Design, synthesis, molecular modeling, in vitro evaluation of novel piperidine-containing hydrazone derivatives as cholinesterase inhibitors.

In an effort to develop new and effective therapeutic agents for Alzheimer's disease, a series of hydrazone derivatives bearing piperidine rings have been designed and synthesized. The chemical structures of the compounds were characterized by various spectroscopic techniques. In vitro antioxidant and cholinesterase activities of the compounds were evaluated. Among the compounds, N12 exhibited the most antioxidant activity in all methods (CUPRAC, FRAP, DPPH, ABTS). In vitro acetylcholinesterase (AChE) activity results of the compounds showed good IC50 values between 14.124 ± 0.084 and 49.680 ± 0.110 µM were obtained (IC50 = 38.842 ± 0.053 µM for Donepezil). Among the compounds, N7 and N6 are much more effective derivatives than the standard compound donepezil with IC50 values of 14.124 ± 0.084 and 17.968 ± 0.072 µM, respectively. In vitro, butyrylcholinesterase (BChE) inhibition values of the compounds were between 13.505 ± 0.025 and 52.230 ± 0.027 µm. Among the compounds, N6 has the highest BChE inhibition with an IC50 value of 13.505 µm in the series. The cytotoxicity and AChE inhibitory activity of the compounds on SH-SY5Y cell lines were also evaluated. Kinetic studies were also performed to determine the behavior of the compounds as competitive or noncompetitive inhibitors. The binding modes of N6, which was determined to be highly effective according to in vitro analyses, with AChE and BChE were investigated using molecular docking studies, and the stability of the complexes was determined by molecular dynamics simulations. These findings indicated that AChE and BChE enzymes maintained their overall structural stability and compactness during interactions with compound N6.

Synthesis, Biological Evaluation and in Silico Studies of New Pyrazoline Derivatives Bearing Benzo[d]thiazol-2(3H)-one Moiety as Potential Urease Inhibitors.

Novel pyrazoline derivatives containing benzo[d]thiazol-2(3H)-one moiety were synthesized and screened for their inhibitory properties against urease, a clinically important metabolic enzyme. In vitro enzyme inhibition studies revealed that all pyrazolines (7.21-87.77 µM) were more potent than the standard inhibitor acetohydroxamic acid (251.74 µM) against the urease enzyme. Most notably, compound 2m, which is more active than the other compounds in vitro and molecular docking studies, showed a significant inhibition potential and efficient IC50 values (7.21±0.09 µM) and in silico inhibition constant (0.11 µM). Furthermore, molecular dynamics (MD) simulation analysis suggests that the binding stability of urease enzyme and compound 2m were stably maintained during the 100 ns simulation time. Compound 2m also exhibited good physicochemical and pharmacokinetic parameters. The overall results of urease inhibition have indicated that these pyrazoline derivative compounds can be further optimized and developed for the discovery of novel urease inhibitors.

N-Substituted Arylidene-3-(Methylsulfonyl)-2-Oxoimidazolidine-1-Carbohydrazide as Cholinesterase Inhibitors: Design, Synthesis, and Molecular Docking Study.

The development of new enzyme inhibitors in degenerative brain diseases has gained more attention. Enzyme inhibitors play an effective role in controlling central nervous system diseases. For this purpose, a novel series of hydrazone derivatives containing imidazolidine ring aimed against Alzheimer's disease (AD), have been designed and synthesized. The acetylcholinesterase (AChE) enzyme inhibitory activity of these compounds was investigated. The structures of the compounds were determined by IR, 1 H and 13 C-NMR and mass spectroscopic methods. Inhibition studies on the cholinesterase (ChE) enzymes and ß-amyloid plaque inhibition test of the compounds were performed. Based on the experimental results, compound 3j bearing dimethoxy substituent on the aromatic ring like donepezil exhibited the most AChE inhibitory activity with the IC50 values of 0.023±0.001 µM. Owing to obtained biological activity and molecular docking study results, it is thought that the most active compound 3j may play a role in both symptomatic and palliative treatment of AD.

Novel 2,5-disubstituted-1,3,4-oxadiazole derivatives as MAO-B inhibitors: Synthesis, biological evaluation and molecular modeling studies.

Thirty novel 2,5-disubstituted-1,3,4-oxadiazole derivatives bearing urea moiety were designed and synthesized. IR, 1H-NMR, 13C-NMR and mass spectroscopic methods and elemental analysis were used to confirm the structures of the compounds. Their monoamine oxidase inhibitory activity was determined against the MAO-A and MAO-B isoforms. None of the compounds showed the potent MAO-A inhibitory activity, while the MAO-B inhibition was significantly found in the range of 62 to 98%. Among them, the compounds H8, H9 and H12 bearing chloro substituent at the fourth position of phenylurea were found to show potent monoamine oxidase B inhibitory activity with IC50 values 0.039-0.066 µM. To define and evaluate the interaction mechanism between compound H8 and monoamine oxidase B, molecular docking studies have been made.

Synthesis of new hydrazone derivatives and evaluation of their monoamine oxidase inhibitory activity.

A novel series of hydrazone derivatives were designed and synthesized. Their structures were characterized by IR, 1H NMR, 13C NMR and HR-MS spectroscopic methods. The newly synthesized compounds were evaluated for their inhibitory activity against monoamine oxidase enzymes (MAO-A and MAO-B). Compounds 2a, 2k, 4a and 4i showed significant inhibitory activity against MAO-A, with IC50 value in the range of 0.084-0.207 µM compared to reference drug moclobemide (IC50 value = 6.061 µM). These compounds (2a, 2k, 4a and 4i) were exposed to cytotoxicity tests to establish their preliminary toxicological profiles and were found to be non-cytotoxic. Moreover, the most effective compound 4i was evaluated using enzyme kinetics and docking studies to elucidate the plausible mechanisms of inhibition of MAO-A. According to enzyme kinetic studies, compound 4i was a reversible and competitive inhibitor with similar inhibition features as the substrates. Also, it was seen that this compound was settled down very properly at the active site of MAO-A enzyme by doing important interactions owing to the docking studies. Finally, ADME predictions were applied to estimate pharmacokinetic profiles of synthesized compounds. According to calculated ADME predictions, all parameters of the compounds were within the standard ranges in terms of "Rule of Five" and "Rule of Three" and it was detected that the synthesized compounds (2a-4i) have good and promising pharmacokinetic profiles.

Design, synthesis and biological evaluation of some new 2-Pyrazoline derivatives as potential anticancer agents.

A new series of N-(4-(1-Phenyl-5-aryl-4,5-dihydro-1H-pyrazol-3-yl)phenyl)-4-substitutedbenzamide derivatives were designed and synthesized from new chalcone derivatives. All newly synthesized compounds were determined by using IR, 1H-NMR, 13C-NMR spectroscopic methods, elemental analysis and evaluated for their in vitro antiproliferative activities on HeLa, MCF-7, MKN-45 cancer cell lines and NIH-3T3 cell line using MTT assay. Expression of Bax and Bcl-2 proteins was detected by Western-blot analysis and caspase-3 enzyme activity was measured. Notably, compounds 1f and 2f showed a significant cytotoxic effect in all three cancer cells and did not display cytotoxicity on NIH-3T3 normal cells. (IC50 = 26.66 ± 2.73 µM on HeLa, IC50 = 9.41 ± 2.19 µM on MCF-7, IC50 = 5.17 ± 3.54 µM on MKN-45 for 1f. IC50 = 17.96 ± 3.34 µM on HeLa, IC50 = 0.69 ± 0.13 µM on MCF-7, IC50 = 0.88 ± 0.16 µM on MKN-45 for 2f.) Moreover, 1f and 2f upregulated protein expression level of Bax and downregulated protein expression level of Bcl-2 in cells. Similarly, caspase-3 activity was increased in cells via 1f and 2f. It can be concluded that 1f and 2f activated apoptosis by inducing mitochondrial apoptotic proteins in HeLa, MCF-7, MKN-45. This could be potentially new anti-cancer derivatives and used to contribute to new therapeutic development.

Synthesis and biological evaluation of new pyrazolone Schiff bases as monoamine oxidase and cholinesterase inhibitors.

In the current work, Schiff base derivatives of antipyrine were synthesized. The chemical characterization of the compounds was confirmed using IR, 1H NMR, 13C NMR and mass spectroscopies. The inhibitory potency of synthesized compounds was investigated towards acetylcholinesterase (AChE), butyrylcholinesterase (BuChE), and monoamine oxidases A and B (MAO-A and MAO-B) enzymes. Some of the compounds displayed significant inhibitory activity against AChE and MAO-B enzymes, respectively. According to AChE enzyme inhibition assay, compounds 3e and 3g were found as the most potent derivatives with IC50 values of 0.285 µM and 0.057 µM, respectively. Also, compounds 3a (IC50 = 0.114 µM), 3h (IC50 = 0.049 µM), and 3i (IC50 = 0.054 µM) were the most active derivatives against MAO-B enzyme activity. So as to understand inhibition type, enzyme kinetics studies were carried out. Furthermore, molecular docking studies were performed to define and evaluate the interaction mechanism between compounds 3g and 3h and related enzymes. ADME (Absorption, Distribution, Metabolism, and Excretion) and BBB (Blood, Brain, Barier) permeability predictions were applied to estimate pharmacokinetic profiles of synthesized compounds.

Design and evaluation of biological activities of 1,3-oxazolidinone derivatives bearing amide, sulfonamide, and thiourea moieties.

1,3-Oxazolidine-2-one is an important heterocyclic ring participating in the chemical structure of many drugs. In this research, 22 new amide/sulfonamide/thiourea derivatives (1-22) were obtained by the reaction of (S)-4-(4-aminobenzyl)-2(1H)-1,3-oxazolidinone with 4-substituted benzoyl chlorides, 4-substituted benzene sulfonyl chlorides, and 4-substituted phenyl isothiocyanates. The structures of all synthesized compounds were clarified by FT-IR, NMR, and mass spectroscopic and elemental analysis techniques. The synthesized compounds were screened for their antimicrobial activity. Antimicrobial susceptibility and cellular physiology were evaluated using the microbroth dilution assay and the flow cytometry method. As a result, it was determined that compound 16 displayed better antimicrobial activity than chloramphenicol against Gram-positive bacteria, especially Staphylococcus aureus. In order to understand the mechanism of effect of the compounds on the cell membrane, fluorescence microscopy was used. Cell membrane damage of the Gram positive bacteria treated with compound 16 was observed as a result of intense staining with propidium iodide. In addition, genotoxicity, cytotoxicity, and absorption, distribution, metabolism, and excretion (ADME) parameters of compound 16 were examined and it was found as non-mutagenic and non-cytotoxic at the concentration at which it showed antimicrobial activity. According to the calculated ADME parameters and drug likeness scores, the compounds can be good drug candidates, especially compound 16.

Insecticidal effect of new synthesized chalcone derivatives on Caribbean fruit fly, Anastrepha suspensa.

In this present study, new chalcone derivatives were synthesized from 4-aminoacetophenone, which were confirmed by spectroscopic methods. The toxic risks of chalcones to humans and the environment were investigated by a web-based platform called ADMETlab. With this program, the possible toxic effects of the compounds on liver, respiratory system, and eyes were evaluated. For the topical insecticidal activity, adult female Caribbean fruit fly, Anastrepha suspensa, was targeted. Results of the toxicity tests showed that chalcone derivatives are effective against female A. suspensa. Among the synthesized chalcones, 1-(4-cinnamoylphenyl)-3-(p-tolyl)urea (2) exhibited the greatest insecticidal activity, resulting in 73 % mortality at 100 µg/fly after 24 h, whereas other derivatives showed less than 30 % mortality. Our results demonstrate that insecticidal activity may be modulated by the presence of a certain phenyl ring in the structure of derivative 2 and, therefore, has potential for design of efficient chemicals for tephritid fruit fly management.

Synthesis and biological activity of substituted urea and thiourea derivatives containing 1,2,4-triazole moieties.

A series of novel thiourea and urea derivatives containing 1,2,4-triazole moieties were synthesized and evaluated for their antifungal and larvicidal activity. Triazole derivatives 3a-e and 4a-e were synthesized by reacting thiocarbohydrazide with thiourea and urea compounds 1a-e and 2a-e, respectively, in a 130-140 °C oil bath. The proposed structures of all the synthesized compounds were confirmed using elemental analysis, UV, IR, 1H-NMR and mass spectroscopy. All compounds were evaluated for antifungal activity against plant pathogens, larvicidal and biting deterrent activity against the mosquito Aedes aegypti L. and in vitro cytotoxicity and anti-inflammatory activity against some human cell lines. Phomopis species were the most sensitive fungi to these compounds. Compounds 1b, 1c, 3a and 4e demonstrated selectively good activity against Phomopis obscurans and only 1b and 4e showed a similar level of activity against P. viticola. Compound 3d, with a LD50 value of 67.9 ppm, followed by 1c (LD50 = 118.8 ppm) and 3e (LD50 = 165.6 ppm), showed the highest toxicity against Aedes aegypti larvae. Four of these compounds showed biting deterrent activity greater than solvent control, with the highest activity being seen for 1c, with a proportion not biting (PNB) value of 0.75, followed by 1e, 2b and 1a. No cytotoxicity was observed against the tested human cancer cell lines. No anti-inflammatory activity was observed against NF-kB dependent transcription induced by phorbol myristate acetate (PMA) in human chondrosarcoma cells.

Synthesis of Phthalimide Derivatives and Their Insecticidal Activity against Caribbean Fruit Fly, Anastrepha suspensa (Loew).

In this study, thirteen phthalimide derivatives were designed and synthesized. All synthesized compounds were evaluated to determine their potential for inhibitory activities against females of the Caribbean fruit fly, Anastrepha suspensa (Loew) (Diptera: Tephritidae). These efforts led to the discovery of three compounds 4a, 4c, and 4d with potent insecticidal activity (LD50 range from 0.70 to 1.91 µg/fly). Among these compounds, 4a exhibited the highest inhibitory potency with 0.70 µg/fly. In addition, in silico models indicated that compound 4a is less toxic than phthalimide and other precursors. Therefore, our results suggest that 4a has strong potential as a candidate component for developing a novel environmentally friendly insecticide for control of pest fruit flies.

Design, Synthesis, In Silico ADMET Studies and Anticancer Activity of Some New Pyrazoline and Benzodioxole Derivatives.

A new series of 2-pyrazoline derivatives starting from substituted benzodioxole chalcones were designed and synthesized. IR and 1H NMR spectral data and elemental analysis were used to characterize the structures of the synthesized compounds. The cytotoxic activities on HeLa, MCF-7 cancer cell lines and NIH-3T3 for these compounds were tested by using MTT assay. Among the synthesized compounds 2d, 2j, 3j and 3n against MCF-7 cells, and 3c against HeLa exhibited significant cytotoxic activity with IC50 between 10.08 and 27.63 µM. Compound 3f showed the most potent anticancer activity against both cancer cells with good selectivity (IC50 = 11.53 µM on HeLa with SI = 81.75 and IC50 = 11.37 µM on MCF-7 with SI = 82.90). Furthermore, in silico ADMET analyses were performed and the drug-likeness properties of the compounds were investigated.

Synthesis and Biological Evaluation of Some Hydrazide-Hydrazone Derivatives as Anticancer Agents.

In this study, a series of hydrazide-hydrazone derivatives (3a-3u) were synthesized and evaluated for their anticancer activities against prostate cancer cell line (PC-3), breast cancer cell line (MCF-7), colon cancer cell line (HT-29) and human umbilical vein endothelial cells (HUVEC) using MTT assay. In particular, compound 3h having a pyrrole ring was found to be the most potent derivative with IC50 = 1.32, 2.99, 1.71 µM against PC-3, MCF-7, HT-29 cancer cell lines respectively using paclitaxel as a standard compound. Furthermore, compound 3h was subjected to further biological studies such as caspase-3 activity and Annexin-V assay to evaluate their inhibitory potentials. The activity results displayed that compound 3h increased caspase-3 activation and the number of cells to early apoptosis. The additional studies like pharmacokinetics, bioavailability scores and drug-likeness properties were also evaluated. The in silico pharmacokinetics predictions displayed that the bioavailability of these compounds may be high.

Induction of Divergent Cell Death Pathways by Urea and Carbohydrazide Derivatives.

BACKGROUND: The complexity of cancer biology and the development of chemotherapy resistance are two main obstacles to cancer treatment and necessitate novel anticancer molecules that target different cell death pathways. Modulation of Endoplasmic Reticulum (ER) stress and subsequent activation of the Unfolded Protein Response (UPR) has been proposed as a potential chemotherapeutic target, as prolonged ER stress can lead to cell death via apoptosis or necrosis. OBJECTIVE: The present study aims to evaluate the molecular mechanism underlying the cytotoxic activity of selected urea and carbohydrazide derivatives. METHODS: Cell proliferation assays were performed on HeLa, Capan-1, MCF-7, HCC-1937, and MRC-5 cell lines by WST-1 assay. The expression levels of selected ER stress, autophagy, and apoptosis marker proteins were compared by immunoblotting to characterize the underlying mechanism of cytotoxicity. Flow cytometry was used to detect apoptosis. RESULTS: Of the tested cytotoxic compounds, 3a, 4a, 5a, 6a, and 1b dramatically and 5b moderately increased ER stress-related CHOP protein levels. Interestingly, 5b but not 3a, 4a, 5a, 6a, or 1b increased the expression of proapoptotic proteins such as cleaved PARP-1 and cleaved caspase-3 and -7. The flow-cytometry analysis further confirmed that the cytotoxic activity of 5b but not the other compounds is mediated by apoptosis, demonstrated by a significant increase in the percentage of late apoptotic cells (7-AAD/annexin V double-positive cells). CONCLUSION: Our results suggest that changing a substituent from trifluoromethyl to nitro in urea and carbohydrazide core structure alters the cell death mechanism from apoptosis to an apoptosis-independent cell death pathway. This study shows an example of how such simple modifications of a core chemical structure could cause the induction of divergent cell death pathways.

Synthesis and anticonvulsant activity of new N-(alkyl/sub-stituted aryl)-N'-[4-(5-cyclohexylamino)-1,3,4-thiadiazole-2-yl)phenyl]thioureas.

A series of novel thiourea derivatives carrying the 5-cylohexylamino-1,3,4-thiadiazole moiety was synthesized and their anticonvulsant activity was evaluated. Structures of the synthesized compounds have been confirmed by IR, 1H-NMR, and elemental analysis. All of the compounds were administered at a dose of 50 mg/kg. Some of the active compounds have different effects in pentylenetetrazole (PTZ) and maximal electroshock (MES) tests, indicating the therapeutical potential in petit mal seizures, but not in grand mal seizures. Compounds 10, 11, 13, and 14 carrying 2-methylphenyl, 4-chlorophenyl, allyl, and 4-methylphenyl on the thiourea pharmacophore, increased the survival rate in the PTZ model. The ED50 values of the active compounds 10, 11, 13, and 14 were found 68.42, 43.75, 18.75 and 25 mg/kg, respectively.

Synthesis and antinociceptive-antimicrobial activities of some new amide derivatives of 3,5-di/-and 1,3,5-trimethylpyrazoles.

Some N-(3,5-di-/1,3,5-trimethylpyrazole-4-yl)-4-substitutedbenzamide derivatives were prepared as possible antiociceptive-antimicrobial agents. New amide derivatives (3-12) were synthesized by reacting 4-amino-3,5-di and 1,3,5-trimethylpyrazoles with 4-substitutedbenzoyl chlorides. Hotplate and tail-immersion tests were used for the determination of the antinociceptive activity. Morphine, was used as a standard test drug. All compounds were administered at a dose of 100 mg/kg ip and some of them had significant antinociceptive activity in both tests. Compound 10 (N-(1,3,5-trimethylpyrazole-4-yl)-4-bromobenzamide), was the most active one in both tests among the compounds. The antinociceptive activity of the compounds 10, 11 (N-(1,3,5-trimethylpyrazole-4-yl)-4-chlorobenzamide), and 12 (N-(1,3,5-trimethylpyrazole-4-yl)-4-fluorobenzamide), started at 30 minutes and continued up to 150 minutes in the hotplate test. Also compounds were tested for their in vitro antimicrobial activity, but exhibited weak antibacterial activity.

Design, Synthesis and Evaluation of the Biological Activities of Some New Carbohydrazide and Urea Derivatives.

OBJECTIVES: Urea and carbohydrazide derivatives are important compounds exhibiting cytotoxic activities. In this study, a series of new urea and carbohydrazide derivatives containing an pyridine ring were synthesized and evaluated for cytotoxic activity. MATERIALS AND METHODS: The proposed structures of the synthesized compounds were confirmed using elemental analysis, IR, and 1H-NMR spectroscopic techniques. The cytotoxic potencies of synthesized compounds were determined using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay (MTT) on BRCA mutant-carrying HCC1937 and Capan-1 cell lines, as well as on MCF7, HeLa, and MRC5 cells. RESULTS: 3a, 3b, 3c and 3d showed cytotoxic activity against all cancer cell lines. CONCLUSION: Our data indicate that compounds 3a-d are more selective to cancer cells compared with nontumoral fibroblasts; however, these compounds are not more potent on HR defective cells with BRCA mutants.

Synthesis and structure-activity relationships of carbohydrazides and 1,3,4-oxadiazole derivatives bearing an imidazolidine moiety against the yellow fever and dengue vector, Aedes aegypti.

BACKGROUND: 1,3,4-Oxadiazole and imidazolidine rings are important heterocyclic compounds exhibiting a variety of biological activities. In this study, novel compounds with oxadiazole and imidazolidine rings were synthesized from 3-(methylsulfonyl)-2-oxoimidazolidine-1-carbonyl chloride and screened for insecticidal activities. The proposed structures of the 17 synthesized compounds were confirmed using elemental analysis, infrared (IR), proton nuclear magnetic resonance (1 H-NMR), and mass spectroscopy. RESULTS: None of the compounds showed larvicidal activity at the tested concentrations against first-instar Aedes aegypti larvae. However, nine compounds exhibited promising adulticidal activity, with mortality rates of ≥80% at 5 µg per mosquito. Further dose-response bioassays were undertaken to determine median lethal dose (LD50 ) values. Compounds 1, 2b, 2c, 2d, 2 g, 3b, 3c, 3 g, and 3 h were effective, with typical LD50 values of about 5 - 10 µg per mosquito against female Ae. aegypti. Compounds 2c (bearing a nitro group on the aromatic ring; LD50 = 2.80 ± 0.54 µg per mosquito) and 3 h (double halogen groups at 2,4 position on the phenyl ring; LD50 = 2.80 ± 0.54 µg per mosquito) were the most promising compounds. CONCLUSION: Preliminary mode of action studies failed to show consistent evidence of either neurotoxic or mitochondria-directed effects. Further chemical synthesis within this series may lead to the development of new effective insecticides. © 2017 Society of Chemical Industry.

High pressure liquid chromatographic analysis of in vivo metabolites of N-(substituted phenyl)-N'-(1,3,5-trimethyl pyrazole-4-yl)thioureas in rats.

The aim of this study was to investigate the in vivo metabolism of N-(substituted phenyl)-N'-(1,3,5-trimethylpyrazole-4-yl)thioureas (substrate) as model compounds in rats via HPLC. The substrates, N-(4-fluoro/chlorophenyl)-N'-(1,3,5-trimethylpyrazole-4-yl)thioureas (T2 and T3), and their possible metabolites were synthesized and the structures of the compounds were elucidated both by spectral and elemental analysis. Substrates were dissolved in 5% gum arabic and administered 100 mg/kg intraperitoneally (i.p.) in a volume of 0.1 ml/100 g. Blood samples were withdrawn before and at 30 min, 1, 2, 4, 8, 12 and 24 h post-dose. Chromatographic separation of the substrate and its metabolites was performed using a Hichrom chromasil C18 column (150 mm x 4.6 mm i.d., 5 microm particle size). The optimal composition of the mobile phase was achieved by using different mixtures of pure methanol and water. From the biotransformation of these thiourea compounds, N-dealkylation metabolites N-(4-fluoro/chloro-phenyl)-N'-(3,5-dimethylpyrazole-4-yl)thioureas (TI and T4) were identified together with unchanged substrate (T2 and T3) in the plasma by comparing them to reference standards via HPLC UV/DAD.

HPLC analysis of in vivo metabolites of 4-nitrobenzoic acid [(5-nitro-2-thiopheneyl)methylene]hydrazide in rats.

The in vivo metabolism of 4-nitrobenzoic acid [(5-nitro-2-thiopheneyl)methylene]hydrazide (substrate), a model that represents hydrazide hydrazone compounds, was investigated in the rat. The metabolites were monitored in rat plasma at certain time intervals. The substrate was dissolved in dimethylsulfoxide (DMSO)/water (1:4) and administered intraperitoneally at dose of 100 mg/kg and 500 mg/kg. Blood samples were collected at 30 min, then at 1,2, 4, 8, 12 and 24 h post-administration. The chromatographic separation of the substrate and its metabolites was performed on aNovapak C18 (Phenomenex) (150 mm x 4.6 mm i.d., 5-microm particle size) using a mobile phase consisting of phosphate buffer: acetonitrile (90:10, v/v) with a linear gradient system. From the biotransformation of this compound, 4-nitrobenzoic acid (M3) was identified together with the substrate, as evidenced by high pressure liquid chromatography (HPLC)-UV/diode array detection (DAD).