Novel Antitrypanosomal Agents Based on Palladium Nitrofurylthiosemicarbazone Complexes: DNA and Redox Metabolism as Potential Therapeutic Targets

In the search for new therapeutic tools against American Trypanosomiasis palladium complexes with bioactive nitrofuran-containing thiosemicarbazones as ligands were obtained. Sixteen novel palladium (II) complexes with the formulas [PdCl2(HL)] and [Pd(L)2] were synthesized, and the crystal structure of [Pd(5-nitrofuryl-3-acroleine thiosemicarbazone)2] x 3DMSO was solved by X-ray diffraction methods. Most complexes showed higher in vitro growth inhibition activity against Trypanosoma cruzi than the standard drug Nifurtimox. In most cases, the activity of the ligand was maintained or even increased as a result of palladium complexation. In addition, the complexes' mode of antitrypanosomal action was investigated. Although the complexes showed strong DNA binding, all data strongly suggest that the main trypanocidal mechanism of action is the production of oxidative stress as a result of their bioreduction and extensive redox cycling. Moreover, the complexes were found to be irreversible inhibitors of trypanothione reductase.

Trypanosoma cruzi: effect and mode of action of nitroimidazole and nitrofuran derivatives

With the aim of determining the actual target(s) of nitro-group bearing compounds considered as possible leads for the development of drugs against Chagas' disease, we studied in parallel nitrofurans and nitroimidazoles. We investigated nine representative compounds for the following properties: efficacy on different Trypanosoma cruzi strains, redox cyclers, inhibition of respiration, production of corresponding nitroso derivatives and intracellular thiol scavengers. Our results indicate that nifurtimox and related compounds act as redox cyclers, whereas the most active in the series, the 5-nitroimidazole megazol essentially acts as thiol scavenger particularly for trypanothione, the cofactor for trypanothione reductase, an essential enzyme in the detoxification process.

Design and synthesis of a series of melamine-based nitroheterocycles with activity against Trypanosomatid parasites

The parasites that give rise to human African trypanosomiasis (HAT) are auxotrophs for various nutrients from the human host, including purines. They have specialist nucleoside transporters to import these metabolites. In addition to uptake of purine nucleobases and purine nucleosides, one of these transporters, the P2 transporter, can carry melamine derivatives; these derivatives are not substrates for the corresponding mammalian transporters. In this paper, we report the coupling of the melamine moiety to selected nitro heterocycles with the aim of selectively delivering these compounds to the parasites. Some compounds prepared have similar in vitro trypanocidal activities as melarsoprol, the principal drug used against late-stage HAT, with 50% growth inhibitory concentrations in the submicromolar range. Selected compounds were also evaluated in vivo in rodent models infected with Trypanosoma brucei brucei and T. brucei rhodesiense and showed pronounced activity and in two cases were curative without overt signs of toxicity. Compounds were also tested against other trypanosomatid pathogens, Leishmania donovani and Trypanosoma cruzi, and significant activity in vitro was noted for T. cruzi against which various nitro heterocycles are already registered for use.

A new class of nifuroxazide analogues: Synthesis of 5-nitrothiophene derivatives with antimicrobial activity against multidrug-resistant Staphylococcus aureus

Hospital-acquired methicillin-resistant Staphylococcus aureus (MRSA) has been an increasing problem worldwide since the initial reports over 40 years ago. To examine new drug leads with potential antibacterial activities, 14 p-substituted benzoic acid [(5-nitro-thiophen-2-yl)-methylene]-hydrazides were designed, synthesized, and tested against standard and multidrug-resistant S. aureus strains by serial dilution tests. All compounds exhibited significant bacteriostatic activity and some of them also showed bactericidal activity. The results confirmed the potential of this class of compounds as an alternative for the development of selective antimicrobial agents.

In vitro activity and mechanism of action against the protozoan parasite Trypanosoma cruzi of 5-nitrofuryl containing thiosemicarbazones

The in vitro growth inhibition activity of new thiosemicarbazone derivatives against the protozoan parasite Trypanosoma cruzi, the causative agent of American trypanosomiasis, are described. The designed compounds combine in the same molecule the thiosemicarbazone function, recently described as a potent cruzain-inhibitor moiety, and the recognised 5-nitrofuryl group, an oxidative stress promoter. Some of the derivatives were found to be very active against the cultured (epimastigote) form of the parasite, being 1.5-1.7-fold more active than the reference compound, Nifurtimox. Free radicals production was detected when the compounds were incubated in presence of mammalian-liver microsomes. The thiosemicarbazones' capacity to act as pharmacophore in the cruzain inhibition process was theoretically analysed. Frontier molecular orbital HOMO was found as an adequate descriptor in this process. Acute in vivo toxicity of two of the more active derivatives was evaluated. The results showed that these compounds are among the most potent 5-nitrofuryl derivatives tested against this parasite thus support further in vivo studies of some of these thiosemicarbazones.

Small molecules with antimicrobial activity against E. coli and P. aeruginosa identified by high-throughput screening

BACKGROUND AND PURPOSE

New antimicrobials are needed because of the emergence of organisms that are resistant to available antimicrobials. The purpose of this study was to evaluate a high-throughput screening approach to identify antibacterials against two common disease-causing bacteria, and to determine the frequency, novelty, and potency of compounds with antibacterial activity.

EXPERIMENTAL APPROACH

A high-throughput, turbidometric assay of bacterial growth in a 96-well plate format was used to screen a diverse collection of 150,000 small molecules for antibacterial activity against E. coli and P. aeruginosa. The statistical Z'-factor for the assay was > or = 0.7.

KEY RESULTS

Screening for inhibition of E. coli growth gave a 'hit' rate (> 60% inhibition at 12.5 microM) of 0.025%, which was more than 5-fold reduced for P. aeruginosa. The most potent antibacterials (EC50 < 0.5 microM) were of the nitrofuran class followed by naphthalimide, salicylanilide, bipyridinium and quinoazolinediamine chemical classes. Screening of > 250 analogs of the most potent antibacterial classes established structure-activity data sets.

CONCLUSIONS AND IMPLICATIONS

Our results validate and demonstrate the utility of a growth-based phenotype screen for rapid identification of small-molecule antibacterials. The favourable efficacy and structure-activity data for several of the antibacterial classes suggests their potential development for clinical use.

Small-Molecule NSC59984 Restores p53 Pathway Signaling and Antitumor Effects against Colorectal Cancer via p73 Activation and Degradation of Mutant p53

The tumor-suppressor p53 prevents cancer development via initiating cell-cycle arrest, cell death, repair, or antiangiogenesis processes. Over 50% of human cancers harbor cancer-causing mutant p53. p53 mutations not only abrogate its tumor-suppressor function, but also endow mutant p53 with a gain of function (GOF), creating a proto-oncogene that contributes to tumorigenesis, tumor progression, and chemo- or radiotherapy resistance. Thus, targeting mutant p53 to restore a wild-type p53 signaling pathway provides an attractive strategy for cancer therapy. We demonstrate that small-molecule NSC59984 not only restores wild-type p53 signaling, but also depletes mutant p53 GOF. NSC59984 induces mutant p53 protein degradation via MDM2 and the ubiquitin-proteasome pathway. NSC59984 restores wild-type p53 signaling via p73 activation, specifically in mutant p53-expressing colorectal cancer cells. At therapeutic doses, NSC59984 induces p73-dependent cell death in cancer cells with minimal genotoxicity and without evident toxicity toward normal cells. NSC59984 synergizes with CPT11 to induce cell death in mutant p53-expressing colorectal cancer cells and inhibits mutant p53-associated colon tumor xenograft growth in a p73-dependent manner in vivo. We hypothesize that specific targeting of mutant p53 may be essential for anticancer strategies that involve the stimulation of p73 in order to efficiently restore tumor suppression. Taken together, our data identify NSC59984 as a promising lead compound for anticancer therapy that acts by targeting GOF-mutant p53 and stimulates p73 to restore the p53 pathway signaling.

Multi-residue monitoring for the simultaneous determination of five nitrofurans (furazolidone, furaltadone, nitrofurazone, nitrofurantoine, nifursol) in poultry muscle tissue through the detection of their five major metabolites (AOZ, AMOZ, SEM, AHD, DNSAH) by liquid chromatography coupled to electrospray tandem mass spectrometry—In-house validation in line with Commission Decision 657/2002/EC

Following the ban of four nitrofurans in the mid-90s (furazolidone, furaltadone, nitrofurantoine, nitrofurazone), the nifursol, a veterinary drug from the nitrofuran class of antibacterials which has been used prophylactically as feed additive for treating turkeys against histomoniasis (blackhead disease) was also declared in Annex IV of the European Union Directive no. 90/2377/EC in 2002 according to the Regulation no. 1756/2002/EC. As for the four other nitrofurans, nifursol disappears from tissues within a few days after treatment of food-producing animals. But toxic metabolites are still present for longer periods (several weeks or even months). The major metabolite that can readily be monitored in the tissues following nifursol abuse is the 3,5-dinitro-salicylic acid hydrazine (DNSAH). This article displays some improvements and the revalidation of the analytical method by liquid chromatography coupled to electrospray tandem mass spectrometry (LC-esiMS/MS) already in use in our laboratory for monitoring nitrofuran metabolites but also including the nifursol metabolite at the confirmatory minimum required performance level (MRPL) of 1 microg kg(-1). The validation is applied both to artificially and to naturally incurred turkey muscle.

Aquatic photochemistry of nitrofuran antibiotics

The aquatic photochemical degradation of a class of pharmaceuticals known as the nitrofuran antibiotics (furaltadone, furazolidone, and nitrofurantoin) was investigated. Direct photolysis is the dominant photodegradation pathway for these compounds with the formation of a photostationary state between the syn and the anti isomers occurring during the first minutes of photolysis. The direct photolysis rate constant and quantum yield were calculated for each of the three nitrofurans. Reaction rate constants with reactive oxygen species (ROS), 102 and *OH, were also measured, and half-lives were calculated using environmentally relevant ROS concentrations. Half-lives calculated for reaction with 1O2 and *OH are in the ranges of 120-1900 and 74-82 h, respectively. When compared to the direct photolysis half-lives, 0.080-0.44 h in mid-summer at 45 degrees N latitude, it is clear that indirect photochemical processes cannot compete with direct photolysis. The major photodegradation product of the nitrofurans was found to be nitrofuraldehyde, which is also photolabile. Upon photolysis, nitrofuraldehyde produces NO, which is easily oxidized to nitrous acid. The acid produced further catalyzes the photodegradation of the parent nitrofuran antibiotics, leading to autocatalytic behavior. Natural waters were found to buffer the acid formation.

Resistance to the nitroheterocyclic drugs

The nitroheterocyclic drugs have been available since the early 1960's for the treatment of anaerobic protozoa. The application of these drugs has widened since then and they are presently used to treat anaerobic pathogenic bacteria and protozoa. The activity of the nitroheterocyclic drugs depends on the all-important nitro group attached to the imidazole or furan ring. Although the nitro radicals, generated by reduction of the parent drugs, are similar for both families of nitroheterocyclics, the nitroimidazoles and the nitrofurans, the electron potential of each is different and thus the mechanism of action depends on different pathways. The nitroimidazoles depend on reduction by ferredoxin or flavodoxin. The nitrofurans require nitroreductase activity, but the natural substrate of these enzymes has not been identified. Increased use of nitroheterocyclic drugs, in response to drug resistance to other commonly used antibiotics, has in turn resulted in drug resistance to a number of nitroheterocyclic drugs. Bacteroides strains and other bacteria, including Helicobacter, have developed resistance. Among the protozoa, Trichomonas has developed resistance to metronidazole via a number of mechanisms, especially a decrease in drug reduction, as a result of alterations in the electron transport pathways. Resistance to both types of nitroheterocyclic drugs has been reported in Giardia. Although resistance to these drugs is not widespread, their increased use world-wide as a prophylaxis and in chemotherapy will inevitably result in increased resistance in organisms commonly found in asymptomatic infections, including Trichomonas, Giardia and Entamoeba. However, the variety of substitutions which can be attached to the ring structures has led to a great variety of drugs being synthesised, some of which are many-fold more active than the commonly prescribed nitroheterocyclics. With careful administration of currently available drugs and continued interest in synthesising more active compounds, we can optimistically expect to have useful nitroheterocyclic drugs available for some time.

Nitrofuran drugs as common subversive substrates of Trypanosoma cruzi lipoamide dehydrogenase and trypanothione reductase

Lipoamide dehydrogenase (LipDH), trypanothione reductase (TR), and glutathione reductase (GR) catalyze the NAD(P)H-dependent reduction of disulfide substrates. TR occurs exclusively in trypanosomatids which lack a GR. Besides their physiological reactions, the flavoenzymes catalyze the single-electron reduction of nitrofurans with the concomitant generation of superoxide anions. Here, we report on the interaction of clinically used antimicrobial nitrofurans with LipDH and TR from Trypanosoma cruzi, the causative agent of Chagas' disease (South American trypanosomiasis), in comparison to mammalian LipDH and GR. The compounds were studied as inhibitors and as subversive substrates of the enzymes. None of the nitrofurans inhibited LipDH, although they did interfere with the disulfide reduction of TR and GR. When the compounds were studied as substrates, T. cruzi LipDH showed a high rate of nitrofuran reduction and was even more efficient than its mammalian counterpart. Several derivatives were also effective subversive substrates of TR, but the respective reaction with human GR was negligible. Nifuroxazide, nifuroxime, and nifurprazine proved to be the most promising derivatives since they were redox-cycled by both T. cruzi LipDH and TR and had pronounced antiparasitic effects in cultures of T. cruzi and Trypanosoma brucei. The results suggest that those nitrofuran derivatives which interact with both parasite flavoenzymes should be revisited as trypanocidal drugs.

Mechanistic interpretation of the genotoxicity of nitrofurans (antibacterial agents) using quantitative structure-activity relationships and comparative molecular field analysis

Quantitative structure-activity relationship (QSAR) and comparative molecular field analysis (CoMFA) have been applied to elucidate the mechanisms of genotoxicity (SOSIP) of nitrofuran derivatives on Escherichia coli PQ37. The following equation was developed: log SOSIP = -33.1qc2 + 1.00 log P - 1.50Isat - 1.19MR - 0.76I5,6 - 3.76; n = 40, r = 0.900, s = 0.475. The QSAR model clearly reveals three important factors, namely, electronic (qc2), hydrophobic (log P) and steric (MR, Isat, I5,6) contributing toward the genotoxic activity of this class of compounds. qc2, the charge on the c2 atom attached to the NO2 group, supports a furan ring opening mechanism in explaining the genotoxicity. The finding of the coefficient of 1 with log P conforms to our previous findings with several different classes of mutagens acting on different systems. CoMFA analysis clearly demonstrates its potential in unraveling the steric features of the molecules through contour maps. The CoMFA cross-validated model also supports the importance of the electronic factor. It could not reveal any hydrophobic influence because the interaction energies of the CH3 and H2O probes are collinear. QSAR (classical) and CoMFA, if used judiciously, may complement each other and enhance the applicability of SAR in drug design.

Novel bidentate complexes of Cu(II) derived from 5-nitrofuran-2-carboxaldehyde thiosemicarbazones with antiamoebic activity against E. histolytica

The novel analogues of 5-nitrofuran-2-carboxaldehyde thiosemicarbazones 1-10 were synthesized and their copper(II) complexes 1a-10a were obtained by means of coordination with cupric chloride. All these compounds have been characterized by elemental analysis, IR, electronic spectra and thermogravimetric patterns while ligands have also been characterized by 1H NMR spectral studies. These copper complexes are bidentate and possess octahedral geometry around Cu(II) ion. Their antiamoebic activities were carried out to ascertain their effectiveness in comparison to their corresponding thiosemicarbazones. A number of these complexes possess noteworthy potencies towards HK-9 strain of Entamoeba histolytica in vitro. The complexes 2a-7a, 9a and 10a showed less IC50 value than metronidazole, the drug of choice for amoebiasis. Moreover, complexes 2a and 9a have shown the most promising antiamoebic activities (IC50 = 0.38 microM of 2a and IC50 = 0.34 microM of 9a versus IC50 = 1.81 microM of metronidazole). These results indicate that the metallated thiosemicarbazone may be lead molecule to inhibit growth of E. histolytica.

Investigation of 5-nitrofuran derivatives: synthesis, antibacterial activity, and quantitative structure-activity relationships

Three sets of antibacterial nitrofuran derivatives [set I, 5-R-substituted (Z)-2-(5-nitrofuran-2-ylmethylene)-3(2H)-benzofuranones (R = OCH(3), H, CH(3), C(2)H(5), nC(3)H(7), Cl, Br, CN, and NO(2)) and their 2-hydroxyphenyl and 2-acetoxyphenyl analogues; set II, 5-R-substituted (E)-1-(2-hydroxyphenyl)-3-(5-nitrofuryl)-2-propen-1-ones (R = H, CH(3), C(2)H(5), Cl, and NO(2)); and set III, 5-R-substituted (E)-1-(2-acetoxyphenyl)-3-(5-nitrofuryl)-2-propen-1-ones (R = H, CH(3); C(2)H(5), Cl, and NO(2))] were prepared and tested against a Gram-positive (Staphylococcus aureus, strain ATCC-25923) and a Gram-negative bacterium (Caulobacter crescentus, strain NA 1000). QSAR equations derived for the IC(50) values against both bacteria show negative contributions of two terms: an electronic one, expressed either by sigma, the Hammett substituent constant, or by E, the cyclic voltametric reduction potential. Another term described by an indicator variable, I(abs), is assigned the value of 0 for set I compounds and the value of 1 for sets II and III. No important contribution of the hydrophobic factor was found. For the three sets, the QSAR regressions suggest that the same structural features describe the activities for both bacteria and that, although reduction is a necessary step, it should not be the determining one. These results agree with those found for the QSAR of 5-nitroimidazole analogues.

Intramolecular cyclization reactions of 5-halo- and 5-nitro-substituted furans

[reaction: see text] Intramolecular cyclization reactions of 5-halo- and 5-nitro-substituted furanylamides were examined. The 2-alkoxy-5-bromofuran derivative 2 produced the rearranged dihydroquinone 6 (36%), a product from the rearrangement of the intermediate oxabicycle 3. The 5-halo substituted furoyl amide 18 was converted to the polyfunctional oxabicycle 20 in 82% yield and at a much faster rate than the unsubstituted furanyl system 17. The 5-nitro-substituted furfuryl amide 33b underwent an unusual isomerization-cyclization reaction under microwave conditions to provide 1,4-dihydro-2H-benzo[4,5]furo[2,3-c]pyridin-3-one 34.

Broad spectrum detection of veterinary drugs with a highly stable metal-organic framework

The broad spectrum detection of veterinary drugs is very important for rapid and large-scale safe screen of animal-derived foods. Metal-organic frameworks (MOFs), as a kind of emerged functional porous materials are quite promising in the chemical sensing and molecular detection. In this work, we report the high-performance broad spectrum detection of 15 commonly-used veterinary drugs through the fluorescence quenching in a newly-designed chemically stable Al-based MOF, Al₃(μ₃-O)(OH)(H₂O)₂(PPTTA)_3/2 (BUT-22). To the best of our knowledge, this is the first systematic investigation for the application of MOFs in the detection/sensing of veterinary drugs through fluorescence quenching method. The quenching efficiencies of the tested veterinary drugs on BUT-22 are all beyond 82%, and the limits of detection (LOD) are low at parts per billion (ppb) levels. Interestingly, BUT-22 also enables the selective detection of nicarbazin (NIC) through the clearly-observed red shift of its maximum fluorescence emission wavelength. Moreover, the fluorescence quenching mechanism was explored with the help of theoretical calculations. Our work indicates that MOFs are favorable materials for the detection of veterinary drugs, being potentially useful in monitoring drug residues of animal-derived foods.

Antiplasmodial activity of nitroaromatic and quinoidal compounds: redox potential vs. inhibition of erythrocyte glutathione reductase

Prooxidant nitroaromatic and quinoidal compounds possess antimalarial activity, which might be attributed either to their formation of reactive oxygen species or to their inhibition of antioxidant enzyme glutathione reductase (GR, EC 1.6.4.2). We have examined the activity in vitro against Plasmodium falciparum of 24 prooxidant compounds of different structure (nitrobenzenes, nitrofurans, quinones, 1,1'-dibenzyl-4,4'-bipyridinium, and methylene blue), which possess a broad range of single-electron reduction potentials (E(1)(7)) and erythrocyte glutathione reductase inhibition constants (K(i(GR))). For a series of homologous derivatives of 2-(5'-nitrofurylvinyl)quinoline-4-carbonic acid, the relationship between compound K(i(GR)) and concentration causing 50% parasite growth inhibition (IC(50)) was absent. For all the compounds examined in this study, the dependence of IC(50) on their K(i(GR)) was insignificant. In contrast, IC(50) decreased with an increase in E(1)(7) and positive electrostatic charge of aromatic part of molecule (Z): log IC(50) (microM) = -(0.9846 +/- 0.3525) - (7.2850 +/- 1.2340) E(1)(7) (V) - (1.1034 +/- 0.1832) Z (r(2) = 0.8015). The redox cycling activity of nitroaromatic and quinoidal compounds in ferredoxin:NADP(+) reductase-catalyzed reaction and the rate of oxyhemoglobin oxidation in lysed erythrocytes increased with an increase in their E(1)(7) value. Our findings imply that the antiplasmodial activity of nitroaromatic and quinoidal compounds is mainly influenced by their ability to form reactive oxygen species, and much less significantly by the GR inhibition.

Quantitative structure-activity relationship studies on nitrofuranyl anti-tubercular agents

A series of nitrofuranylamide and related aromatic compounds displaying potent activity against Mycobacterium tuberculosis have been investigated utilizing 3-dimensional quantitative structure-activity relationship (3D-QSAR) techniques. Comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) methods were used to produce 3D-QSAR models that correlated the minimum inhibitory concentration (MIC) values against M. tuberculosis with the molecular structures of the active compounds. A training set of 95 active compounds was used to develop the models, which were then evaluated by a series of internal and external cross-validation techniques. A test set of 15 compounds was used for the external validation. Different alignment and ionization rules were investigated as well as the effect of global molecular descriptors including lipophilicity (cLogP, LogD), polar surface area (PSA), and steric bulk (CMR), on model predictivity. Models with greater than 70% predictive ability, as determined by external validation, and high internal validity (cross-validated r(2)>.5) have been developed. Incorporation of lipophilicity descriptors into the models had negligible effects on model predictivity. The models developed will be used to predict the activity of proposed new structures and advance the development of next generation nitrofuranyl and related nitroaromatic anti-tuberculosis agents.

Theoretical evaluation of adiabatic and vertical electron affinity of some radiosensitizers in solution using FEP, ab initio and DFT methods

The biological activity of radiosensitizers is associated to their electron affinity (EA), which can be divided in two main processes: vertical and adiabatic. In this work, we calculated the EAs of nitrofurans and nitroimidazoles (Fig. 2) using Hartree-Fock (HF) and density functional theory (DFT) methods and evaluated solvent effects (water and carbon tetrachloride) on EAs. For water, we combined the polarized continuum model (PCM) and free energy perturbation (FEP) (finite difference thermodynamic integration, FDTI) methods. For carbon tetrachloride, we used the FDTI method. The values of adiabatic EA obtained are in agreement with experimental data (deviations of 0.013 eV). The vertical EAs were calculated according to Cederbaum's outer valence Green function (OVGF) method. This methodology, which relies on theoretical aspects of free energy calculations on charged molecules in solution, was used to select potential selective radiosensitizers from recently reported compounds and could be helpful in the rational design of new and more selective bioreductive anticancer drugs.

Synthesis of novel hybrid molecules from precursors with known antiparasitic activity

Three novel new compounds derived from antiparasitic precursors have been synthesized and tested for their antiamoebic and antigiardial activities. The condensation of 2-(2-methyl-5-1H-nitroimidazolyl)ethylamine (6) with 5-nitro-2-furylacrylic acid (7) gave 3-(5-nitrofuran-2-yl)-N-[2-(5-nitroimidazol-1-yl)ethyl]acrylamide (8). Condensation of 7 with 7-chloro-4-(piperazin-1-yl)quinoline (9) afforded 1-[4-(7-chloroquinolin-4-yl)piperazin-1-yl)-3-(5-nitrofuran-2-yl)propenone as a mixture of two isomers; 10-a (the E-isomer) and 10-b (the Z-isomer). In addition, the reaction of 9 with 1-(2-bromoethyl)-2-methyl-5-nitroimidazole (11) in the presence of K2CO3 and NaI yielded 7-chloro-4-(4-[2-(5-nitroimidazol-1-yl)ethyl]-piprazin-1-yl)quinoline (12). On the basis of preliminary screening data for these new compounds, compound 12 exhibited potent lethal activities against Entamoeba histolytica and Giardia intestinalis; its IC₅₀ ( about 1 µM) was lower, at least by a factor of five, compared to the standard drug, metronidazole. In addition, the IC₅₀ of compound 12 against the tested parasites is 600 times below that against Hep-2 and Vero cells. Compounds 8 and 10-a also exhibited potent or moderate antiamoebic and antigiardial activities with IC_{50 values} of about 5.5 µM, and 140 µM, respectively, against the tested parasites. These two hybrid molecules, 8, 10-a, were also non-cytotoxic at the lethal concentrations against the parasites.

Nitrofurylsemicarbazone Rhenium and Ruthenium Complexes as Anti-trypanosomal Agents

Rhenium and ruthenium complexes of the type [Re(V)OCl(2)(PPh(3))L] and [Ru(II)Cl(2)(DMSO)(2)L], where L are 5-nitrofurylsemicarbazone derivatives, were prepared in an effort to obtain new anti-trypanosomal agents combining the recognized biological activity of these metals and the trypanocidal activity of the free ligands. Rhenium complexes resulted unstable in aqueous solution not allowing their use as potential drugs. On the other hand, complexation to ruthenium of the bioactive ligands lead to the lack of antiprotozoa activity even though free radical production and redox cycling induction were detected when the compounds were incubated in presence of Trypanosoma cruzi cells. The lack of anti-trypanosomal activity of ruthenium complexes could be explained on the basis of their high protein binding capacity and their high hydrophilicity.

Validation of a confirmatory method for the determination of residues of four nitrofurans in egg by liquid chromatography–tandem mass spectrometry with the software InterVal

A method for the detection and determination of nitrofuran derivatives in egg by liquid chromatography-tandem mass spectrometry (LC-MS/MS) was validated with the software InterVal and can be applied for the confirmation of nitrofuran metabolites in fresh or lyophilised eggs. The validation study comprises variations in operator, storage condition, breeding, equipment and duration of sample preparation. A comprehensive overview of the robustness of the method is obtained by analysing eight samples at six concentration levels. First results of short- and medium-term investigations for stability of analytes in solution show that standard solutions of nitrofuran metabolites are stable for at least 1 year when stored at +4 degrees C in the dark. The decision limit CCalpha expressed for the underivatised metabolite is 0.05 microg kg(-1) for 3-amino-5-methyl-morpholino-2-oxazolidinone, 0.03 microg kg(-1) for 3-amino-2-oxazolidinone, 0.20 microg kg(-1) for semicarbazide and 0.22 microg kg(-1) for 1-amino-hydantoin.

Advantages of LC–MS–MS compared to LC–MS for the determination of nitrofuran residues in honey

In the framework of developing analyses for exogenous contaminants in food matrices such as honey, we have compared data obtained by high-performance liquid chromatography coupled with mass spectrometry (LC-MS) to those provided by high-performance liquid chromatography and tandem mass spectrometry (LC-MS-MS). Initial results obtained with LC-MS showed that the technique lacked selectivity, which is why the method was validated by LC-MS-MS. This method involves a solid-phase extraction (SPE) of nitrofuran metabolites and nitrofuran parent drugs, a derivatization by 2-nitrobenzaldehyde for 17 h, and finally a clean-up by SPE. The data obtained show that the limits of detection varied between 0.2 and 0.6 microg kg(-1) for the metabolites and between 1 and 2 microg kg(-1) for nitrofuran parent drugs. The method was applied to different flower honeys. The results showed that nitrofurans (used as antibiotics) are consistently present in this matrix, the predominant compound being furazolidone. Figure Working bees.

The interaction of nitroaromatic drugs with aminothiols

The effect of cysteamine and glutathione addition on the redox behaviour of metronidazole, chloramphenicol, M&B 4998, nitrofurazone, and nifuroxime has been studied by electrochemical techniques. The presence of thiol influences the redox behaviour of the nitro compound in a number of ways. In aqueous media, the single-step nitro/hydroxylamine reduction shows a decrease in current and a shift to more positive potentials, which is assigned to the thiol acting as the reducing agent, but only after the formation of the nitro radical anion. In addition, the reversible RNO/RNHOH couple is greatly diminished or removed. In a dimethylformamide/H2O solvent, the nitro radical anion can be selectively generated. The effect of thiol addition on the stability of the radical anion is strongly dependent on the drug, the identity of the thiol, and the concentration of the supporting electrolyte. The presence of thiol can result in an increase or a decrease in the lifetime of the radical with no apparent correlation with the redox couple of the nitro compound, or can act as an oxidizing agent and regenerate the original nitro compound. These disparate routes by which thiol can modify the redox characteristics of nitro compounds suggest that the traditional role of thiol as a radical scavenger needs to be extended.

Redox behaviour of nifuroxazide: generation of the one-electron reduction product

The electrochemical properties of nifuroxazide have been investigated in aqueous and aqueous-DMF mixed solvents. In aqueous media, a single, irreversible four-electron reduction occurs to give the hydroxylamine derivative. In mixed media, a reversible one-electron reduction to form a nitro radical anion takes place. Cyclic voltammetric studies show that the anion radical product is stable, although the nitro radical anion intermediate shows a tendency to undergo further chemical reactions. A comparison with the voltammetric behaviour of other nitrofurans such as nifurtimox, nitrofurazone and furazolidone is made. The electrochemically-obtained parameters are correlated with the in vivo studies of oxygen consumption on Trypanosoma cruzi cell suspensions.