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PubMed2002

NMR and Bayesian regularized neural network regression for impurity determination of 4-aminophenol.

A method for the determination of 4-aminophenol as an impurity in paracetamol (N-(4-hydroxyphenyl)-acetamide) by proton nuclear magnetic resonance ((1)H-NMR) spectroscopy has been developed. The (13)C-satellite from the protons in the ortho position from the hydroxyl group in paracetamol was used as an internal standard, although these peaks interfered with the peaks from the protons in 4-aminophenol. Because of interference in the spectra and non-linearity over a wide calibration range, a Bayesian regularized neural network model was used for calibration. Various kinds of data preprocessing were examined: zero filling, multiplication by a negative exponential function (line broadening), followed by Fourier transformation of the free induction decay (FID). The NMR spectral data were automatically phased and shift-adjusted by means of a genetic algorithm. Multiplicative scatter correction and data compression by wavelets and sequential zeroing of weights variable selection were performed to obtain an optimal calibration model. Neither zero filling of the FID nor line broadening improved the calibration models with regard to error of prediction, so these processes were excluded in the final model. The generated Bayesian regularized network model was evaluated with an independent test set. Four different models with different test sets were constructed to explore the quality of the calibration. The mean error of the optimal calibration model was 25.3 x 10(-6) weight of 4-aminophenol per weight paracetamol. The method is characterized by being relative fast, simple and sufficient sensitive for typical pharmaceutical impurity determinations.

Acetaminophen↗
PubMed2002

Design and synthesis of aminophenol-based factor Xa inhibitors.

A novel potent and selective aminophenol scaffold for fXa inhibitors was developed from a previously reported benzimidazole-based naphthylamidine template. The aminophenol template is more synthetically accessible than the benzimidazole template, which simplified the introduction of carboxylic acid groups. Substitution of a propenyl-para-hydroxy-benzamidine group on the aminophenol template produced selective, sub-nanomolar fXa inhibitors. The potency of the inhibitors is partially explained with the aid of a trypsin complex crystal structure.

Aminophenols↗
PubMedDate not supplied

Fluorinated o-aminophenol derivatives for measurement of intracellular pH.

The simple 2-aminophenol group which serves as a building block for many cationic indicators has been modified to yield a series of pH sensitive probes. This approach is based on the replacement of one of the N-acetate groups of the chelator APTRA (o-aminophenol N,N,O-triacetate) by an N-ethyl group. The resulting series of (N-ethylamino)phenol (NEAP) compounds exhibit pK values in the physiological range and negligible affinity for physiological levels of other ions. Three fluorinated analogs have been prepared: N-ethyl-5-fluoro-2-aminophenol N,O-diacetate (5F NEAP), N-ethyl-2-((2-fluoro-4-carboxybenzyl)oxy)-4-fluoroaniline-N- acetic acid (5F NEAP-2), and 1-(2-(N-ethylamino)-5-fluorophenoxy)-2-(2-fluoro-4- aminophenoxy)ethane-N,N',N'-triacetic acid (5F NEAP-3). These derivatives exhibit total titration shifts of approximately 11 ppm. NEAP-2 and NEAP-3 contain an additional fluorine to serve as an internal chemical shift reference, and NEAP-3, the most highly charged analog prepared, was designed in order to minimize leakage.

Aminophenols↗
PubMed1978

Product inhibition of o-aminophenol glucuronidation by p-nitrophenyl glucuronide in detergent-treated microsomal fractions.

The glucuronidation of o-aminophenol is unaffected by p-nitrophenyl gluronide when native microsomal fractions are the source of UDP-glucuronyltransferase. When microsomal fractions treated with Lubrol detergent are the source of the enzyme, however, p-nitrophenyl glucuronide exhibits competitive inhibition of o-aminophenol glucuronidation. In addition, the apparent K1 for p-nitrophenyl glucuronide is the same whether o-aminophenol or p-nitrophenol is the acceptor substrate. The data suggest that UDP-glucuronyltransferase has one binding site for the two phenols and that the absence of inhibition observed in native microsomal fractions is dependent on an intact microsomal membrane.

Aminophenols↗
PubMed2004

Reactions of arylamine and aminophenol derivatives, and riboflavin with organic radicals.

Based on product yield data on radiolysis of hexane, ethanol and 3 M aqueous ethylene glycol solutions, the ability of a number of arylamine, aminophenol and quinonimine derivatives to affect processes involving peroxyl, alkyl or alpha-hydroxyalkyl radicals was assessed. It has been shown that the introduction of a hydroxyl group into aromatic amine structure enhances its antioxidant performance and makes it significantly more reactive with respect to carbon-centered organic radicals. Replacement of the hydrogen atom of a hydroxyl group by a methyl group decreases the anti-radical activity of aminophenols drastically. Compounds containing (or capable of forming) a quinonimine moiety interact with alkyl or alpha-hydroxyalkyl radicals most effectively, suppressing recombination and fragmentation reactions of the latter. In the sequence: aromatic amines--aminophenols--quinonimines, a trend towards enhancement of the ability of the compounds studied to react with carbon-centered radicals was noted. Also, this study presents for the first time evidence of riboflavin reactivity with respect to organic radicals.

Alkylation↗
PubMed1992

Synthesis and cytotoxic properties of new N-substituted 4-aminophenol derivatives with a potential as antimelanoma agents.

New tyrosinase-targeted compounds based on structural variants of the prototype unit 4-aminophenol have been synthesized and screened for their potential as antitumour agents against malignant melanoma. Cytotoxicity assays showed that N-4-hydroxyphenylglycine (NHPG) and its alpha-methyl derivatives methylphenylglycine and dimethylphenylglycine exhibit significant antiproliferative effects on pigmented human melanoma cell lines (HBL), with inhibitory concentrations at 50% (IC50) around 80 micrograms/ml. A marked increase in cytotoxicity was observed with morpholine-containing 4-aminophenols, e.g. N-(2-morpholinoethyl)-4-aminophenol, which showed an IC50 of 20 micrograms/ml of HBL cells. Much more pronounced was the effect of the diacetoxy-derivative, DiAcMoAc, which showed an IC50 of 15 micrograms/ml on HBL cells and as low as 2 micrograms/ml on tyrosinase-containing, non-pigmented human melanoma cells (LND1), with a toxicity response of the same order of magnitude as that of melphalan. These results open interesting perspectives in the design of new targeted pro-drugs against malignant melanoma.

Aminophenols↗
PubMed2003

The metabolic pathway of 4-aminophenol in Burkholderia sp. strain AK-5 differs from that of aniline and aniline with C-4 substituents.

Burkholderia sp. strain AK-5 utilized 4-aminophenol as the sole carbon, nitrogen, and energy source. A pathway for the metabolism of 4-aminophenol in strain AK-5 was proposed based on the identification of three key metabolites by gas chromatography-mass spectrometry analysis. Strain AK-5 converted 4-aminophenol to 1,2,4-trihydroxybenzene via 1,4-benzenediol. 1,2,4-Trihydroxybenzene 1,2-dioxygenase cleaved the benzene ring of 1,2,4-trihydroxybenzene to form maleylacetic acid. The enzyme showed a high dioxygenase activity only for 1,2,4-trihydroxybenzene, with K(m) and V(max) values of 9.6 micro M and 6.8 micro mol min(-1) mg of protein(-1), respectively.

Aminophenols↗
PubMed1996

2-aminophenol 1,6-dioxygenase: a novel aromatic ring cleavage enzyme purified from Pseudomonas pseudoalcaligenes JS45.

Most bacterial pathways for the degradation of aromatic compounds involve introduction of two hydroxyl groups either ortho or para to each other. Ring fission then occurs at the bond adjacent to one of the hydroxyl groups. In contrast, 2-aminophenol is cleaved to 2-aminomuconic acid semialdehyde in the nitrobenzene-degrading strain Pseudomonas pseudoalcaligenes JS45. To examine the relationship between this enzyme and other dioxygenases, 2-aminophenol 1,6-dioxygenase has been purified by ethanol precipitation, gel filtration, and ion exchange chromatography. The molecular mass determined by gel filtration was 140,000 Da. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed two subunits of 35,000 and 39,000 Da, which suggested an alpha2beta2 subunit structure. Studies with inhibitors indicated that ferrous iron was the sole cofactor. The Km values for 2-aminophenol and oxygen were 4.2 and 710 microM, respectively. The enzyme catalyzed the oxidation of catechol, 6-amino-m-cresol, 2-amino-m-cresol, and 2-amino-4-chlorophenol. 3-Hydroxyanthranilate, protocatechuate, gentisate, and 3- and 4-methylcatechol were not substrates. The substrate range and the subunit structure are unique among those of the known ring cleavage dioxygenases.

Aminophenols↗
PubMed1983

Decreasing inhibitory potency of prostaglandin synthetase inhibitors during their cooxidative metabolism. Studies on aminophenols, pyrazolon derivatives and 1,3-diphenylisobenzofuran.

A variety of prostaglandin synthetase inhibitors are cooxygenated during arachidonic acid peroxidation catalyzed by rat renal medulla prostaglandin synthetase or soybean lipoxygenase. Phenylbutazone, aminopyrine, 1,3-diphenylisobenzofuran, paracetamol, p-aminophenol, p-phenetidine and other o- and m-substituted aminophenol derivatives were cooxygenated, whereby prostaglandin synthetase inhibition was significantly weakened due to the formation of less inhibitory metabolites. In contrast, the inhibitory potency of diclofenac, indomethacin and phenacetin and its analogues remained unchanged during prostaglandin synthesis inhibition, because these compounds were no suitable cooxygenation substrates. Evidence is given that quinone imines may not be involved in the cooxidative metabolism of paracetamol and other aminophenols. As to the mechanisms of cooxygenation of suitable substrates dependent on their chemical structures either the arachidonic acid oxygenase or the subsequent hydroperoxidase reaction may trigger the oxygenation. 1,3-Diphenylisobenzofuran is metabolized during the formation of arachidonic acid hydroperoxides in contrast to paracetamol, which requires an additional peroxidase reaction to yield reactive metabolites.

Acetaminophen↗
PubMed1982

Genotoxic activity of the aminophenols as evidenced by the induction of sister chromatid exchanges.

1 Most hair dyes contain the structural isomers ortho-, meta- and para- aminophenol which were investigated concerning their ability to induce sister chromatid exchanges (SCE) in cultured human lymphocytes in vitro and in Chinese hamster bone marrow cells in vivo. 2 In vitro only ortho-aminophenol significantly induced SCE in a dose-dependent manner. 3 In vivo none of the structural isomers increased significantly the SCE frequency. 4 It is concluded that ortho-aminophenol is a weak directly acting compound which is detoxified during its metabolism.

Aminophenols↗
PubMed1991

Nephrotoxicity of 4-aminophenol glutathione conjugate.

4-Aminophenol (p-aminophenol, PAP) causes selective necrosis to the pars recta of the proximal tubule in Fischer 344 rats. The basis for this selective toxicity is not known, but PAP can undergo oxidation in a variety of systems to form the 4-aminophenoxy free radical. Oxidation or disproportionation of this radical will form 1,4-benzoquinoneimine which can covalently bind to tissue macromolecules. Recent studies have shown that certain benzoquinol-glutathione conjugates can cause renal necrosis in rats. We have synthesized a putative glutathione conjugate of PAP. The effect on the kidney of this conjugate and the sulphate and N-acetyl conjugates, known metabolites of PAP, have been examined in Fischer 344 rats. 4-Amino-3-S-glutathionylphenol produced a dose-dependent (92-920 mumol kg-1) necrosis of the proximal tubular epithelium and altered renal excretory function. The lesion at the low dose was restricted to the pars recta of the proximal tubule in the medullary rays, while at the higher doses it affected the pars recta region of all nephrons. In contrast, PAP-O-sulphate and N-acetyl-4-aminophenol (paracetamol) caused no histological or functional alteration to the kidney at 920 mumol kg-1. The renal necrosis produced by 4-amino-3-S-glutathionylphenol was very similar to that produced by PAP (367-920 mumol kg-1), both functionally and histologically, except that smaller doses of the glutathione conjugate were required. These studies indicate that glutathione conjugation of PAP generates a metabolite that is more toxic to the kidney than the parent compound. A possible mechanism of toxicity (analogous to that reported for glutathione conjugates of certain quinones) involving oxidation to form a 1,4-benzoquinoneimine thioether that could redox cycle is discussed.

Acetaminophen↗
PubMed1989

Effects of sulphydryl reagents on the formation of the aniline metabolite 4-aminophenol and its sulphate and glucuronide conjugates in primary cultures of rat hepatocytes.

1. The effects of various sulphydryl-blocking reagents on aniline biotransformation and cytochrome P-450 levels were studied in cultured rat hepatocytes. 2. Exposure of aniline-metabolizing hepatocytes to p-chloro-mercuribenzoate (PCMB) or p-chloromercuribenzenesulphonic acid (PCMBS) resulted in decreased levels of cytochrome P-450, decreased glucuronidation of 4-aminophenol and increased levels of free 4-aminophenol. 3. Incubation of aniline-metabolizing hepatocytes with disulfiram resulted in decreased formation of 4-aminophenol, but this was not associated with impaired glucuronidation or cytochrome P-450 levels. 4. Exposure of aniline-metabolizing hepatocytes to mersalyl, 2,2'-dithiodipyridine (DTP), 6,6'-carboxydipyridine disulphide (CPDS) or N-ethylmaleimide did not affect the biotransformation of aniline or cytochrome P-450 levels. 5. Metyrapone prevented degradation of cytochrome P-450. Exposure of cells to SKF-525 A inhibited aniline biotransformation without altering cytochrome P-450 levels. 6. PCMB and PCMBS inhibited aniline metabolism, probably by binding to a cysteinyl-SH residue in cytochrome P-450 apoenzyme and 'active sites' of UDP-glucuronyl transferases. Disulfiram inhibited aniline biotransformation, probably indirectly by diminishing NADPH.

Aminophenols↗
PubMed1990

Activation and detoxication of aminophenols. II. Synthesis and structural elucidation of various thiol addition products of 1,4-benzoquinoneimine and N-acetyl-1,4-benzoquinoneimine.

1. Nine thioethers of 4-aminophenol with beta-hydroxyethylmercaptan, ranging from mono- to tetra-substituted thioadducts, were prepared from synthetic 1,4-benzoquinoneimine and characterized by 1H-n.m.r. and u.v. spectroscopy. For each compound, extinction coefficients and pKa values of the amino group were determined. 2. Five thioethers of 4-aminophenol with glutathione (GSH) were prepared and characterized by 1H-n.m.r. and u.v. spectroscopy with their respective extinction coefficients and pKa values. Two further thioadducts were tentatively assigned by their u.v. spectroscopic properties. 3. Reaction products of 1,4-[U-14C]benzoquinoneimine and GSH were studied, indicating formation of 4-amino-2-(glutathione-S-yl)phenol, 4-amino-2,3,6-tris(glutathione-S-yl)phenol as the main products. Formation of glutathione disulphide (GSSG) was not detected. In contrast, N-acetyl-1,4-[U-14C]benzoquinoneimine was partly reduced by GSH and formed only the 2-substituted thioadduct. 4. Investigation of the product orientation in the reductive addition of GSH to 2-(glutathione-S-yl)-1,4-benzoquinoneimine and 3-(glutathione-S-yl)-1,4-benzoquinoneimine, respectively, showed that the 3-substituted derivative formed mainly the 3,5-di-substituted thioadduct, whereas the 2-substituted compound formed mainly the 2,3,6-tri-substituted thioadduct. 5. Formation of thioadducts which autoxidize markedly faster than the parent aminophenol indicates that thioether formation is not an obligatory detoxication process.

Aminophenols↗
PubMed2000

Isolation and characterization of a Pseudomonas sp. strain PH1 utilizing meta-aminophenol.

Pseudomonas sp. strain PH1 was isolated from soil contaminated with pharmaceutical and dye industry waste. The isolate PH1 could use m-aminophenol as a sole source of carbon, nitrogen, and energy to support the growth. PH1 could degrade up to 0.32 mM m-aminophenol in 120 h, when provided as nitrogen source at 0.4 mM concentration with citrate (0.5 mM) as a carbon source in the growth medium. The presence of ammonium chloride as an additional nitrogen source repressed the degradation of m-aminophenol by PH1. To identify strain PH1, the 16S rDNA sequence was amplified by PCR using conserved eubacterial primers. The FASTA program was used to analyze the 16S rDNA sequence and the resulting homology patterns suggested that PH1 is a Pseudomonas.

Aminophenols↗
PubMed1997

Quantitative colorimetric determination of urinary p-aminophenol with an automated analyzer.

We developed an automated colorimetric method for the quantitative determination of p-aminophenol with a Cobas Mira analyzer. The procedure can be used for the biological monitoring of human exposure to aniline. An absorbed aniline dose is extensively oxidized to p-aminophenol, which is excreted in urine mainly as glucurono- and sulfo- conjugates. After enzymatic hydrolysis, we reacted the free compound with resorcinol in the presence of manganese ions to form an indophenol dye, which is measured at 550 nm. Excellent accuracy (102.8%, 103.9%, and 96.8% at 2.5, 50, and 90 mg/L, respectively) and precision (7.7%, 2.1%, and 0.8% CV for within-run and 11.1%, 4.7%, and 4.6% for total reproducibility at 2.5, 50, and 90 mg/L, respectively) were achieved over a linear concentration range of 2.0 to 100 mg/L. The detection limit was 0.9 mg/L and no significant interference (except for o-aminophenol) was found for several investigated drugs and related compounds. The proposed method was used for a stability study and to analyze several samples from an occupational health screen.

Adult↗
PubMed1976

Spectrophotometric determination of p-aminophenol alone or in the presence of acetaminophen.

Small amounts of p-aminophenol were analyzed quantitatively by mixing with 4-nitro- or 2,4-dinitrobenzaldehyde in neutral alcoholic solution and then quantitatively forming the respective Schiff bases, 4'-nitro- and 2',4'-dinitrobenzylidene-4-hydroxyaniline, by evaporating the alcoholic solutions to dryness. The Schiff bases thus formed were examined spectrophotometrically. This procedure was also used for the determination of p-aminophenol in the presence of its degradation products. It was necessary, however, to separate the respective Schiff bases by TLC from the degradation products and the reaction mixture prior to spectrophotometric examination. Small amounts of p-aminophenol present in acetaminophen were quantitatively determined by applying the procedure to a water-ethanol (95:5 v/v) extract of the samples of acetaminophen. TLC was used to separate the respective Schiff bases from the reaction mixture and acetaminophen prior to spectrophotometric examination.

Acetaminophen↗
PubMed1997

Interaction of o-Aminophenol and o-Nitrophenol with Copper, Zinc, Molybdenum, and Chromium Ferrocyanides

Removal of o-aminophenol and o-nitrophenol from aqueous solution through adsorption on copper zinc, molybdenum, and chromium ferrocyanides were studied in pH range 2-10 at 27°C. At pH 7.0 o-nitrophenol adsorbed more than o-aminophenol on all the metal ferrocyanides studied. The Langmuir type of adsorption is followed in the concentration range of 10(-3) to 10(-4) M of o-aminophenol and o-nitrophenol solutions. Copyright 1997 Academic Press. Copyright 1997Academic Press

Journal Article↗
PubMed2006

Synthesis, structure, and characterization of molybdenum(VI) imido complexes with N-salicylidene-2-aminophenol.

Diimido complexes of the type Mo(NAr)2Cl2(dme) (dme = 1,2-dimethoxyethane) react with N-salicylidene-2-aminophenol (sapH2) in methanol in the presence of 2 equiv of triethylamine to form complexes with the general formula Mo(NAr)(1,2-OC6H4NH)(sap). The structures of three of these compounds (NAr = 2,6-dimethylphenylimido (1), 2,4,6-trimethylphenylimido (2), 2-tert-butylphenylimido3) have been determined by X-ray crystallography. The coordination sphere around the Mo is a distorted octahedron. The oxygen from the 2-aminophenol is trans to the imido nitrogen, whereas the amido nitrogen and the tridentate sap occupy the four equatorial positions. The Mo-N-C imido linkages have angles of 167.5(2) degrees (1), 163.2(2) degrees (2), and 162.4(1) degrees (3). A precursor complex to the imido-amido complex, Mo(NAr)(sap)(OCH3)2 (4, NAr = 2,4,6-trimethylphenylimido), has been isolated and characterized. Compound 4 reacts with 2-aminophenol to form 2, with 2-aminothiophenol to form Mo(NAr)(1,2-SC6H4NH)(sap) (5), with catechol to form Mo(NAr)(1,2-OC6H4O)(sap) (6), with naphthalene-2,3-diol to form Mo(NAr)(naphthalene-2,3-diolate)(sap) (7), with 1,2-benzenedithiol to form Mo(NAr)(1,2-SC6H4S)(sap) (8), and with 1,2-phenylenediamine to form Mo(NAr)(1,2-HNC6H4NH)(sap) (9). The structures of compounds 5-9 have been determined by X-ray crystallography. With the exception of compound 8, the structures are similar to those of 1,2, and 3, with the bidentate ligand occupying one axial and one equatorial position. In 8, 1,2-benzendithiolate occupies two equatorial positions, and the nitrogen from sap is located trans to the imido nitrogen. All complexes were characterized by 1H NMR spectroscopy, cyclic voltammetry, and UV-vis spectroscopy. When a solution of 4 is exposed to moisture-containing air, MoO2(sap)(CH3OH) (10) is formed. The structure of 10 was also determined.

Journal Article↗