Antibacterial single-bead screening

Design, synthesis and evaluation of carbazole derivatives as potential antimicrobial agents

Five series of novel carbazole derivatives containing an aminoguanidine, dihydrotriazine, thiosemicarbazide, semicarbazide or isonicotinic moiety were designed, synthesised and evaluated for their antimicrobial activities. Most of the compounds exhibited potent inhibitory activities towards different bacterial strains (including one multidrug-resistant clinical isolate) and one fungal strain with minimum inhibitory concentrations (MICs) between 0.5 and 16 µg/ml. Compounds 8f and 9d showed the most potent inhibitory activities (MICs of 0.5–2 µg/ml). Furthermore, compounds 8b, 8d, 8f, 8k, 9b and 9e with antimicrobial activities were not cytotoxic to human gastric cancer cell lines (SGC-7901 and AGS) or a normal human liver cell line (L-02). Structure–activity relationship analyses and docking studies implicated the dihydrotriazine group in increasing the antimicrobial potency and reducing the toxicity of the carbazole compounds. In vitro enzyme activity assays suggested that compound 8f binding to dihydrofolate reductase might account for the antimicrobial effect.

Synthesis, characterization and evaluation of 1,3,5-triazine aminobenzoic acid derivatives for their antimicrobial activity

Background

Replacement of chloride ions in cyanuric chloride give several variants of 1,3,5-triazine derivatives which were investigated as biologically active small molecules. These compounds exhibit antimalarial, antimicrobial, anti-cancer and anti-viral activities, among other beneficial properties. On the other hand, treatment of bacterial infections remains a challenging therapeutic problem because of the emerging infectious diseases and the increasing number of multidrug-resistant microbial pathogens. As multidrug-resistant bacterial strains proliferate, the necessity for effective therapy has stimulated research into the design and synthesis of novel antimicrobial molecules.

Results

1,3,5-Triazine 4-aminobenzoic acid derivatives were prepared by conventional method or by using microwave irradiation. Using microwave irradiation gave the desired products in less time, good yield and higher purity. Esterification of the 4-aminobenzoic acid moiety afforded methyl ester analogues. The s-triazine derivatives and their methyl ester analogues were fully characterized by FT-IR, NMR (¹H-NMR and ¹³C-NMR), mass spectra and elemental analysis. All the synthesized compounds were evaluated for their antimicrobial activity. Some tested compounds showed promising activity against Staphylococcus aureus and Escherichia coli.

Conclusions

Three series of mono-, di- and trisubstituted s-triazine derivatives and their methyl ester analogues were synthesized and fully characterized. All the synthesized compounds were evaluated for their antimicrobial activity. Compounds (10), (16), (25) and (30) have antimicrobial activity against S. aureus comparable to that of ampicillin, while the activity of compound (13) is about 50% of that of ampicillin. Compounds (13) and (14) have antimicrobial activity against E. coli comparable to that of ampicillin, while the activity of compounds (9–12) and (15) is about 50% of that of ampicillin. Furthermore, minimum inhibitory concentrations values for clinical isolates of compounds (10), (13), (14), (16), (25) and (30) were measured. Compounds (10) and (13) were more active against MRSA and E. coli than ampicillin. Invitro cytotoxicity results revealed that compounds (10) and (13) were nontoxic up to 250 µg/mL (with SI = 10) and 125 µg/mL (with SI = 5), respectively.Graphical abstract

Design, discovery, modelling, synthesis, and biological evaluation of novel and small, low toxicity s-triazine derivatives as HIV-1 non-nucleoside reverse transcriptase inhibitors

A set of top-ranked compounds from a multi-objective in silico screen was experimentally tested for toxicity and the ability to inhibit the activity of HIV-1 reverse transcriptase (RT) in cell-free assay and in cell-based assay using HIV-1 based virus-like particles. Detailed analysis of a commercial sample that indicated specific inhibition of HIV-1 reverse transcription revealed that a minor component that was structurally similar to that of the main compound was responsible for the strongest inhibition. As a result, novel s-triazine derivatives were proposed, modelled, discovered, and synthesised, and their antiviral activity and cellular toxicity were tested. Compounds 18a and 18b were found to be efficient HIV-1 RT inhibitors, with an IC50 of 5.6±1.1μM and 0.16±0.05μM in a cell-based assay using infectious HIV-1, respectively. Compound 18b also had no detectable toxicity for different human cell lines. Their binding mode and interactions with the RT suggest that there was strong and adaptable binding in a tight (NNRTI) hydrophobic pocket. In summary, this iterative study produced structural clues and led to a group of non-toxic, novel compounds to inhibit HIV-RT with up to nanomolar potency.

Synthesis of Novel Derivatives of Imidazo[2,1-c][1,2,4]Triazine from Biologically Active 4-Arylidene-2-Hydrazino-1-Phenyl-1H-Imidazol-5(4H)-Ones and Evaluation of their Antimicrobial Activity

4-Arylidene-2-hydrazino-1-phenyl-1H-imidazolin-5(4H)-ones were synthesised and used as key intermediates for the synthesis of novel imidazo[2,1-c][1,2,4]triazine derivatives. The new imidazo[2,1-c][1,2,4]triazine derivatives were obtained via the reaction of the hydrazino derivatives with pyruvic acid, chloroacetyl chloride and phenacyl bromide derivatives respectively. Structures of the newly synthesised compounds were confirmed using spectral data as well as elemental analysis. Seven compounds were evaluated for their antimicrobial activity with minimum inhibitory concentration (MIC) values against several reference strains of bacteria and fungi, with ampicillin, gentamicin and amphotericin B used as comparison drugs. It was observed that most of the evaluated compounds showed high antibacterial as well as antifungal activities. 6-(4-Chlorobenzylidene)-4-(4-methylphenyl)-8-phenyl-6,8-dihydroimidazo-[2,1-c][1,2,4] triazin-7(2H)-one was the most potent compound with high inhibition zones and low MIC values.

Synthesis and Preliminary Biological Evaluation of 1,3,5-Triazine Amino Acid Derivatives to Study Their MAO Inhibitors

Three series of 4,6-dimethoxy-, 4,6-dipiperidino- and 4,6-dimorpholino-1,3,5-triazin-2-yl) amino acid derivatives were synthesized and characterized. A preliminary study for their monoamine oxidase inhibitory activity showed that compounds 7, 18, and 25 had MAO-A inhibition activity comparable to that of the standard clorgyline, with apparently more selective inhibitory activity toward MAO-A than MAO-B and no significant acute toxicity.

The ESI CAD fragmentations of protonated 2,4,6-tris(benzylamino)- and tris(benzyloxy)-1,3,5-triazines involve benzyl-benzyl interactions: a DFT study

The electrospray ionization collisionally activated dissociation (CAD) mass spectra of protonated 2,4,6-tris(benzylamino)-1,3,5-triazine (1) and 2,4,6-tris(benzyloxy)-1,3,5-triazine (6) show abundant product ion of m/z 181 (C(14) H(13)(+)). The likely structure for C(14) H(13)(+) is α-[2-methylphenyl]benzyl cation, indicating that one of the benzyl groups must migrate to another prior to dissociation of the protonated molecule. The collision energy is high for the 'N' analog (1) but low for the 'O' analog (6) indicating that the fragmentation processes of 1 requires high energy. The other major fragmentations are [M + H-toluene](+) and [M + H-benzene](+) for compounds 1 and 6, respectively. The protonated 2,4,6-tris(4-methylbenzylamino)-1,3,5-triazine (4) exhibits competitive eliminations of p-xylene and 3,6-dimethylenecyclohexa-1,4-diene. Moreover, protonated 2,4,6-tris(1-phenylethylamino)-1,3,5-triazine (5) dissociates via three successive losses of styrene. Density functional theory (DFT) calculations indicate that an ion/neutral complex (INC) between benzyl cation and the rest of the molecule is unstable, but the protonated molecules of 1 and 6 rearrange to an intermediate by the migration of a benzyl group to the ring 'N'. Subsequent shift of a second benzyl group generates an INC for the protonated molecule of 1 and its product ions can be explained from this intermediate. The shift of a second benzyl group to the ring carbon of the first benzyl group followed by an H-shift from ring carbon to 'O' generates the key intermediate for the formation of the ion of m/z 181 from the protonated molecule of 6. The proposed mechanisms are supported by high resolution mass spectrometry data, deuterium-labeling and CAD experiments combined with DFT calculations.

Hydrogel of ketoconazole and PAMAM dendrimers: formulation and antifungal activity

Ketoconazole (KET), an imidazole derivative with well-known antifungal properties, is lipophilic and practically insoluble in water, therefore its clinical use has some practical disadvantages. The aim of the present study was to investigate the influence of PAMAM-NH₂ and PAMAM-OH dendrimers generation 2 and generation 3 on the solubility and antifungal activity of KET and to design and evaluate KET hydrogel with PAMAM dendrimers. It was shown that the surface charge of PAMAM dendrimers strongly affects their influence on the improvement of solubility and antifungal activity of KET. The MIC and MFC values obtained by broth dilution method indicate that PAMAM-NH₂ dendrimers significantly (up to 16-fold) increased the antifungal activity of KET against Candida strains (e.g., in culture Candida albicans 1103059/11 MIC value was 0.008 μg/mL and 0.064 μg/mL, and MFC was 2 μg/mL and 32 μg/mL for KET in 10 mg/mL solution of PAMAM-NH₂ G2 and pure KET, respectively). Antifungal activity of designed KET hydrogel with PAMAM-NH₂ dendrimers measured by the plate diffusion method was definitely higher than pure KET hydrogel and than commercial available product. It was shown that the improvement of solubility and in the consequence the higher KET release from hydrogels seems to be a very significant factor affecting antifungal activity of KET in hydrogels containing PAMAM dendrimers.

Injectable PAMAM dendrimer-PEG hydrogels for the treatment of genital infections: formulation and in vitro and in vivo evaluation

Local intravaginal drug therapy is preferred for treatment of ascending genital infections during pregnancy. In the present study, an in situ forming biodegradable hydrogel for sustained release of amoxicillin in the cervicovaginal region is described. A generation 4 poly(amidoamine) [G4-(NH(2))(64)] dendrimer with peripheral thiopyridyl terminations is cross-linked with 8-arm polyethylene glycol (PEG) bearing thiol terminations. The hydrogels were formulated and tested in vivo in a pregnant guinea pig model for volume, retention times, biodegradation, tolerability and transport across fetal membrane. The physicochemical characterization of the hydrogels was carried out using differential calorimetry, SEM, and confocal imaging. The hydrogels offer antibacterial activity arising from sustained release of amoxicillin from gels. The in vivo studies in guinea pig showed that 100-200 μL of gel sufficiently covered the cervicovaginal region with a residence time of at least 72 h and gel was primarily retained in the maternal tissues without crossing the fetal membranes into the fetus. The dendrimer gels were stable up to 72 h, and the in vivo biodegradation of gel occurred after 72 h; this correlated well with the in vitro degradation pattern. The pH of the vagina was not altered upon application of the gel, and none of the animals aborted up to 72 h after application of gel. The histological evaluation of the cervical tissues showed absence of edema in the epithelial cell layer, no sloughing of the epithelial or superficial mucous layer, and absence of necrosis and infiltration of inflammatory cells in the submucosal layers, confirming that tissues were tolerant to the gel. The immunohistofluorescence images showed the localization of the gel components on the superficial mucified epithelial layer. The cross-linking density and swelling of hydrogels was impacted by the polymer content, and the 10% hydrogels exhibited the highest cross-link density. The in vitro drug release studies carried out using Franz diffusion cells showed that amoxicillin release from 6 and 10% gels was sustained for 240 h as compared to 3% gels. As the polymer concentration increased to 10%, the release pattern from gels approached diffusion controlled mechanism with diffusional exponent n = 0.49. In conclusion, the biodegradable in situ forming hydrogels of the present study offer a therapeutic option to provide sustained localized delivery of amoxicillin intracervically to the pregnant woman for the treatment of ascending genital infections.

Synthesis of novel tripodal-benzimidazole from 2,4,6-tris(p-formylphenoxy)-1,3,5-triazine: structural, electrochemical and antimicrobial studies

Four new tripodal-benzimidazole derivatives were synthesized by Schiff base reaction between 2,4,6-tris(p-formylphenoxy)-1,3,5-triazine (TRIPOD) and different diamine derivatives. The structures of the obtained compounds were identified by FT-IR, (1)H NMR, (13)C NMR and UV-vis spectral data, thermal analysis and elemental analysis. Electrochemical behaviors of the compounds were studied by cyclic voltammetry in DMF including 0.1 M [NBu(4)] [PF(6)]. The voltammograms showed peaks having similar characteristics except tripodal-benzimidazole including -NO(2) derivative. In addition, their antimicrobial activities were evaluated by using the standard disk diffusion method in dimethylformamide media. The activities were determined against 4 bacteria cultures by comparing to those of gentamycin.

Inhibition of bacterial growth and intramniotic infection in a guinea pig model of chorioamnionitis using PAMAM dendrimers

Dendrimers have emerged as topical microbicides to treat vaginal infections. This study explores the in vitro, in vivo antimicrobial activity of PAMAM dendrimers, and the associated mechanism. Interestingly, topical cervical application of 500 microg of generation-4 neutral dendrimer (G(4)-PAMAM-OH) showed potential to treat the Escherichia coli induced ascending uterine infection in guinea pig model of chorioamnionitis. Amniotic fluid collected from different gestational sacs of infected guinea pigs posttreatment showed absence of E. coli growth in the cultures plated with it. The cytokine level [tumor necrosis factor (TNFalpha) and interleukin (IL-6 and IL-1beta)] in placenta of the G(4)-PAMAM-OH treated animals were comparable to those in healthy animals while these were notably high in infected animals. Since, antibacterial activity of amine-terminated PAMAM dendrimers is known, the activity of hydroxyl and carboxylic acid terminated PAMAM dendrimers was compared with it. Though the G(4)-PAMAM-NH(2) shows superior antibacterial activity, it was found to be cytotoxic to human cervical epithelial cell line above 10 microg/mL, while the G(4)-PAMAM-OH was non-cytotoxic up to 1mg/mL concentration. Cell integrity, outer (OM) and inner (IM) membrane permeabilization assays showed that G(4)-PAMAM-OH dendrimer efficiently changed the OM permeability, while G(4)-PAMAM-NH(2) and G(3.5)-PAMAM-COOH damaged both OM and IM causing the bacterial lysis. The possible antibacterial mechanism are G(4)-PAMAM-NH(2) acts as polycation binding to the polyanionic lipopolysaccharide in E. coli, the G(4)-PAMAM-OH forms hydrogen bonds with the hydrophilic O-antigens in E. coli membrane and the G(3.5)-PAMAM-COOH acts as a polyanion, chelating the divalent ions in outer cell membrane of E. coli. This is the first study which shows that G(4)-PAMAM-OH dendrimer acts as an antibacterial agent.

Transport and biodistribution of dendrimers across human fetal membranes: implications for intravaginal administration of dendrimer-drug conjugates

Dendrimers are emerging as promising topical antimicrobial agents, and as targeted nanoscale drug delivery vehicles. Topical intravaginal antimicrobial agents are prescribed to treat the ascending genital infections in pregnant women. The fetal membranes separate the extra-amniotic space and fetus. The purpose of the study is to determine if the dendrimers can be selectively used for local intravaginal application to pregnant women without crossing the membranes into the fetus. In the present study, the transport and permeability of PAMAM (poly (amidoamine)) dendrimers, across human fetal membrane (using a side by side diffusion chamber), and its biodistribution (using immunofluorescence) are evaluated ex-vivo. Transport across human fetal membranes (from the maternal side) was evaluated using Fluorescein (FITC), an established transplacental marker (positive control, size approximately 400 Da) and fluorophore-tagged G(4)-PAMAM dendrimers (approximately 16 kDa). The fluorophore-tagged G(4)-PAMAM dendrimers were synthesized and characterized using (1)H NMR, MALDI TOF MS and HPLC analysis. Transfer was measured across the intact fetal membrane (chorioamnion), and the separated chorion and amnion layers. Over a 5 h period, the dendrimer transport across all the three membranes was less than <3%, whereas the transport of FITC was relatively fast with as much as 49% transport across the amnion. The permeability of FITC (7.9 x 10(-7) cm(2)/s) through the chorioamnion was 7-fold higher than that of the dendrimer (5.8 x 10(-8) cm(2)/s). The biodistribution showed that the dendrimers were largely present in interstitial spaces in the decidual stromal cells and the chorionic trophoblast cells (in 2.5-4 h) and surprisingly, to a smaller extent internalized in nuclei of trophoblast cells and nuclei and cytoplasm of stromal cells. Passive diffusion and paracellular transport appear to be the major route for dendrimer transport. The overall findings further suggest that entry of drugs conjugated to dendrimers would be restricted across the human fetal membranes when administered topically by intravaginal route, suggesting new ways of selectively delivering therapeutics to the mother without affecting the fetus.

Synthesis and antibacterial activity of various substituted s-triazines

Series of substituted-s-triazines (1-22) were synthesized and evaluated for their in vitro antibacterial activity against six representative Gram-positive and Gram-negative bacterial strains. Many compounds have displayed comparable antibacterial activity against Bacillus sphaericus and significantly active against other tested organisms with reference to streptomycin.

Dendrimers Based on [1,3,5]-Triazines

A comprehensive and chronological account of dendrimers based on [1,3,5]-triazines is provided. Synthetic strategies to install the triazine through cycloaddition, cyclotrimerization, and nucleophilic aromatic substitution of cyanuric chloride are discussed. Motivations and applications of these architectures are surveyed, including the preparation of supra-molecular assemblies in the solution and solid states and their use in medicines, advanced materials, and separations when anchored to solid supports.

Synthesis and antibacterial activity of 2,4,6-tri substituted s-triazines

Various 2,4,6-tri substituted s-triazines were synthesized and screened for antibacterial activity against Gram-positive and Gram-negative organisms. These s-triazine derivatives displayed high in vitro antibacterial activities comparable to penicillin and streptomycin against tested microorganisms.