Biology-oriented drug synthesis and evaluation of secnidazole esters as novel enzyme inhibitors.

The identification of novel compounds that can inhibit physiologically and metabolically important drug targets or enzymes has prime importance in medicinal chemistry. With this aim, a range of secnidazole esters 1-30 were synthesized under the heading of biology-oriented drug synthesis by the 1,1'-carbonyldiimidazole-mediated coupling reaction between secnidazole and varyingly benzoic acid derivatives. All compounds were screened for inhibitory activity against human carbonic anhydrase (hCA) I and II, acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and α-glucosidase. The results indicate that all the synthesized compounds showed potent inhibitory activities against all targets, as compared to the standard inhibitors, revealed by IC50 values. Ki values of the secnidazole derivatives 1-30 for hCA I, hCA II, AChE, BChE, and α-glucosidase enzymes were obtained in the ranges of 47.37-190.74, 44.38-198.21, 12.14-68.37, 8.04-61.53, and 7.78-45.91 nM, respectively. To assess the enzyme-ligand interactions, the optimized most active compounds 2, 3, 8, 9, 14, 17, and 23 were subjected to molecular docking studies with modeled AChE, BChE, hCA I, hCA II, and α-glucosidase enzymes, where several important and key interactions were monitored with amino acid residues of each target enzyme.

Synthesis of New Hybrid Derivatives from Metronidazole and Eugenol Analogues as Trypanocidal Agents.

BACKGROUND: The search for new drug compounds is always challenging and there are several different strategies that involve the most varied and creative approaches in medicinal chemistry. One of them is the technique of molecular hybridisation: forming a hybrid compound from two or more pharmacophoric subunits. These hybrids may maintain the characteristics of the original compound and preferably show improvements to its pharmacological action, with reduced side effects and lower toxicity when compared to the original components. This study specifically focuses on synthesising hybrid molecules which demonstrate trypanocidal activity against the epimastigote and trypomastigote forms of Trypanosoma cruzi. METHODS: In this context, this study centres on the synthesis of a novel structural scaffold via molecular hybridisation; by using a triazole species to link a metronidazole unit to a eugenol analogue unit, the objective being to combine their therapeutic properties into a new molecular structure. The resulting hybrid molecules were evaluated against T. cruzi which is responsible for high incidences of trypanosomiasis in tropical countries such as Brazil. RESULTS: The results of this study showed an improvement in the anti-parasitic activity of the hybrid compounds with the best result coming from hybrid compounds [8] and [9], which present an activity similar to the control drug benznidazole. The new compounds, utilising a triazole species as a coupling connector, demonstrated promising results and has highlighted the path for planning similar structural patterns to investigate new compounds. CONCLUSIONS: In summary, we can conclude that the synthesised hybrid compounds demonstrate that using a triazole to link metronidazole with natural phenols, produces hybrid molecules that are promising as a new class of compounds of therapeutic interest for further investigation.

A Quality by Design Approach of Metronidazole Bigel and Assessment of Antimicrobial Study Utilizing Box-behnken Design.

OBJECTIVE: The present investigation aimed to prepare metronidazole (MTZ) topical bigel for the effective delivery of MTZ and to study the effect of applied variables as per statistical design. The study also signifies the implementation of the statistical method using the Quality by Design technique for MTZ bigel. METHODS: The MTZ bigels were prepared as per the runs suggested by Box Behnken design (BBD) using statistical software. A total of 28 runs were suggested by the BBD, considering sodium carboxymethylcellulose (Na CMC), guar gum, hydrogel and RPM as independent variables. The prepared bigels were evaluated for organoleptic properties, percentage drug content, spreadability, viscosity, percentage in-vitro drug release, and antimicrobial efficacy. Model selectivity was ascertained by p-value considering responses along with predicted R2 and adjusted R2 values.The fitting of model was ascertained by F-value as well as "lack of fit" was carried out to find out the suitability of the experimental design. Furthermore, the characteristic distribution of data was ascertained by the "normal plot of residual" method. The compatibility of MTZ and excipients in bigels was confirmed by FTIR and the crystalline nature of MTZ in formulations was studied by DSC and XRD studies. Furthermore, the dispersion of bigel was assessed by the SEM study. RESULTS: The effect of independent variables on spreadability (mm), viscosity (cp), pH, drug release in 6 hours (%)and drug content (%) was evaluated. The optimized formulation was selected and evaluated by a polynomial equation while considering the p-value. These variables showed a significant effect on responses. A less significant difference was observed (6.37, 14463, 6.97, 86.29, and 67.47, respectively, for spreadability, viscosity, pH, and percentage drug release and % drug content) between the observed and predicted values indicating the model's suitability. The prepared bigels were found to be compatible and globules uniformly dispersed throughout the bigel. CONCLUSION: The 3D response surface design ascertained the optimal MTZ bigel at 1.25g of NaCMC, 0.5g of guargum, 37.5g hydrogel, and 1000 RPM. The selected bigel showed good antimicrobial efficacy against S. Aureus and may be considered an effective delivery vehicle for MTZ.

Metronidazole-conjugates: A comprehensive review of recent developments towards synthesis and medicinal perspective.

Nitroimidazoles based compounds remain a hot topic of research in medicinal chemistry due to their numerous biological activities. Moreover, many clinical candidates based on this chemical core have been reported to be valuable in the treatment of human diseases. Metronidazole (MTZ) derived conjugates demonstrated a potential application in medicinal chemistry research over the last decade. In this review, we summarize the synthesis, key structure-activity-relationship (SAR) and associated biological activities such as antimicrobial, anticancer, antidiabetic, anti-inflammatory, anti-HIV and anti-parasitic (Anti-trichomonas, antileishmanial, antiamoebic and anti-giardial) of explored MTZ-conjugates. The molecular docking analysis is also presented simultaneously, which will assist in developing an understanding towards designing of new MTZ-conjugates for target-based drug discovery against multiple disease areas.

Synthesis of metronidazole based thiazolidinone analogs as promising antiamoebic agents.

Metronidazole and its derivatives are widely used for the treatment of amoebiasis. However, metronidazole is considered as the standard drug but it has many side effects. The present study describes the synthesis of a series of metronidazole based thiazolidinone analogs via Knoevenagel condensation of 4-[2-(2-methyl-5-nitro-1H-imidazole-1-yl)ethoxy]benzaldehyde 1 with various thiazolidinone derivatives 2-14 to get the new scaffold (15-27) having better activity and lesser toxicity. Six compounds have shown better efficacy and lesser cytotoxicity than the standard drug metronidazole towards HM1: IMSS strain of Entamoeba histolytica. These compounds may combat the problem of drug resistance and might be effective in identifying potential alternatives for future drug discovery against EhOASS.

Metronidazole and Secnidazole Carbamates: Synthesis, Antiprotozoal Activity, and Molecular Dynamics Studies.

We prepared a series of 10 carbamates derivatives based on two common antiprotozoal drugs: metronidazole (1-5) and secnidazole (6-10). The compounds were tested in vitro against a set of two amitochondriate protozoa: Giardia duodenalis and Trichomonas vaginalis. Compounds 1-10 showed strong antiprotozoal activities, with potency values in the low micromolar-to-nanomolar range, being more active than their parent drugs. Metronidazole carbamate (1) was the most active of the series, with nanomolar activities against G. duodenalis (IC50 = 460 nM) and T. vaginalis (IC50 = 60 nM). The potency of compound 1 was 10 times greater than that of metronidazole against both parasites. None of compounds showed in vitro cytotoxicity against VERO cells tested at 100 µM. Molecular dynamics of compounds 1-10, secnidazole, and metronidazole onto the ligand binding site of pyruvate-ferredoxin oxidoreductase of T. vaginalis and the modeled -tubulin of G. duodenalis revealed putative molecular interactions with key residues in the binding site of both proteins implicated in the mode of action of the parent drugs.

Synthesis, Biological Evaluation, Structure-Activity Relationship, and Mechanism of Action Studies of Quinoline-Metronidazole Derivatives Against Experimental Visceral Leishmaniasis.

In our efforts to identify novel chemical scaffolds for the development of antileishmanial agents, a series of quinoline-metronidazole hybrid compounds was synthesized and tested against the murine model of visceral leishmaniasis. Among all synthesized derivatives, 15b and 15i showed significant antileishmanial efficacy against both extracellular promastigote (IC50 9.54 and 5.42 µM, respectively) and intracellular amastigote (IC50 9.81 and 3.75 µM, respectively) forms of Leishmania donovani with negligible cytotoxicity toward the host (J774 macrophages, Vero cells). However, compound 15i effectively inhibited the parasite burden in the liver and spleen (>80%) of infected BALB/c mice. Mechanistic studies revealed that 15i triggers oxidative stress which induces bioenergetic collapse and apoptosis of the parasite by decreasing ATP production and mitochondrial membrane potential. Structure-activity analyses and pharmacokinetic studies suggest 15i as a promising antileishmanial lead and emphasize the importance of quinoline-metronidazole series as a suitable platform for the future development of antileishmanial agents.

Metronidazole aryloxy, carboxy and azole derivatives: Synthesis, anti-tumor activity, QSAR, molecular docking and dynamics studies.

A series of novel metronidazole aryloxy, carboxy and azole derivatives has been synthesized and their cytotoxic activities on three cancer cell lines were evaluated by MTT assay. Compounds 4m, 4l and 4d showed the most potent cytotoxic activity (IC50s less than 100 µg/mL). Apoptosis was also detected for these compounds by flow cytometry. Docking studies were performed in order to propose the probable target protein. In the next step, molecular dynamics simulation was carried out on the proposed target protein, focal adhesion kinase (FAK, PDB code: 2ETM), bound to compound 4m. As, 4m showed a potent cytotoxic activity and an acceptable apoptotic effect, it can be a potential anticancer candidate that may work through inhibition of FAK.

Highly Potent 1H-1,2,3-Triazole-Tethered Isatin-Metronidazole Conjugates Against Anaerobic Foodborne, Waterborne, and Sexually-Transmitted Protozoal Parasites.

Parasitic infections like amebiasis, trichomoniasis, and giardiasis are major health threats in tropical and subtropical regions of the world. Metronidazole (MTZ) is the current drug of choice for amebiasis, giardiasis, and trichomoniasis but it has several adverse effects and potential resistance is a concern. In order to develop alternative antimicrobials, a library of 1H-1,2,3-triazole-tethered metronidazole-isatin conjugates was synthesized using Huisgen's azide-alkyne cycloaddition reaction and evaluated for their amebicidal, anti-trichomonal, and anti-giardial potential. Most of the synthesized conjugates exhibited activities against Trichomonas vaginalis, Tritrichomonas foetus, Entamoeba histolytica, and Giardia lamblia. While activities against T. vaginalis and T. foetus were comparable to that of the standard drug MTZ, better activities were observed against E. histolytica and G. lamblia. Conjugates 9d and 10a were found to be 2-3-folds more potent than MTZ against E. histolytica and 8-16-folds more potent than MTZ against G. lamblia. Further analysis of these compounds on fungi and bacteria did not show inhibitory activity, demonstrating their specific anti-protozoal properties.

99mTc labelled complexes with secnidazole xanthate: Synthesis and evaluation as potential radiotracers to target tumor hypoxia.

In this study, the commercially available secnidazole was successfully converted to secnidazole xanthate (SNXT), in which the xanthate group can act as a bifunctional chelator to coordinate with 99mTc. 99mTc-nitrido complex of SNXT(99mTcN-SNXT) and 99mTc-oxo complex of SNXT(99mTcO-SNXT) were prepared with high radiochemical purity. Both of the complexes were found to be stable in vitro and to exhibit similar hydrophilicity. In addition, comparative in vitro cell uptake studies under anoxic and normoxic conditions demonstrated that both agents were preferentially taken up by hypoxic cells. Biodistribution studies in mice bearing S180 tumor showed 99mTcO-SNXT exhibited a higher tumor uptake and tumor-to-muscle ratio than 99mTcN-SNXT. Furthermore, in SPECT imaging study, 99mTcO-SNXT exhibited a clear accumulation in tumor at 2 h post-injection, suggesting its potential to be a novel hypoxia imaging agent.

Preparation and biological evaluation of metronidazole derivatives with monoterpenes and eugenol.

Two series of metronidazole derivatives (ester derivatives and ether derivatives) were prepared reacting metronidazole and its acetic acid oxidized form with menthol, thymol, carvacrol, and eugenol. Both series of compounds were tested in vitro against two strains of Helicobacter pylori (the ATCC 26695 and P12), and one strain of Clostridium (Clostridium perfringens). Most of the prepared compounds showed biological activity against the targeted bacteria. Compound 11 was highly active against all tested bacterial strains, especially against P12 with IC50 0.0011 µM/ml. Compound 6 was highly active against C. perfringens with MIC 0.0094 nM/ml. Viability test was conducted for compound 11 to test its selectivity for normal human fetal lung fibroblasts (MRC5), and it was found to be non-toxic with IC50 more than 50 µM/ml.

Amino acid conjugated antimicrobial drugs: Synthesis, lipophilicity- activity relationship, antibacterial and urease inhibition activity.

Present work describes the in vitro antibacterial evaluation of some new amino acid conjugated antimicrobial drugs. Structural modification was attempted on the three existing antimicrobial pharmaceuticals namely trimethoprim, metronidazole, isoniazid. Twenty one compounds from seven series of conjugates of these drugs were synthesized by coupling with some selected Boc-protected amino acids. The effect of structural features and lipophilicity on the antibacterial activity was investigated. The synthesized compounds were evaluated against five standard American type culture collection (ATCC) i.e. Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa and Salmonella typhi strains of bacteria. Our results identified a close relationship between the lipophilicity and the activity. Triazine skeleton proved beneficial for the increase in hydrophobicity and potency. Compounds with greater hydrophobicity have shown excellent activities against Gram-negative strains of bacteria than Gram-positive. 4-amino unsubstituted trimethoprim-triazine derivative 7b have shown superior activity with MIC = 3.4 µM (2 µg/mL) for S. aureus and 1.1 µM (0.66 µg/mL) for E. coli. The synthesized compounds were also evaluated for their urease inhibition study. Microbial urease from Bacillus pasteurii was chosen for this study. Triazine derivative 7a showed excellent inhibition with IC50 = 6.23 ±â€¯0.09 µM. Docking studies on the crystal structure of B. pasteurii urease (PDB ID 4UBP) were carried out.

Metronidazole containing pyrazole derivatives potently inhibit tyrosyl-tRNA synthetase: design, synthesis, and biological evaluation.

As an important enzyme in bacterial protein biosynthesis, tyrosyl-tRNA synthetase (TyrRS) has been an absorbing therapeutic target for exploring novel antibacterial agents. A series of metronidazole-based antibacterial agents has been synthesized and identified as TyrRS inhibitors with low cytotoxicity and significant antibacterial activity, especially against Gram-negative organisms. Of the compounds obtained, 4f is the most potent agent which inhibited the growth of Pseudomonas aeruginosa ATCC 13525 (MIC = 0.98 µg/mL) and exhibited TryRS inhibitory activity (IC50  = 0.92 µm). Docking simulation was performed to further understand its potency. Membrane-mediated apoptosis in P. aeruginosa was verified by flow cytometry.

Design, synthesis and evaluation of molecularly targeted hypoxia-activated prodrugs.

Regions of insufficient oxygen supply-hypoxia-occur in diverse contexts across biology in both healthy and diseased organisms. The difference in the chemical environment between a hypoxic biological system and one with normal oxygen levels provides an opportunity for targeting compound delivery to hypoxic regions by using bioreductive prodrugs. Here we detail a protocol for the efficient synthesis of (1-methyl-2-nitro-1H-imidazol-5-yl)methanol, which is a key intermediate that can be converted into a range of 1-methyl-2-nitro-1H-imidazole-based precursors of bioreductive prodrugs. We outline methods for attaching the bioreductive group to a range of functionalities, and we discuss the strategy for positioning of the group on the biologically active parent compound. We have used two parent checkpoint kinase 1 (Chk1) inhibitors to exemplify the protocol. The PROCEDURE also describes a suite of reduction assays, of increasing biological relevance, to validate the bioreductive prodrug. These assays are applied to an exemplar compound, CH-01, which is a bioreductive Chk1 inhibitor. This protocol has broad applications to the development of hypoxia-targeted compounds.

Novel hybrids of metronidazole and quinolones: synthesis, bioactive evaluation, cytotoxicity, preliminary antimicrobial mechanism and effect of metal ions on their transportation by human serum albumin.

A novel series of hybrids of metronidazole and quinolones as antimicrobial agents were designed and synthesized. Most prepared compounds exhibited good or even stronger antimicrobial activities in comparison with reference drugs. Furthermore, these highly active metronidazole-quinolone hybrids showed appropriate ranges of pKa, log P and aqueous solubility to pharmacokinetic behaviors and no obvious toxicity to A549 and human hepatocyte LO2 cells. Their competitive interactions with metal ions to HSA revealed that the participation of Mg(2+) ion in compound 7d-HSA association could result in a concentration increase of free compound 7d. Molecular modeling and experimental investigation of compound 7d with DNA suggested that possible antibacterial mechanism might be in relation with multiple binding sites between bioactive molecules and topo IV-DNA complex.

Synthesis, molecular docking and biological evaluation of metronidazole derivatives containing piperazine skeleton as potential antibacterial agents.

Metronidazole has a broad-spectrum antibacterial activity. Hereby a series of novel metronidazole derivatives were designed and synthesized based on nitroimidazole scaffold in order to find some more potent antibacterial drugs. For these compounds which were reported for the first time, their antibacterial activities against Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis and Staphylococcus aureus were tested. These compounds showed good antibacterial activities against Gram-positive strains. Compound 4m represented the most potent antibacterial activity against S. aureus ATCC 25923 with MIC of 0.003 µg/mL and it showed the most potent activity against S. aureus TyrRS with IC50 of 0.0024 µM. Molecular docking of 4m into S. aureus tyrosyl-tRNA synthetase active site were also performed to determine the probable binding mode.

Synthesis and antibacterial evaluation of amino acid-antibiotic conjugates.

Amino acid conjugates of quinolone, metronidazole and sulfadiazine antibiotics were synthesized in good yields using benzotriazole methodology. All the conjugates were screened for their antibacterial activity using methods adapted from the Clinical and Laboratory Standards Institute. Antibiotic conjugates were tested for activity in four medically relevant organisms; Staphylococcus aureus (RN4220), Escherichia coli (DH5α), Pseudomonas aeruginosa (PAO1), and Bacillus subtilis (168). Several antibiotic conjugates show promising results against several of the strains screened.

Synthesis and bioactive evaluation of novel hybrids of metronidazole and berberine as new type of antimicrobial agents and their transportation behavior by human serum albumin.

A series of novel hybrids of metronidazole and berberine as new type of antimicrobial agents were synthesized and characterized by (1)H NMR, (13)C NMR, IR, MS and HRMS spectra. Bioactive assay manifested that most of the prepared compounds exhibited effective antibacterial and antifungal activities and some showed comparable or superior potency against Methicillin-resistant Staphylococcus aureus to reference drugs Norfloxacin, Chloromycin and Berberine. The transportation behavior of human serum albumin (HSA) to the highly active compound 5g was evaluated and revealed that the association of imidazole derivative 5g with HSA was spontaneous and the electrostatic interactions played important roles in the transportation of HSA to 5g. The calculated parameters indicated that compound 5g could be effectively stored and carried by HSA.

Design, synthesis and antimicrobial activities evaluation of Schiff base derived from secnidazole derivatives as potential FabH inhibitors.

FabH, ß-ketoacyl-acyl carrier protein (ACP) synthase III, is critically important to the initiation of fatty acid biosynthesis and is highly conserved among Gram-positive and Gram-negative bacteria. A series of novel secnidazole derivatives (1-20) were synthesized and fully characterized by spectroscopic methods and elemental analysis. Among these compounds, 6, 8, 11, 13, 14, 16-20 were reported for the first time. These compounds were tested for antibacterial activities against Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis and Staphylococcus aureus. The compounds inhibitory assay and docking simulation indicated that compound 20 (E)-2-(2-methyl-5-nitro-1H-imidazol-1-yl)-N'-(3,4,5-trimethylbenzylidene)acetohydrazide with MIC of 3.13-6.25 µg/mL against the tested bacterial strains was a potent inhibitor of Escherichia coli FabH.

Metronidazole-coumarin conjugates and 3-cyano-7-hydroxy-coumarin act as isoform-selective carbonic anhydrase inhibitors.

Reaction of 6-/7-hydroxycoumarin with metronidazole afforded conjugates which incorporate two interesting chemotypes which may inhibit carbonic anhydrases (CAs, EC 4.2.1.1) due to the presence of the coumarin moiety and possess radiosensitizing effects due to the presence of the nitroazole. Another dual action compound, which may act both as CA inhibitor as well as monocarboxylate transporter inhibitor, is 3-cyano-7-hydroxy-coumarin. These compounds have been investigated as inhibitors of 11 human CA isoforms. Submicromolar inhibition was observed against hCA VA, hCA VB, hCA VI, hCA VII, hCA IX, hCA XII and hCA XIV, whereas isoforms hCA I, II and XIII were not inhibited by these compounds. These coumarins thus act as isoform-selective CA inhibitors with the possibility to target isoforms involved in pathologies such as obesity (CA VA/VB) or cancer (CA IX and XII) without inhibiting the physiologically dominant, highly abundant hCA I and II.