (vancomycin pseudoaglycone), with k(cat) of 17 min(-1), but has very low glucosylation activity, < or = 0.3 min(-1), for an alternate substrate, teicoplanin aglycone. In contrast, GtfE is much more efficient at glucosylating both its natural substrate, vancomycin aglycone (k(cat) = 60 min(-1)), and an unnatural substrate, teicoplanin aglycone (k(cat) = 20 min(-1)). To test the addition of the 4-epi-vancosamine moiety by GtfC and GtfD, synthesis of UDP-beta-L-4-epi-vancosamine was undertaken. This NDP-sugar served as a substrate for both GtfC and GtfD in the presence of vancomycin pseudoaglycone (GtfC and GtfD) or the glucosylated teicoplanin scaffold, 7 (GtfD). The GtfC product was the 4-epi-vancosaminyl form of vancomycin. Remarkably, GtfD was able to utilize both an unnatural acceptor, 7, and an unnatural nucleotide sugar donor, UDP-4-epi-vancosamine, to synthesize a novel hybrid teicoplanin/vancomycin glycopeptide. These results establish the enzymatic activity of these four Gtfs, begin to probe substrate specificity, and illustrate how they can be utilized to make variant sugar forms of both the vancomycin and the teicoplanin class of glycopeptide antibiotics.     

Synthesis and evaluation of methyl ether derivatives of the vancomycin, teicoplanin, and ristocetin aglycon methyl esters

A series of methyl ether derivatives of the vancomycin, teicoplanin, and ristocetin aglycon methyl esters was synthesized and their antimicrobial activity was established. These derivatives exhibit increased activity against VanB resistant strains of bacteria equipotent with that observed with sensitive bacteria.     

Design,synthesis, and antibacterial activity of 2,5-dihydropyrrole formyl hydroxyamino derivatives as novel peptide deformylase inhibitors

The synthesis and antibacterial activity of 2,5-dihydropyrrole formyl hydroxyamino derivatives are reported. The antibacterial activities of these derivatives were evaluated, and some of these derivatives showed better in vitro antibacterial activity than existing drugs, including penicillin, ciprofloxacin, vancomycin, and linezolid.     

The dimerization of semisynthetic eremomycin derivatives studied by the electrospray ionization mass spectrometry and its effect on their antibacterial activity

The dimerization constants for glycopeptide antibiotics vancomycin, ristocetin, and eremomycin and nine semisynthetic eremomycin derivatives were determined by the electrospray ionization mass spectrometry; the constants for natural antibiotics turned out to be close to those previously determined by NMR. No correlation between these dimerization constants and antibacterial activities of all the compounds toward the clinical strains of Gram-positive bacteria was found.     

Antibacterial activity of 3-methylbenzo[d]thiazol-methylquinolinium derivatives and study of their action mechanism

The increasing incidence of multidrug resistant bacterial infection renders an urgent need for the development of new antibiotics. To develop small molecules disturbing FtsZ activity has been recognized as promising approach to search for antibacterial of high potency systematically. Herein, a series of novel quinolinium derivatives were synthesized and their antibacterial activities were investigated. The compounds show strong antibacterial activities against different bacteria strains including MRSA, VRE and NDM-1 Escherichia coli. Among these derivatives, a compound bearing a 4-fluorophenyl group (A2) exhibited a superior antibacterial activity and its MICs to the drug-resistant strains are found lower than those of methicillin and vancomycin. The biological results suggest that these quinolinium derivatives can disrupt the GTPase activity and dynamic assembly of FtsZ, and thus inhibit bacterial cell division and then cause bacterial cell death. These compounds deserve further evaluation for the development of new antibacterial agents targeting FtsZ.     

Study of dimerization of polysynthetic derivatives of the antibiotic eremomycin by ESI MS and its role in elucidating antibacterial activity

The dimerization constants for glycopeptide antibiotics vancomycin, ristocetin, and eremomycin and nine semisynthetic eremomycin derivatives were determined by the electrospray ionization mass spectrometry; the constants for natural antibiotics turned out to be close to those previously determined by NMR. No correlation between these dimerization constants and antibacterial activities of all the compounds toward the clinical strains of Gram-positive bacteria was found.     

The functional vanGCd cluster of Clostridium difficile does not confer vancomycin resistance

vanG_Cd, a cryptic gene cluster highly homologous to the vanG gene cluster of Enterococcus faecalis is largely spread in Clostridium difficile. Since emergence of vancomycin resistance would have dramatic clinical consequences, we have evaluated the capacity of the vanG_Cd cluster to confer resistance. We showed that expression of vanG_Cd is inducible by vancomycin and that VanG_Cd, VanXY_Cd and VanT_Cd are functional, exhibiting D‐Ala : D‐Ser ligase, D,D‐dipeptidase and D‐Ser racemase activities respectively. In other bacteria, these enzymes are sufficient to promote vancomycin resistance. Trans‐complementation of C. difficile with the vanC resistance operon of Enterococcus gallinarum faintly impacted the MIC of vancomycin, but did not promote vancomycin resistance in C. difficile. Sublethal concentration of vancomycin led to production of UDP‐MurNAc‐pentapeptide[D‐Ser], suggesting that the vanG_Cd gene cluster is able to modify the peptidoglycan precursors. Our results indicated amidation of UDP‐MurNAc‐tetrapeptide, UDP‐MurNAc‐pentapeptide[D‐Ala] and UDP‐MurNAc‐pentapeptide[D‐Ser]. This modification is passed on the mature peptidoglycan where a muropeptide Tetra‐Tetra is amidated on the meso‐diaminopimelic acid. Taken together, our results suggest that the vanG_Cd gene cluster is functional and is prevented from promoting vancomycin resistance in C. difficile.     

Characterisation of the selective binding of antibiotics vancomycin and teicoplanin by the VanS receptor regulating type A vancomycin resistance in the enterococci

A-type resistance towards “last-line” glycopeptide antibiotic vancomycin in the leading hospital acquired infectious agent, the enterococci, is the most common in the UK. Resistance is regulated by the VanR_AS_A two-component system, comprising the histidine sensor kinase VanS_A and the partner response regulator VanR_A. The nature of the activating ligand for VanS_A has not been identified, therefore this work sought to identify and characterise ligand(s) for VanS_A. In vitro approaches were used to screen the structural and activity effects of a range of potential ligands with purified VanS_A protein. Of the screened ligands (glycopeptide antibiotics vancomycin and teicoplanin, and peptidoglycan components N-acetylmuramic acid, D-Ala-D-Ala and Ala-D-y-Glu-Lys-D-Ala-D-Ala) only glycopeptide antibiotics vancomycin and teicoplanin were found to bind VanS_A with different affinities (vancomycin 70 μM; teicoplanin 30 and 170 μM), and were proposed to bind via exposed aromatic residues tryptophan and tyrosine. Furthermore, binding of the antibiotics induced quicker, longer-lived phosphorylation states for VanS_A, proposing them as activators of type A vancomycin resistance in the enterococci.     

Characteristics of the MRSA clone with reduced susceptibility to vancomycin

The MIC of vancomycin was determined for all S. aureus strains isolated during 1997 in one hospital. MIC values for most isolates were in the range of 0.5-2 mg/l. In 18 strains, MIC was = 6 mg/L. All these strains were MRSA. Recently described VISA strains possessed MIC values for vancomycin equal or higher than 8 mg/l and such strains were not detected in the investigated group. Although strains with MIC = 6 mg/l are not VISA, but they are candidate for reduced vancomycin susceptibility, e.g. during therapy in compromised patients. Analysis of DNA of these strains by pulsed-field gel electrophoresis (PFGE) revealed that 15 of them shared a significant similarity, allowing to place them in the same group. The comparison data of phage patterns as well as antibiotic resistance patterns strongly suggest that all these strains were derivatives of a single clone.     

Novel ether derivatives of mannopeptimycin glycopeptide antibiotic

Novel ether derivatives of mannopeptimycin glycopeptide were synthesized to probe their SAR. Many of these derivatives exhibited potent antibacterial activity against methicillin resistant and vancomycin resistant strains. These ether derivatives were prepared via reductive ring cleavage of acetals to give a mixture of 6-O, 4-O, 3-O, and 2-O-ether isomers. Both 6-O-ether and 4-O-ether showed significantly enhanced antibacterial activity over the parent and the isovalerate esters.     

Identifying the Interaction of Vancomycin With Novel pH-Responsive Lipids as Antibacterial Biomaterials Via Accelerated Molecular Dynamics and Binding Free Energy Calculations

Nano-drug delivery systems have proven to be an efficient formulation tool to overcome the challenges with current antibiotics therapy and resistance. A series of pH-responsive lipid molecules were designed and synthesized for future liposomal formulation as a nano-drug delivery system for vancomycin at the infection site. The structures of these lipids differ from each other in respect of hydrocarbon tails: Lipid1, 2, 3 and 4 have stearic, oleic, linoleic, and linolenic acid hydrocarbon chains, respectively. The impact of variation in the hydrocarbon chain in the lipid structure on drug encapsulation and release profile, as well as mode of drug interaction, was investigated using molecular modeling analyses. A wide range of computational tools, including accelerated molecular dynamics, normal molecular dynamics, binding free energy calculations and principle component analysis, were applied to provide comprehensive insight into the interaction landscape between vancomycin and the designed lipid molecules. Interestingly, both MM-GBSA and MM-PBSA binding affinity calculations using normal molecular dynamics and accelerated molecular dynamics trajectories showed a very consistent trend, where the order of binding affinity towards vancomycin was lipid4?>?lipid1?>?lipid2?>?lipid3. From both normal molecular dynamics and accelerated molecular dynamics, the interaction of lipid3 with vancomycin is demonstrated to be the weakest (?G_binding?=??2.17 and ?11.57, for normal molecular dynamics and accelerated molecular dynamics, respectively) when compared to other complexes. We believe that the degree of unsaturation of the hydrocarbon chain in the lipid molecules may impact on the overall conformational behavior, interaction mode and encapsulation (wrapping) of the lipid molecules around the vancomycin molecule. This thorough computational analysis prior to the experimental investigation is a valuable approach to guide for predicting the encapsulation ability, drug release and further development of novel liposome-based pH-responsive nano-drug delivery system with refined structural and chemical features of potential lipid molecule for formulation development.     

Biotransformation of withaferin-a by a culture ofArthrobacter simplex

Arthrobacter simplex biotransformed withaferin-A under submerged conditions to 7 new derivatives while 4,27-di-O-acetylwithaferin-A was transformed to another 9 derivatives. The melting point of all these substances was determined, along with R_F values and colour reactions with 4-anisaldehyde reagent. Derivatives also differed in their biological effects on P388 cells. A marked inhibitory effect on the synthesis of nucleic acids and proteins in the leukemia cells P388 was found in 12 out of 16 new derivatives.     

Synthesis and biological evaluation of pyrazole linked benzothiazole-β-naphthol derivatives as topoisomerase I inhibitors with DNA binding ability

A series of new pyrazole linked benzothiazole-β-naphthol derivatives were designed and synthesized using a simple, efficient and ecofriendly route under catalyst-free conditions in good to excellent yields. These derivatives were evaluated for their cytotoxicity on selected human cancer cell lines. Among those, the derivatives 4j, 4k and 4l exhibited considerable cytotoxicity with IC₅₀ values ranging between 4.63 and 5.54?µM against human cervical cancer cells (HeLa). Structure activity relationship was elucidated by varying different substituents on benzothiazoles and pyrazoles. Further, flow cytometric analysis revealed that these derivatives induced cell cycle arrest in G2/M phase and spectroscopic studies such as UV–visible, fluorescence and circular dichroism studies showed that these derivatives exhibited good DNA binding affinity. Additionally, these derivatives can effectively inhibit the topoisomerase I activity. Viscosity studies and molecular docking studies demonstrated that the derivatives bind with the minor groove of the DNA.     

Understanding and manipulating glycopeptide pathways: the example of the dalbavancin precursor A40926

Glycopeptide antibiotics represent an important class of microbial compounds produced by several genera of actinomycetes. The emergence of resistance to glycopeptides among enterococci and staphylococci has prompted the search for second-generation drugs of this class and semi-synthetic derivatives are currently under clinical trials. Dalbavancin is obtained by chemical modification of the natural glycopeptide A40926, produced by a Nonomuraea sp. Recently, there has been considerable progress in the elucidation of biosynthesis of glycopeptide antibiotics; several gene clusters have been characterized, thus providing an understanding of the biosynthesis of these chemically complex molecules. Furthermore, such investigations have yielded the first glycopeptide derivatives produced by genetic or enzymatic intervention. We have isolated and characterized the dbv clusters, involved in the formation of the glycopeptides A40926. The development of a gene-transfer system for Nonomuraea sp. has allowed the manipulation of the A40926 pathway. New derivatives were obtained by inactivating selected dbv genes. In addition, our data suggest differences in the biosynthetic routes for heptapeptide formation between the vancomycin and the teicoplanin families of glycopeptides.     

Vancomycin as chiral selector for enantioselective separation of selected profen nonsteroidal anti-inflammatory drugs in capillary liquid chromatography

The chiral selector vancomycin was used either as mobile phase additive or bound as a chiral stationary phase (CSP) for the stereoselective separation of seven racemic nonsteroidal anti-inflammatory drugs (NSAIDs), fenoprofen, carprofen, flurbiprofen, indoprofen, flobufen, ketoprofen, and suprofen, by capillary liquid chromatography. The effect of the type of stationary phase, the chiral column Chirobiotic V or the achiral stationary phases Nucleosil 100 C8 HD and Nucleosil 100 C18 HD, and the concentration of vancomycin in the mobile phase on separation of the drug enantiomers were evaluated. All the drugs, except flobufen, were successfully enantioseparated on Nucleosil 100 C8 HD with 4 mM vancomycin present in the mobile phase (composed of methanol and buffer) in the reversed phase mode. On the vancomycin-bonded chiral stationary phase, it was difficult to get enantioseparations of the profen NSAIDs. However, flobufen gave better enantioseparation on the vancomycin CSP. The better enantioresolution of the majority of profen derivatives on the achiral columns with vancomycin added to the mobile phase can be attributed in particular to the higher separation efficiency of this capillary chromatographic system. In addition, vancomycin dimers, formed in the mobile phase, seem to offer a better steric arrangement for stereoselective interaction to these analytes than the vancomycin bonded on the CSP. These substantial differences in the CS structure significantly influence the chiral discrimination mechanism.     

Antibacterial activity of G6-quaternary ammonium derivatives of a lipophilic vancomycin analogue

A series of G6-amino derivatives of a lipophilic vancomycin analogue was prepared. Antibacterial activity of the analogues was inversely proportional to the degree of substitution of the G6-nitrogen. The fully substituted (quaternary) analogues were essentially inactive against vanA phenotype VREF strains but retained substantial activity against other bacteria, a profile reminiscent of teicoplanin.     

Biological evaluation and molecular modelling study of thiosemicarbazide derivatives as bacterial type IIA topoisomerases inhibitors

In the present article, we describe the inhibitory potency of nine thiosemicarbazide derivatives against bacterial type IIA topoisomerases, their antibacterial profile and molecular modelling evaluation. We found that one of the tested compounds, compound 7, significantly inhibits activity of Staphylococcus aureus DNA gyrase with an IC₅₀ below 15?μM. Besides, this compound displays antibacterial activity on reference Staphylococuss spp. and Enterococcus faecalis strains as well as clinical S. aureus isolates at non-cytotoxic concentrations in mammalian cells with MIC values ranging from 16 to 32?μg/mL thereby indicating, in some cases, equipotent or even more effective action than standard drugs such as vancomycin, ampicillin and nitrofurantoin. The computational studies showed that both molecular geometry and the electron density distribution have a great impact on antibacterial activity of thiosemicarbazide derivatives.     

Design,synthesis and anti-Alzheimer's disease activity study of xanthone derivatives based on multi-target strategy

A series of xanthone derivatives were designed, synthesized and evaluated as multifunctional ligands against Alzheimer’s disease (AD). In vitro studies showed all xanthone derivatives had good metal chelating property and exhibited selective inhibitory activity against Acetylcholinesterase (AChE). In particular, compound 2a showed the highest inhibitory activity against AChE, and the IC₅₀ value was (0.328 ± 0.001) μM, which was comparable to tacrine. Kinetic analysis and molecular docking studies indicated that these derivatives targeted both the catalytically active site (CAS) and the peripheral anion site (PAS) of AChE. Moreover, all derivatives showed higher anti-oxidative activity than vitamin C. Furthermore, copper complex had higher anti-AChE activity and antioxidant activity. Thus, these xanthone derivatives are potential multi-targeted-directed ligands for further development for the treatment of AD.