Synthesis, characterization and in vitro antimicrobial evaluation of new compounds incorporating oxindole nucleus

New compounds incorporating with the oxindole nucleus were synthesized via the reaction of substituted isatins [5-methyl-, 5-chloro- and 1-hydroxymethyl isatins] with different nucleophiles. The structures of the newly compounds were elucidated on the basis of FTIR, (1)H NMR, (13)CMR spectral data, GC/MS and chemical analysis. Investigation of antimicrobial activity of the new compounds was evaluated using broth dilution technique in terms of minimal inhibitory concentration (MIC) count against four pathogenic bacteria and two pathogenic fungi. Most of the new compounds are significantly active against bacteria and fungi. MIC showed that compound (4a) possesses higher effect on Gram-positive bacteria Bacillus cereus than the selected antibacterial agent sulphamethoxazole, whereas compound (11c) possesses more activity against Gram-negative bacteria Shigella dysenterie.     

Alkaloids from Ruta montana

Two known and four new quinoline and 4-quinolone type alkaloids were isolated from Ruta montana collected from Rommani (Morocco). The known compounds were 1-methyl-4-methoxy-2-quinolone and evolitrine. The structures of the new compounds were established from 1D and 2D NMR experiments including HMQC, HMBC and MS spectral methods as 2-(nonan-8-one)-(1H)-4-quinolone, 2-(nonan-8-one)-4-methoxy-quinoline, 2-(nonan-8-one)-N-methyl-4-quinolone and 2-(decan-9-one)-N-methyl-4-quinolone.     

A combination effect of epigallocatechin gallate, a major compound of green tea catechins, with antibiotics on Helicobacter pylori growth in vitro

Since green tea catechins are known to have antimicrobial activity against a variety of microorganisms, their possible effects on Helicobacter pylori in combination with antibiotics were examined. Fifty-six clinical isolates of H. pylori, including 19 isolates highly resistant to metronidazole (MTZ) and/or clarithromycin (CLR), were used to determine in vitro sensitivity to tea catechins. The MIC90 of both epigallocatechin gallate (EGCg) and epicatechin gallate (ECg) was 100 microg/ml. However, other tea catechins tested did not show any anti-H. pylori activity. Highly antibiotic-resistant clinical isolates showed a similar sensitivity to both EGCg and ECg. The kinetic study of antibacterial activity in liquid cultures revealed a relatively slow but strong activity on the growth of H. pylori. In combination with sub-MIC of amoxicillin (AMX), the antibacterial activity of AMX was significantly enhanced by the presence of EGCg. To estimate the general combination effect between EGCg and other antibiotics, such as MTZ and CLR, on the antibacterial activity against clinical isolates, the fraction inhibitory concentration (FIC) was determined by checkerboard study. The FIC indexes showed additive effects between EGCg and antibiotics tested. These results indicatethat EGCg may be a valuable therapeutic agent against H. pylori infection.     

Synthesis and in vitro selective anti-Helicobacter pylori activity of pyrazoline derivatives

In order to develop new anti-Helicobacter pylori agents, a series of N1-substituted 3,5-diphenyl pyrazolines P1-P13 was prepared and evaluated for their antibacterial activity. All synthesized compounds showed little or no activity against different species of Gram-positive and Gram-negative bacteria of clinical relevance and against various strains of pathogenic fungi. The same derivatives exhibited a significant degree of activity against a range of H. pylori strains, including those resistant to the reference compound metronidazole. Among the prepared compounds those with an N1-acetyl group and a 4-methoxy substituent in the 5-phenyl ring showed the best activity against H. pylori metronidazole resistant strains in the 1-4 microg/mL MIC range.     

Antimicrobial activity of hydrophobic xanthones from Cudrania cochinchinensis against Bacillus subtilis and methicillin-resistant Staphylococcus aureus

Ten xanthones with one or two isoprenoid groups and a prenylated benzophenone isolated from roots of Cudrania cochinchinensis (Moraceae) were tested for their antimicrobial activities against Bacillus subtilis and methicillin-resistant Staphylococcus aureus (MRSA). Among these compounds, gerontoxanthone H exhibited considerable antibacterial activity against B. subtilis (MIC = 1.56 microg/ml). Four xanthones, gerontoxanthone I, toxyloxanthone C, cudraxanthone S, and 1,3,7-trihydroxy-2-prenylxanthone, showed weak antibacterial activity against the bacterium (MICs = 3.13-6.25 microg/ml). These compounds also exhibited similar MIC values against methicillin-sensitive S. aureus, MRSAs, and Micrococcus luteus.     

Synthesis and anti-Helicobacter pylori activity of 5-(nitroaryl)-1,3,4-thiadiazoles with certain sulfur containing alkyl side chain

A series of 5-(nitroaryl)-1,3,4-thiadiazoles bearing certain sulfur containing alkyl side chain similar to pendent residue in tinidazole molecule were synthesized and evaluated against Helicobacter pylori using disk diffusion method. The synthesized compounds were also evaluated for their antibacterial, antifungal and cytotoxic effects. Study of the structure-activity relationships of this series of compounds indicated that both the structure of the nitroaryl unit and the pendent group on 2-position of 1,3,4-thiadiazole ring dramatically impact the anti-H. pylori activity. While compound 7a containing 2-[2-(ethylsulfonyl)ethylthio]-side chain from nitrothiophene series was the most potent compound tested against clinical isolates of H. pylori, however, nitroimidazoles 6c and 7c were found to be more promising compounds because of their respectable anti-H. pylori activity besides less cytotoxic effects.     

Quinoline alkaloids and cytotoxic lignans from Haplophyllum tuberculatum

Three quinoline alkaloids and two lignan lactones were isolated from Haplophyllum tuberculatum. Physicochemical and spectral evidence established the structures of two of the alkaloids as a new quinoldione, 3-(1′,1′-dimethylallyl)-3-(3″,3″-dimethylallyl)-1,2,3,4-tetrahydro-2,4-quinoldione and the known 4-(3′,3′-dimethylallyloxy)-3-(3″,3″-dimethylallyl)-2(1H)-quinolone. The former was shown to undergo facile [3,3]-sigmatotropic transformation into the latter. The remaining compounds were identified as the known Polygamain, kusunokinin and 1-methyl-2-n-nonyl-4(1H)-quinolone.     

Anti-Helicobacter pylori activity of the methanolic extract of Geum iranicum and its main compounds

Geum iranicum Khatamsaz, belonging to the Rosaceae family, is an endemic plant of Iran. The methanol extract of the roots of this plant showed significant activity against one of the clinical isolates of Helicobacter pylori which was resistant to metronidazole. The aim of this study was the isolation and evaluation of the major compounds of G. iranicum effective against H. pylori. The compounds were isolated using various chromatographic methods and identified by spectroscopic data (1H and 13C NMR, HMQC, HMBC, EI-MS). An antimicrobial susceptibility test was performed employing the disk diffusion method against clinical isolates of H. pylori and a micro dilution method against several Gram-positive and Gram-negative bacteria; additionally the inhibition zone diameters (IZD) and minimum inhibitory concentrations (MIC) values were recorded. Nine compounds were isolated: two triterpenoids, uvaol and niga-ichigoside F1, three sterols, beta-sitosterol, beta-sitosteryl acetate, and beta-sitosteryl linoleate, one phenyl propanoid, eugenol, one phenolic glycoside, gein, one flavanol, (+)-catechin, and sucrose. The aqueous fraction, obtained by partitioning the MeOH extract with water and chloroform, was the most effective fraction of the extract against all clinical isolates of H. pylori. Further investigation of the isolated compounds showed that eugenol was effective against H. pylori but gein, diglycosidic eugenol, did not exhibit any activity against H. pylori. The subfraction D4 was the effective fraction which contained tannins. It appeared that tannins were probably the active compounds responsible for the anti-H. pylori activity of G. iranicum. The aqueous fraction showed a moderate inhibitory activity against both Gram-positive and Gram-negative bacteria. The MIC values indicated that Gram-positive bacteria including Staphylococcus aureus, Staphylococcus epidermidis, and Bacillus subtilis are more susceptible than Gram-neagative bacteria including Escherichia coli and Pseudomonas aeruginosa.     

Susceptibility in vitro of Helicobacter pylori to cetylpyridinium chloride

The antimicrobial agent cetylpyridinium chloride (CPC) which is used in therapy of oro-pharyngeal infections and for antiseptic treatment of the oral cavity is active against different bacterial species. Determination of the minimal inhibitory concentration (MIC) using the agar dilution technique revealed that the gastric pathogen Helicobacter pylori in vitro is highly susceptible to CPC as indicated by an MIC of 10 microM (3.4 microg ml(-1)) which was significantly lower than the MIC of CPC against other bacterial species, which were analyzed in comparison to H. pylori. Bacteria of the genus Campylobacter, various Streptococcus spp., Staphylococcus aureus and Escherichia coli showed higher MICs ranging from 100 microM to 2 mM. In summary, this finding renders CPC-containing drugs candidates possibly useful for eradication or for the prevention of transmission of the gastric pathogen.     

Synthesis,characterization and in vitro antimicrobial evaluation of new compounds incorporating oxindole nucleus

New compounds incorporating with the oxindole nucleus were synthesized via the reaction of substituted isatins [5-methyl-, 5-chloro- and 1-hydroxymethyl isatins] with different nucleophiles. The structures of the newly compounds were elucidated on the basis of FTIR, ¹H NMR, ¹³CMR spectral data, GC/MS and chemical analysis. Investigation of antimicrobial activity of the new compounds was evaluated using broth dilution technique in terms of minimal inhibitory concentration (MIC) count against four pathogenic bacteria and two pathogenic fungi. Most of the new compounds are significantly active against bacteria and fungi. MIC showed that compound (4a) possesses higher effect on Gram-positive bacteria Bacillus cereus than the selected antibacterial agent sulphamethoxazole, whereas compound (11c) possesses more activity against Gram-negative bacteria Shigella dysenterie.     

Synthesis and antimicrobial properties of imidazolium and pyrrolidinonium salts

For the purpose of developing new disinfectants and antiseptics, we searched for compounds having high bactericidal activity against gram-positive bacteria, gram-negative bacteria, and fungi. Three different series of quaternary imidazolium and pyrrolidinonium salts were synthesized: series A (1-alkyl-3-methylimidazolium chlorides and bromides); series B (1-alkyl-2-methyl-3-hydroxyethylimidazolium chlorides); and series C (N-alkyl-N-hydroxyethylpyrrolidinonium). Series B and C were newly designed. These three series were tested to evaluate their antibacterial and antifungal properties for the first time. Seven microbial strains were used in the study: Escherichia coli KCTC1924, Salmonella typhimurium KCTC1926, Staphylococcus aureus 209 KCTC1916, Staphylococcus aureus R209 KCTC1928, Bacillus subtilis KCTC1914, Candida albicans KCTC1940, and Chlorella regularis. The antimicrobial efficiency was measured by bacterial and fungal growth inhibition expressed as minimal inhibitory concentration (MIC) values. Series A and B imidazolium salts had very good antimicrobial activity against the examined Gram-negative bacteria, Gram-positive bacteria, and fungi. Also the pyrrolidinonium salt was found to have low MIC for some of tested microorganisms. The antibacterial and antifungal active properties of the salts depend upon the structure of functional groups and the alkyl chain length in the imidazolium and pyrrolidinonium ring. Among the synthesized quaternary imidazolium and pyrrolidinonium salts, the imidazolium salts containing a long alkyl chain and the introduction of a hydroxyethyl chain and methyl group into the imidazolium ring structure leads to broad spectrum active antimicrobial agents which not only have bacteriostatic properties but could be powerful bactericides.     

Antibacterial activity of hydrolyzable tannins derived from medicinal plants against Helicobacter pylori

Helicobacter pylori is a major etiological agent in gastroduodenal disorders. In this study, we isolated 36 polyphenols and 4 terpenoids from medicinal plants, and investigated their antibacterial activity against H. pylori in vitro. All hydrolyzable tannins tested demonstrated promising antibacterial activity against H. pylori. Monomeric hydrolyzable tannins revealed especially strong activity. Other compounds demonstrated minimal antibacterial activity with a few exceptions. A monomeric hydrolyzable tannin, Tellimagrandin I demonstrated time- and dose-dependent bactericidal activity against H. pylori in vitro. On the other hand, hydrolyzable tannins did not affect the viability of MKN-28 cells derived from human gastric epithelium. Hydrolyzable tannins, therefore, have potential as new and safe therapeutic regimens against H. pylori infection. Furthermore, we investigated effects of hydrolyzable tannins on lipid bilayer membranes. All the hydrolyzable tannins tested demonstrated dose-dependent membrane-damaging activity. However, it remains to be elucidated whether their membrane-damaging activity directly contributes to their antibacterial action.     

Enhanced clearing of Helicobacter pylori after omeprazole plus roxithromycin treatment

The in vitro antibacterial activity of omeprazole against eight strains of Helicobacter pylori was evaluated. Minimum inhibitory concentration (MIC) values were 32 micrograms/ml and 64 micrograms/ml (MIC50 and MIC90 respectively). We performed a randomized single blind study comparing the efficacy of omeprazole alone (for 4 weeks) or combined with roxithromycin (for 2 weeks) in the treatment of duodenal ulcer and chronic active gastritis associated with H. pylori infection, H. pylori was eradicated in 75% of patients treated with omeprazole alone whereas the patients treated with the combination of these drugs were completely free from H. pylori at the end of the therapy.     

Formation of edulinine and furoquinoline alkaloids from quinoline derivatives by cell suspension cultures of Ruta graveolens

The formation of furoquinoline alkaloids and of edulinine, elaborated by cell suspension cultures of Ruta graveolens, was found to occur by way of 4-hydroxy-2-quinolone. Other substrates transformed to furoquinolines included 4-hydroxy- and 4-methoxy-3-(3-methyl-2-butenyl)-2-quinolone, known earlier as natural precursors in studies with whole plants. Involvement of dictamnine as a natural precursor of 8-methoxydictamnine (γ-fagarine) and skimmianine was proved using ¹⁴C-labelled compounds. Edulinine in the cell suspensions was formed from such substrates as 4-hydroxy-N-methyl-2-quinolone, 4-hydroxy-3-(3-methyl-2-butenyl)-N-methyl-2-quinolone and its 4- methyl ether; this is probably the natural biosynthetic sequence. Changes in alkaloid yields were noted upon prolonged subculturing.     

Selective and effective bactericidal activity of the cobalt (II) cation against Helicobacter pylori

BACKGROUND: Although the anti-Helicobacter pylori activity of bismuth is well established, the therapeutic potential of other metal ions against the organism is not known. MATERIALS AND METHODS: We measured the minimum inhibitory concentrations of a series of metal ions, including several cobalt (II) compounds against four type strains and seven clinical isolates of H. pylori using three standard broth culture media and a defined medium. Other intestinal bacteria were also investigated for specificity of action. RESULTS: Cobalt chloride had marked activity against H. pylori (minimum inhibitory concentration range was 0.03-1.0 mg/l). The effect was specific because other transition metals had no effect and other intestinal bacteria were not affected by cobalt chloride. Activity was attributable to free cobalt ions as ligands inhibited activity in proportion to their affinity for the ions. Inhibition of cobalt activity was also observed in the presence of nickel, in a dose dependent fashion. However, cobalt activity was not directed towards the nickel-dependent urease enzyme because its effect was similar in wild-type and urease negative mutant strains of H. pylori. Finally, the viability of H. pylori was reduced at the same rate with 2 mg/l cobalt as with 1 mg/l amoxicillin. CONCLUSIONS: Cobalt competes for nickel in its acquisition by H. pylori, but mediates toxicity in a nonurease dependent fashion. As cobalt MIC is similar to some antibiotics and 10 to a hundred times lower than for bismuth, cobalt may represent an effective form of therapy for H. pylori infection.     

Effect of hydrogen peroxide on antibacterial activities of Canadian honeys

Honey is recognized as an efficacious topical antimicrobial agent in the treatment of burns and wounds. The antimicrobial activity in some honeys depends on the endogenous hydrogen peroxide content. This study was aimed to determine whether honey's hydrogen peroxide level could serve as a honey-specific, activity-associated biomarker that would allow predicting and assessing the therapeutic effects of honey. Using a broth microdilution assay, I analyzed antibacterial activities of 42 Canadian honeys against two bacterial strains: Escherichia coli (ATCC 14948) and Bacillus subtilis (ATCC 6633). The MIC90 and MIC50 were established from the dose-response relationship between antibacterial activities and honey concentrations. The impact of H2O2 on antibacterial activity was determined (i) by measuring the levels of H2O2 before and after its removal by catalase and (ii) by correlating the results with levels of antibacterial activities. Canadian honeys demonstrated moderate to high antibacterial activity against both bacterial species. Both MIC90 and MIC50 revealed that the honeys exhibited a selective growth inhibitory activity against E. coli, and this activity was strongly influenced by endogenous H2O2 concentrations. Bacillus subtilis activity was marginally significantly correlated with H2O2 content. The removal of H2O2 by catalase reduced the honeys' antibacterial activity, but the enzyme was unable to completely decompose endogenous H2O2. The 25%-30% H2O2 "leftover" was significantly correlated with the honeys' residual antibacterial activity against E. coli. These data indicate that all Canadian honeys exhibited antibacterial activity, with higher selectivity against E. coli than B. subtilis, and that these antibacterial activities were correlated with hydrogen peroxide production in honeys. Hydrogen peroxide levels in honey, therefore, is a strong predictor of the honey's antibacterial activity.     

Design,synthesis and molecular modeling studies on novel moxifloxacin derivatives as potential antibacterial and antituberculosis agents

Twenty-one novel alkyl/acyl/sulfonyl substituted fluoroquinolone derivatives were designed, synthesized and evaluated for their anti-tuberculosis and antibacterial activity. The targeted compounds were synthesized by the introduction of alkyl, acyl or sulfonyl moieties to the basic secondary amine moiety of moxifloxacin. Structures of the compounds were enlightened by FT-IR, ¹H NMR, ¹³C NMR and HRMS data besides elemental analysis. Compounds were initially tested in vitro for their anti-mycobacterial activity against Mycobacterium tuberculosis H37Rv using microplate alamar blue assay. Minimal inhibitory concentration (MIC) values of all compounds were found between > 25.00–0.39 µg/mL while compounds 1, 2 and 13 revealed an outstanding activity against M. tuberculosis H37Rv with MIC values of 0.39 µg/mL. Activities of compounds 1–21 against to a number of Gram-positive and Gram-negative bacteria and fast growing mycobacterium strain were also investigated by agar well diffusion and microdilution methods. According to antimicrobial activity results, compound 13 was found the most potent derivative with a IC₅₀ value of <1.23 μg/mL against Staphylococcus aureus and clinical strain of methicillin-resistant clinical strain of S. aureus.     

Antimicrobial compounds from Eremophila serrulata

We report a search for antimicrobial compounds in the Australian plant Eremophila serrulata. Bioassay directed fractionation of a diethyl ether extract prepared from the leaves of E. serrulata led to the isolation of two compounds, an omicron-naphthoquinone, 9-methyl-3-(4-methyl-3-pentenyl)-2,3-dihydronaphtho[1,8-bc]pyran-7,8-dione (2), and a serrulatane diterpenoid, 20-acetoxy-8-hydroxyserrulat-14-en-19-oic acid (3). Two other known serrulatane-type diterpenoids, 8,20-dihydroxyserrulat-14-en-19-oic acid (4) and 8,20-diacetoxyserrulat-14-en-19-oic acid (5) were also isolated. None of these compounds had previously been tested for antimicrobial activity. Compounds 2-5 showed antimicrobial activity against Staphylococcus aureus (ATCC 29213) with minimum inhibitory concentrations (MICs) ranging from 15.6 to 250mug/mL. Compound 2 was the most active with an MIC of 15.6mug/mL and a minimum bactericidal concentration (MBC) of 125mug/mL. This compound also showed antimicrobial activity against other Gram-positive bacteria including Streptococcus pyogenes, and Streptococcus pneumoniae. No activity was observed for this compound against all Gram-negative bacteria tested.     

Synthesis and preliminary evaluation of some pyrazine containing thiazolines and thiazolidinones as antimicrobial agents

A series of N'-[3,4-disubstituted-1,3-thiazol-2(3H)-ylidene]-2-(pyrazin-2-yloxy)acetohydrazide 11-66 and N'-[(2Z)-3-(4-bromophenyl)-4-oxo-1,3-thiazolidin-2-ylidene]-2-(pyrazin-2-yloxy)acetohydrazide 68-74 were synthesized using appropriate synthetic route. The entire test compounds 11-66 and 68-74 were assayed in vitro for antibacterial activity against two different strains of Gram-negative (E. coli and S. typhi), Gram-positive (S. aureus and B. subtilis) bacteria and the antimycobacterial activity was evaluated against H(37)Rv strain of Mycobacterium tuberculosis. The minimum inhibitory concentration (MIC) was determined for test compounds and for reference standards. The test compounds showed significant antibacterial and antimycobacterial activity against the microbial strains used, when tested in vitro. In general, pyrazine ring and substituted thiazoline ring are essential for antimicrobial activity. Among the compounds tested, compounds 11, 12 and 40 were found to be most potent. The toxicity of most potent compounds 11, 12 and 40 were determined using hemolytic assay and minimal hemolytic concentration (MHCs) were determined. The test compounds were found to be nontoxic up to a dose level of 250 microg/mL.     

Design, synthesis and antimicrobial activities of nitroimidazole derivatives containing 1,3,4-oxadiazole scaffold as FabH inhibitors

Nitroimidazoles and their derivatives have drawn continuing interest over the years because of their varied biological activities, recently found application in drug development for antimicrobial chemotherapeutics and antiangiogenic hypoxic cell radiosensitizers. In order to search for novel antibacterial agents, we designed and synthesized a series of secnidazole analogs based on oxadiazole scaffold (4-21). Among these compounds, 4 and 7-21 were reported for the first time. These compounds were tested for antibacterial activities against Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis and Staphylococcus aureus. This new nitroimidazole derivatives class demonstrated strong antibacterial activities. Escherichia coli β-ketoacyl-acyl carrier protein synthase III (FabH) inhibitory assay and docking simulation indicated that the compounds 2-(2-methoxyphenyl)-5-((2-methyl-5-nitro-1H-imidazol-1-yl)methyl)-1,3,4-oxadiazole (11) with MIC of 1.56-3.13 μg/mL against the tested bacterial strains and 2-((2-methyl-5-nitro-1H-imidazol-1-yl)methyl)-5-(2-methylbenzyl)-1,3,4-oxadiazole (12) with MIC of 1.56-6.25 μg/mL were most potent inhibitors of Escherichia coli FabH.