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At least 451 records · Page 25Linked to original sources
PubMed2001

Stereochemical aspects in the 4-vinylcyclohexene biotransformation with rat liver microsomes and purified p450s. monoepoxides and diols.

The stereochemical course of the biotransformation of 4-vinylcyclohexene (VCH, 1) by liver microsomes from male and female control and induced rats and purified rat P450 2B1 and 2E1 has been determined. The epoxidation of 1, catalyzed by male microsomes, occurs on both the endo- and exocyclic double bond to give four isomeric epoxides, cis-4-vinylcyclohexene 1,2-epoxide (2), trans-4-vinylcyclohexene 1,2-epoxide (3), (4R*,7S*)-4-vinylcyclohexene 7,8-epoxide (4), and (4R*,7R*)-4-vinylcyclohexene 7,8-epoxide (5). On the other hand, microsomes from female rats catalyzed primarily the endocyclic epoxidation. The stereoselectivity of this process was strongly dependent on gender and P450 induction. Only the phenobarbital and pyrazole, at lower levels, were able to enhance the epoxidation of 1 and mostly on the endocyclic double bond. Also, P450 2E1 and 2B1 in a reconstituted system were able to perform the epoxidation of 1 primarily on its endocyclic double bond. The metabolites, cis- and trans-4-vinylcyclohexene 1,2-epoxide (2 and 3, respectively) and the isomeric 4-vinylcyclohexene 7,8-epoxides (4 and 5), were rapidly biotransformed into the corresponding vicinal diols by mEH-catalyzed hydrolysis. The reaction of the endocyclic epoxides occurred with good substrate diastereo- and enantioselectivity favoring the hydrolysis of epoxides (1S,2R,4S)-3 and (1R,2S,4S)-2 to give, before 50% conversion, selectively (1R,2R,4S)-diol (6). At variance, the hydrolysis of the exocyclic epoxides was characterized by a high level of substrate enantioselection associated with a very low, if any, level of substrate diastereoselection, the two epoxides, (4R,7S)-4 and (4R,7R)-5, being hydrolyzed practically with the same rate. On the basis of the major resistance to mEH hydrolysis, the endocyclic epoxides, (1R,2S,4R)-3 and (1S,2R,4R)-2, are expected to be further oxidized, in a stereochemical manner, to the specific mutagenic diepoxides which are thought to play a crucial role in VCH ovotoxicity. Thus, VCH ovotoxicity may be markedly affected by the reactivity of the diepoxidic stereoisomers formed and detoxicated.

Animals↗
PubMed1999

Compound A uptake and metabolism to mercapturic acids and 3,3,3-trifluoro-2-fluoromethoxypropanoic acid during low-flow sevoflurane anesthesia: biomarkers for exposure, risk assessment, and interspecies comparison.

BACKGROUND: Sevoflurane is degraded during low-flow anesthesia to fluoromethyl-2,2-difluoro-1-(trifluoromethyl)vinyl ether ("compound A"), which causes renal necrosis in rats but is not known to cause nephrotoxicity in surgical patients. Compound A is metabolized to glutathione S-conjugates and then to cysteine S-conjugates, which are N-acetylated to mercapturic acids (detoxication pathway), or metabolized by renal beta-lyase to reactive intermediates (toxification pathway) and excreted as 3,3,3-trifluoro-2-fluoromethoxypropanoic acid. This investigation quantified compound A metabolites in urine after low-flow sevoflurane administration, to assess relative flux via these two pathways. METHODS: Patients (n = 21) with normal renal function underwent low-flow (11 min) sevoflurane anesthesia designed to maximize compound A formation. Inspiratory, expiratory, and alveolar compound A concentrations were quantified. Urine mercapturic acids and 3,3,3-trifluoro-2-fluoromethoxypropanoic acid concentrations were measured by gas chromatography and mass spectrometry. RESULTS: Sevoflurane exposure was 3.7 +/- 2.0 MAC-h. Inspired compound A maximum was 29 +/- 14 ppm; area under the inspired concentration versus time curve (AUCinsp) was 78 +/- 58 ppm x h. Compound A dose, calculated from pulmonary uptake, was 0.39 +/- 0.35 mmol (4.8 +/- 4.0 micromol/kg) and correlated with AUCinsp (r2 = 0.84, P < 0.001). Mercapturic acids excretion was complete after 2 days, whereas 3,3,3-trifluoro-2-fluoromethoxypropanoic acid excretion continued for 3 days in some patients. Total (3-day) mercapturates and fluoromethoxypropanoic acid excretion was 95 +/- 49 and 294 +/- 416 micromol, respectively (1.2 +/- 0.6 and 3.6 +/- 5.0 micromol/kg). CONCLUSION: Compound A doses during 3.7 MAC-h, low-flow sevoflurane administration in humans are substantially less than the threshold for renal toxicity in rats (200 micromol/kg). Compound A metabolites quantification may provide a biomarker for compound A exposure and relative metabolism via toxification and detoxication pathways. Compared with previous investigations, relative metabolic flux (fluoromethoxypropanoic acid/mercapturates) through the toxification pathway was sixfold greater in rats than in humans. Species differences in dose and metabolism may influence compound A renal effects.

Acetylation↗
PubMed1999

Identification of potent odorants in Japanese green tea (Sen-cha).

Application of aroma extract dilution analysis using the volatile fraction of a Japanese green tea (Sen-cha) sample resulted in the detection of 36 odor-active peaks with flavor dilution (FD) factors between 10 and 5000. Thirty-six potent odorants were identified from 36 odor-active peaks by gas chromatography/mass spectrometry (GC/MS) and/or the multidimensional GC/MS (MDGC/MS) system. Among these components, 4-methoxy-2-methyl-2-butanethiol (meaty), (Z)-1, 5-octadien-3-one (metallic), 4-mercapto-4-methyl-2-pentanone (meaty), (E,E)-2,4-decadienal (fatty), beta-damascone (honey-like), beta-damascenone (honey-like), (Z)-methyl jasmonate (floral), and indole (animal-like) showed the highest FD factors. Therefore, these odorants were the most important components of the Japanese green tea odor. In addition, 4-methoxy-2-methyl-2-butanethiol, 4-mercapto-4-methyl-2-pentanone, methional, 2-ethyl-3, 5-dimethylpyrazine, (Z)-4-decenal, beta-damascone, maltol, 5-octanolide, 2-methoxy-4-vinylphenol, and 2-aminoacetophenone were newly identified compounds in the green tea.

Gas Chromatography-Mass Spectrometry↗
PubMed2003

Squaric acid N-hydroxylamides: synthesis, structure, and properties of vinylogous hydroxamic acid analogues.

The synthesis of squaric acid N-hydroxylamide esters 5 and amides 6 from dimethyl squarate 2a is described. These derivatives are analogues of the naturally occurring iron(III) chelator hydroxamic acid. On the basis of a comparative reactivity study, a concerted retro-Cope mechanism for the formation of the N-hydroxylamide esters 5 by reaction of dimethyl squarate with hydroxylamines is proposed. A preliminary iron(III) binding study of these hydroxamic acid analogues is presented, demonstrating binding of iron(III) to amides 6 in aqueous solutions, while the esters 5 did not show any sign of metal ion binding. 13C NMR spectroscopic data (chemical shift and spin-lattice relaxation time determination) of these and related derivatives delineate the resonance structures predominant in these molecules. The resonance structures of the derivatives rationalize their spectroscopic data, chemical reactivity, and iron(III) binding properties. Single-crystal X-ray structure analyses of squaric acid N-hydroxylamide ester 5b and squaric acid N-hydroxylamide amide 6c confirm their connectivity and provide structural evidence supporting the spectroscopically derived conclusions. The squaric acid N-hydroxylamides are potentially useful in the construction of chemosensors for iron(III).

Binding, Competitive↗
PubMed1976

Mechanism of action of retinyl compounds on wound healing IV: effect of desmethylretinoic acid and its vinylogs on granuloma formation.

The effect of side-chain length of desmethylretinoic acid on granuloma formation induced by implantation of cotton pellets was studied. As in the homologous series of retinoic acid studies, compounds with side chains shorter than retinoic acid were not active while compounds with side chains as long or longer than retinoic acid were active. The compound with a chain two carbons longer than retinoic acid was the most active. The hydroxyproline and hexosamine contents of the granuloma were analyzed. The mechanisms of action of these active compounds on wound healing are discussed.

Animals↗
PubMed2000

Suppression of inducible nitric oxide synthase expression in RAW 264. 7 macrophages by two beta-carboline alkaloids extracted from Melia azedarach.

We investigated the mechanism of suppression of inducible nitric oxide synthase (iNOS) by two beta-carboline alkaloids isolated from Melia azedarach, 4,8-dimethoxy-1-vinyl-beta-carboline (compound 1, C-1) and 4-methoxy-1-vinyl-beta-carboline (compound 2, C-2). iNOS activity in a cell-free extract of lipopolysaccharide/interferon-gamma-stimulated RAW 264.7 cells was found to be markedly increased, and this increase was prevented by C-1 and C-2, accompanied by the parallel reduction in nitrite accumulation in culture medium. However, C-1 and C-2 had no further effect on the iNOS activity prepared from fully lipopolysaccharide/interferon-gamma-stimulated RAW 264.7 cells. Treatment with C-1 or C-2 decreased the levels of iNOS protein and mRNA in a concentration-dependent manner. In addition, prostaglandin E(2) production, cyclooxygenase-2 protein and DNA binding of nuclear factor-kappaB (NF-kappaB) in lipopolysaccharide-stimulated RAW 264.7 cells were reduced by these compounds. These results indicate that C-1 and C-2 primarily inhibit iNOS and cyclooxygenase-2 activities via the suppression of de novo synthesis of these two enzymes, and that the inhibition of iNOS expression may be associated with the inhibition of NF-kappaB activation. Taken together, the results suggest that suppression of iNOS and cyclooxygenase-2 induction by lipopolysaccharide is responsible for the anti-inflammatory activity of these alkaloids through selective inhibition of the expression of genes, which play important roles in inflammatory signaling pathways.

Alkaloids↗
PubMed2001

Determination and mass spectrometric investigation of a new mixed halogenated persistent component in fish and seal.

An unknown component that caused an intense signal in sample extracts of fish tissue was enriched and investigated using a variety of mass spectrometric techniques coupled to gas chromatographic separation. With the help of electron capture negative ion mass spectrometry (ECNI-MS) and electron impact mass spectrometry (EI-MS) it was established that the component carries 2Br and 3Cl atoms and forms a molecular ion at m/z 396. A concentrated solution of this mixed halogenated compound (MHC-1) was investigated by gas chromatography interfaced to electron impact high-resolution mass spectrometry (GC/EI-HRMS). Using full scan and SIM techniques, the molecular formula of MHC-1 was established to be C10H13Br2Cl3. This points toward MHC-1 having a monoterpene backbone. No chemical with this molecular formula has been synthesized, but two components with this composition have been earlier isolated from marine algae.

Alkenes↗
PubMed2005

Determination of polycyclic aromatic hydrocarbons in coffee brew using solid-phase extraction.

The presence of polycyclic aromatic hydrocarbons (PAHs) in coffee has been reported and is suspected to be due to the degradation of coffee compounds during the roasting step. Due to the high toxicity of these compounds, among which benzo[a]pyrene is known to be the most carcinogenic, their presence in the coffee, especially the coffee brew that is directly ingested by the consumer, is of prime importance. However, due to the low solubility of these compounds, their concentrations are expected to be rather low. As a consequence, reliable and sensitive analytical methods are required. The aim of this study was to develop a reliable and fast analytical procedure to determine these organic micropollutants in coffee brew samples. PAHs were retained on a 0.5 g polystyrene-divinylbenzene cartridge before being eluted by a mixture of methanol/tetrahydrofuran (10:90 v/v), concentrated, and directly analyzed by reversed-phase high-performance liquid chromatography coupled to a fluorescence detector. Application to the determination of PAHs in several coffee brew samples is also given, with mean estimated concentrations in the range of 0-100 ng L(-1) for suspected benzo[b]fluoranthene and benzo[a]pyrene, whereas no fluoranthene could be detected. Tentative identification was made on the basis of UV spectra. However, identification of the suspected traces of PAHs could not be achieved due to matrix effects, so that the presence of coeluting compounds may not be excluded.

Chromatography, High Pressure Liquid↗
PubMed2002

Effective and highly stereoselective coupling with vinyldiazomethanes to form symmetrical trienes.

Diazo coupling reactions are capable of forming E,E,E-trienes from cinnamaldehydes in good yield. An efficient methodology is reported for the production of styryldiazomethanes that are subsequently used with catalysis for coupling and for cyclopropanation. A vast difference in product selectivity is seen with styryldiazomethane generated from the corresponding hydrazone via manganese dioxide oxidation and that formed in situ by treatment of the tosylhydrazone sodium salt of cinnamaldehyde with transition metal catalysts. This observation impacts understanding of the reaction mechanism for diazo decomposition.

Alkenes↗
PubMed2001

Exploring a benzyloxyaniline linker utilizing ceric ammonium nitrate (CAN) as a cleavage reagent: solid-phase synthesis of N-unsubstituted beta-lactams and secondary amides.

[figure: see text] A novel benzyloxyaniline linker that uses ceric ammonium nitrate (CAN) as a cleavage reagent is described. Its application in the solid-phase synthesis of N-unsubstituted beta-lactams and secondary amides furnishes compounds in moderate to excellent yield (45-91%) and high purity (93-99%).

Amides↗
PubMed1999

Induction of cytochrome P-450 enzymes after repeated exposure to 4-vinylcyclohexene in B6C3F1 mice.

4-Vinylcyclohexene (VCH), an ovarian toxicant in mice, is known to irreversibly deplete ovarian follicles as a consequence of VCH diepoxide formation. Because ovotoxicity requires repeated dosing of VCH, the effect of consecutive daily doses of VCH (7.5 mmol/kg/day) on mouse liver microsomal activities and VCH epoxidation was determined. Cytochromes P-450 2B and 2A (CYP2B and CYP2A), principle isoforms involved in the bioactivation of VCH, as well as CYP2E1 and CYP3A were evaluated. VCH exposure increased total cytochrome P-450 content (35-83% above control levels) after either 5, 10, or 15 days of treatment. Western blot analysis revealed an induction of CYP2A, CYP2B, and CYP2E1 at day 10. Elevated levels of CYP2A and CYP2B correlated with marker androstenedione and testosterone 16alpha- and 16beta-hydroxylase activities. Microsomes prepared from mice pretreated with VCH for 10 days demonstrated an increase (>/=2-fold) in the rate of VCH monoepoxide and diepoxide formation. Microsomal VCH epoxidation was increased to a similar extent by phenobarbital, acetone, and dexamethasone treatment. An increase in cytosolic glutathione S-transferase activity was observed after repeated VCH treatment, an enzyme potentially involved in detoxification of the VCH epoxides. Interestingly, preliminary studies indicated that circulating levels of the monoepoxide (vinylcyclohexene 1, 2-monoepoxide) and diepoxide of VCH were elevated after repeated dosing of VCH. Overall, the results indicate that repeated exposure of VCH in mice induces cytochrome P-450-dependent activities, and in turn induction of its metabolism. Additional studies examining the toxicokinetics of VCH after repeated exposure are required to further delineate the relevance of induction in VCH-induced ovotoxicity.

Animals↗