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PubMed1998

Evaluation of Alcaligenes eutrophus cells as an NADH regenerating catalyst in organic-aqueous two-phase system.

A soluble NAD-dependent hydrogenase contained in Alcaligenes eutrophus was evaluated as a coenzyme regenerating catalyst in an organic-aqueous two-phase (predominantly organic) system. The horse-liver alcohol-dehydrogenase (HLADH) catalyzed reduction of cyclohexanone to cyclohexanol was used as a model reaction. The impact of different solvents (selected to span a large variety of principal properties) on the stability and activity of the HLADH, using substrate-driven regeneration, was studied. Solvents suitable for the HLADH were then selected for an evaluation of the hydrogenase-driven coenzyme regeneration. Hydrophobic solvents such as heptane, toluene, and 1,1,1-trichloroethane were found to be suitable for the coupled reactions catalyzed by HLADH and hydrogenase. Nonimmobilized cells, permeabilized with cetyl-trimethyl-ammonium bromide, were the most efficient preparation for the regeneration of NADH. The use of this preparation in heptane (10% water) was optimized with respect to the yield obtained in the HLADH-catalyzed reduction of cyclohexanone. Using the optimized conditions, yields of 99% cyclohexanol were obtained.

Alcaligenes↗

PubMed2007

Catalysis of a peptidic micellar assembly covalently immobilized within mesoporous silica channels: importance of amphiphilic spatial design.

A mesostructured silica/organic composite 1-MS, constructed from a rodlike micelle of amino acid amphiphile 1 that has a condensable head group and that can be used as a template, was found to be able to catalyze the acetalization of cyclohexanone, in ethanol at 25 degrees C (50% in 12 h), whereas no reaction took place with unfunctionalized mesoporous silica. In sharp contrast, hydrolytic removal of the C16 alkyl tail of immobilized 1 resulted in the complete disappearance of the catalytic activity, which suggests the importance of a hydrophobic inner domain for the admission of cyclohexanone. Unsupported peptide amphiphile 2, under identical conditions to those above, was inefficient for acetalization regardless of the absence (2% in 24 h) or presence of mesoporous silica (7% in 24 h). Reference composite 2-MS, which is a noncovalently immobilized peptidic micelle, was virtually inactive (1% in 24 h). These observations indicate the importance of covalent immobilization of the peptidic rod micelle for catalysis. Mesostructured silicate 3-MS hybridized with a nonpeptidic, ammonium ion amphiphile (3) showed a certain catalytic activity, but the yield (12% in 24 h) of the acetal was much lower than that achieved by using 1-MS as the catalyst. Amorphous silica with immobilized 1 on its surface was much less active than 1-MS for acetalization (5% in 24 h).

Acetals↗

PubMed1987

Assessment of the safety of chemicals administered intravenously in the neonatal rat.

A 3-day-old neonatal rat model for the safety assessment of various drugs, chemicals, and nutrients administered intravenously is described. This model was used to assess the safety of di(2-ethylhexyl) phthalate (DEHP), cyclohexanone, and a 3:1 mixture of medium and long-chain triglyceride emulsions following subchronic administration using the intravenous route. The administration of DEHP at dosage of 164.8 mg/kg for 18 consecutive days resulted in a small but statistically significant increase in liver weight and SGOT activity. However, no conclusive histopathological alternations could be discerned between livers from DEHP and normal saline (control) animals. No effects were observed among neonates treated with cyclohexanone at dosages up to 25 mg/kg for 18 consecutive days. Because of technical difficulties emanating from high dosage volumes, the administration of lipid emulsion mixture lasted 9 consecutive days only. Except for transient ataxia and sedation, no adverse effects were observed among neonates that received 3:1 medium- and long-chain triglyceride emulsion for 9 consecutive days beginning on day 3 postpartum. No adverse effects were observed among neonates receiving the lipid emulsions for 7 consecutive days beginning on day 12 postpartum.

Animals↗

PubMed1998

Oxidative effects in human erythrocytes caused by some oximes and hydroxylamine.

Both oximes and hydroxylamine (HYAM) are compounds with known oxidative capacity. We tested in vitro whether acetaldoxime (AAO), cyclohexanone oxime (CHO), methyl ethyl ketoxime (MEKO) or HYAM affect haemoglobin oxidation (into HbFe3+), formation of thiobarbituric acid reactive substances (TBARS), and glutathione (GT) depletion in human haemolysate, erythrocytes or blood. All these parameters are known to be related to oxidative stress. Glutathione S-transferase (GST) activity was measured as it may be affected by oxygen radicals. All three oximes caused a low degree of HbFe3+ accumulation in erythrocytes. This was higher in haemolysates indicating that membrane transport may be limiting or that protective mechanisms within erythrocytes are more effective. HbFe3+ accumulation was lower for the oximes than for HYAM. AAO and HYAM caused TBARS formation in blood. For HYAM this was expected as free radicals are known to be generated during HbFe3+ formation. Free radical generation by AAO and HYAM in erythrocytes was confirmed by the inhibition of GST. For the other two oximes (CHO and MEKO) some special effects were found. CHO did inhibit erythrocyte GST while it did not cause TBARS formation. MEKO was the least potent oxime as it caused no TBARS formation, little HbFe3+ accumulation and little GST inhibition in erythrocytes. However, GT depletion was more pronounced for MEKO than for the other oximes, indicating that glutathione conjugation occurs. TBARS formation, GT depletion and GST modulation caused by the oximes and HYAM were also tested in rat hepatocytes. However, no effects were found in hepatocytes. This suggests that a factor present in erythrocytes is necessary for free radical formation. Studies with proposed metabolites of the oximes (i.e. cyclohexanone, acetaldehyde or methylethyl ketone) and addition of rat liver preparations to the erythrocyte incubations with oximes, suggest that metabolism is not a limiting factor in erythrocyte toxicity.

Animals↗

PubMed1988

Spine density on olfactory granule cell dendrites is reduced in rats reared in a restricted olfactory environment.

The Golgi technique was used to study the development of spines on the external dendrites of granule cells in the olfactory bulbs of young rats that had been continuously exposed to cyclohexanone vapor, deodorized air, or rat odors. Exposure to deodorized air for 3 weeks from postnatal day 1 reduced spine density on the medial and lateral sides of the bulb, whilst exposure to cyclohexanone reduced spine density on the lateral side only. These reductions were evident in other animals exposed for 7 weeks. With all treatments, spine density reached a maximum at postnatal day 21 and decreased markedly during the next month.

Age Factors↗

PubMed2006

Storage stability of ketones on carbon adsorbents.

Activated coconut carbon constitutes the more widely used sorbent for preconcentration of volatile organic compounds in sampling workplace air. Water vapour is always present in the air and its adsorption on the activated carbon surface is a serious drawback, mainly when sampling polar organic compounds, such as ketones. In this case, the recovery of the compounds diminishes; moreover, ketones can be decomposed during storage. Synthetic carbons contain less inorganic impurities and have a lower capacity for water adsorption than coconut charcoal. The aim of this work was to evaluate the storage stability of various ketones (acetone, 2-butanone, 4-methyl-2-pentanone and cyclohexanone) on different activated carbons and to study the effect of adsorbed water vapour under different storage conditions. The effect of storage temperature on extraction efficiencies was significant for each ketone in all the studied sorbents. Recovery was higher when samples were stored at 4 degrees C. The results obtained for storage stability of the studied ketones showed that the performance of synthetic carbons was better than for the coconut charcoals. The water adsorption and the ash content of the carbons can be a measure of the reactive sites that may chemisorb ketones or catalize their decomposition. Anasorb 747 showed good ketone stability at least for 7 days, except for cyclohexanone. After 30-days storage, the stability of the studied ketones was excellent on Carboxen 564. This sorbent had a nearly negligible ash content and the adsorbed water was much lower than for the other sorbents tested.

Acetone↗

PubMedDate not supplied

Understanding and improving NADPH-dependent reactions by nongrowing Escherichia coli cells.

We have shown that whole Escherichia coli cells overexpressing NADPH-dependent cyclohexanone monooxygenase carry out a model Baeyer-Villiger oxidation with high volumetric productivity (0.79 g epsilon-caprolactone/L.h ) under nongrowing conditions (Walton, A. Z.; Stewart, J. D. Biotechnol. Prog. 2002, 18, 262-268). This is approximately 20-fold higher than the space-time yield for reactions that used growing cells of the same strain. Here, we show that the intracellular stability of cyclohexanone monooxygenase and the rate of substrate transport across the cell membrane were the key limitations on the overall reaction duration and rate, respectively. Directly measuring the levels of intracellular nicotinamide cofactors under bioprocess conditions suggested that E. coli cells could support even more efficient NADPH-dependent bioconversions if a more suitable enzyme-substrate pair were identified. This was demonstrated by reducing ethyl acetoacetate with whole cells of an E. coli strain that overexpressed an NADPH-dependent, short-chain dehydrogenase from baker's yeast (Saccharomyces cerevisiae). Under glucose-fed, nongrowing conditions, this reduction proceeded with a space-time yield of 2.0 g/L.h and a final product titer of 15.8 g/L using a biocatalyst:substrate ratio (g/g) of only 0.37. These values are significantly higher than those obtained previously. Moreover, the stoichiometry linking ketone reduction and glucose consumption (2.3 +/- 0.1) suggested that the citric acid cycle supplied the bulk of the intracellular NADPH under our process conditions. This information can be used to improve the efficiency of glucose utilization even further by metabolic engineering strategies that increase carbon flux through the pentose phosphate pathway.

Acinetobacter↗

PubMed2004

Novel fragmentation reaction of 2-alkyl- and 2,4-dialkyl-3-iodo-1-oxocyclohexan-2,4-carbolactones.

2-Alkyl- and 2,4-dialkyl-3-iodo-1-oxocyclohexan-2,4-carbolactones undergo lithium hydroxide- and lithium alkoxide-induced fragmentation reactions to provide butenolides, gamma-hydroxycyclohexenones, and/or gamma-butyrolactones. In general, product distribution is governed by two factors: (1) the nature of nucleophiles and (2) the steric bulkiness of the substituents at C-2 and C-4 of the cyclohexanones. Lithium hydroxide-induced fragmentation provides butenolides and gamma-hydroxycyclohexenones. In contrast, lithium alkoxide-promoted fragmentation results in predominantly 5-substituted gamma-butyrolactones along with a small amount of butenolides in limited cases. Fragmentation products induced by lithium hydroxide are largely influenced by the steric bulkiness of the substituents at C-2 and C-4 of the cyclohexanone ring. The bulky substituents render the exclusive formation of butenolides.

Catalysis↗

PubMed1999

Odorants presented to the rat nasal cavity increase cortical blood flow.

Complaints about unpleasant environmental odorants, both outdoor and indoor, are increasingly being reported. The main complaints of health symptoms from environmental odorants are eye, nose and throat irritation, headache and drowsiness. Complaints may arise from the stimulation of olfactory receptors or trigeminal chemoreceptors. Stimulation of cerebrovascular nociceptors originating from a branch of the trigeminal nerve may be associated with an increase in cortical blood flow which is thought to be related to headache. Since odorants are reported to elicit headaches, the possibility that odorants may increase cortical blood flow was examined. Cortical blood flow was monitored in rats using a laser-Doppler flowmeter. The flowmeter probe was placed over the left frontal cortex while propionic acid, cyclohexanone, amyl acetate or butanol was delivered to the nasal cavity via an olfactometer. Cortical blood flow increased as the concentration increased for three of the odorants tested. The greatest increase in blood flow occurred to the presentation of propionic acid, followed by cyclohexanone and amyl acetate. There was no response to butanol. These data demonstrate that odorants can alter cerebrovascular blood flow, which may account, in part, for one of the health symptoms reported for odorants.

Animals↗

PubMed1989

Analysis of the inactivation of liver alcohol dehydrogenase during storage in Aerosol-OT/isooctane microemulsions.

Changes in the enzymatic properties of horse liver alcohol dehydrogenase (HLADH; EC 1.1.1.1) were studied as a function of incubation time in Aerosol-OT/isooctane microemulsions. The enzyme was characterized by fluorimetric binding studies of the inhibitor isobutyramide to the binary complex, HLADH-NADH and by determination of Km,app and Vmax,app values for cyclohexanone. The Km,app values for cyclohexanone and the Kd,app for isobutyramide stay constant throughout a 48-h incubation, whereas the Vmax,app and the total number of inhibitor binding sites decrease. Thus the inactivation process previously described corresponds to progressive loss of functional sites, while the properties of the remaining functional sites are unchanged. If no co-enzyme is added to the system, the enzyme loses catalytic activity within less than an hour, but if co-enzyme is added, a fraction of the HLADH enzyme population retains enzyme activity over a long period of time. Hence the presence of bound co-enzyme significantly inhibits the process(es) leading to inactivation of the enzyme in the microemulsions.

Aerosols↗

PubMed1982

Metabolism of cyclohexaneacetic acid and cyclohexanebutyric acid by Arthrobacter sp. strain CA1.

A strain of Arthrobacter was isolated by enrichment culture with cyclohexaneacetate as the sole source of carbon and grew with a doubling time of 4.2 h. In addition to growing with cyclohexaneacetate, the organism also grew with cyclohexanebutyrate at concentrations not above 0.05%, and with a variety of alicyclic ketones and alcohols. Oxidation of cyclohexaneacetate proceeded through formation of the coenzyme A (CoA) ester followed by initiation of a beta-oxidation cycle. beta-Oxidation was blocked before the second dehydrogenation step due to the formation of a tertiary alcohol, and the side chain was eliminated as acetyl-CoA by the action of (1-hydroxycyclohexan-1-yl)acetyl-CoA lyase. The cyclohexanone thus formed was degraded by a well-described route that involves ring-oxygen insertion by a biological Baeyer-Villiger oxygenase. All enzymes of the proposed metabolic sequence were demonstrated in cell-free extracts. Arthrobacter sp. strain CA1 synthesized constitutive beta-oxidative enzymes, but further induction of enzymes active toward cyclohexaneacetate and its metabolites could occur during growth with the alicyclic acid. Other enzymes of the sequence, (1-hydroxycyclohexan-1-yl)acetyl-CoA lyase and enzymes of cyclohexanone oxidation, were present at negligible levels in succinate-grown cells but induced by growth with cyclohexaneacetate. The oxidation of cyclohexanebutyrate was integrated into the pathway for cyclohexaneacetate oxidation by a single beta-oxidation cycle. Oxidation of the compound could be divided into two phases. Initial oxidation to (1-hydroxycyclohexan-1-yl)acetate could be catalyzed by constitutive enzymes, whereas the further degradation of (1-hydroxycyclohexan-1-yl)acetate was dependent on induced enzyme synthesis which could be inhibited by chloramphenicol with the consequent accumulation of cyclohexaneacetate and (1-hydroxycyclohexan-1-yl)acetate.

Acetates↗

PubMed2003

The first example of alpha-thiomagnesiums generated from dithioacetal monoxides with Grignard reagent; their properties and some synthetic applications.

Dithioacetal monoxides were synthesized from aldehydes and cyclohexanone, and reaction of the dithioacetal monoxides with Grignard reagents was investigated. The dithioacetal monoxide synthesized from alkylaldehyde and 4-chlorobenzenethiol reacted with i-PrMgCl to afford the desired alpha-thiomagnesium in high yield. The generated alpha-thiomagnesium was found to be stable at room temperature and to be useful in organic synthesis. In contrast to this, the dithioacetal monoxides derived from benzaldehyde and cyclohexanone did not give satisfactory results.

Acetals↗

PubMed1989

Metabolism of a monoterpene ketone, R-(+)-pulegone--a hepatotoxin in rat.

1. R-(+)-Pulegone was administered orally to rats and the urinary metabolites were investigated. Six metabolites were isolated and purified using column and thin layer chromatographic techniques. Metabolites were identified by i.r., n.m.r. and mass spectral analyses. 2. The neutral metabolites isolated from urine of rats treated with pulegone (I) were: pulegone (II), 2-hydroxy-2(1'-hydroxy-1'-methylethyl)-5-methylcyclohexanone (III), 3,6-dimethyl-7a-hydroxy-5,6,7,7a-tetrahydro-2(4H)-benzofuranone (V) and menthofuran (VII). Metabolites II and III were also excreted in conjugated form. 3. Acidic metabolites isolated from urine of rats treated with pulegone (I) were: 5-methyl-2(1'-methyl-1'-carboxyethylidene)cyclohexanone (IV) and 5-methyl-5-hydroxy-2(1'hydroxy-1'-carboxyethyl)cyclohexanone (VI).

Administration, Oral↗

PubMed1999

[Gas chromatography-infrared spectroscopy(GC-IR) analysis of the oxidation products of cyclohexene].

Gas chromatography-infrared spectroscopy technique integrates the excellent resolution ability of GC with the structural information of IR. Based on the GC and IR spectra, the complicated products of a reaction can be analyzed quantitatively and qualitatively. From the analysis of the products, the reaction process and its mechanism can be elucidated. In this work, analysis by GC-IR of the oxidation products of cyclohexene catalyzed by zeolite TS-1 in H2O2 was performed. The products are 2-cyclohexenone, 2-cyclohexen-1-ol and 2,3-epoxy-1-cyclohexanone. 2,3-Epoxy-1-cyclohexanone is an unexpected product. It must be a further oxidation product of 2-cyclohexenone. From the analysis, the reaction mechanisms were presumed.

Alkanes↗

PubMedDate not supplied

Evaluation of the role of free hydroxyl radicals in the cytochrome P-450-catalyzed oxidation of benzene and cyclohexanol.

The possible role of free hydroxyl radicals in the oxidation of cyclohexanol to cyclohexanone and of benzene to phenol was examined in a reconstituted system containing rabbit phenobarbital-inducible P-450LM2. From steady state kinetic studies, a KM for cyclohexanol of 8.7 mM and a Vmax of 5.7 nmol of cyclohexanone formed/min/nmol of P-450 were determined. Similarly, a KM for benzene of 105 mM and a Vmax of 22 nmol of phenol formed/min/nmol of P-450 were obtained. With intact microsomes from phenobarbital-treated rabbits, a KM for benzene of 18 mM and a Vmax of 1.7 nmol of phenol formed/min/nmol of P-450 were determined. With the use of substrate concentrations in the range of the respective KM values, superoxide dismutase, desferrioxamine, and dimethyl sulfoxide were found to have no significant effect on the P-450-catalyzed reactions. When the oxidation of benzene or cyclohexanol was examined in a model hydroxyl radical-generating system containing xanthine, xanthine oxidase, and Fe-EDTA, no dependence of the rate of oxidation on the substrate concentrations used was observed. Since the rate of hydroxyl radical generation by the model system was adjusted to be greater than the rate of product formation in the P-450 system, the lack of dependence on substrate concentration suggests that free hydroxyl radicals are not involved in the P-450-catalyzed reactions studied. Taken together, these findings indicate that the free hydroxyl radical-mediated pathway observed by other investigators does not contribute significantly to product formation when these substrates are present at concentrations within the range of their respective KM values.

Animals↗

PubMed2001

The 12,13-diol cyclization approach for a truly stereocontrolled total synthesis of epothilone B and the synthesis of a conformationally restrained analogue.

A highly convergent and stereocontrolled synthesis of epothilone B (1) has been developed. The epoxide moiety in 1 was generated by regioselective mesylation and base treatment of the 12,13-diol 30 which was formed by a chelate Cram controlled Grignard addition of 14 and methyl ketone 13. Both fragments were synthesized from the chiral carbon pool precursors (S)-citronellol and (S)-lactic acid, respectively. A highly diastereoselective aldol addition of epoxy-aldehyde 7 and the known Southern hemisphere ketone 8 delivered the full carbon skeleton, containing all the stereogenic centers of 1. Functional group manipulation, macrolactonization and removal of two protecting groups then yielded 1. The spatial closeness of the C4-beta-methyl and C6-methyl group in the crystal structure of 1 inspired us to connect them through a methylene bridge to give a cyclohexanone derivative. Thus, the Northern hemisphere aldehyde 7 was added to the enolate of the cyclohexanone 47. Further manipulations and macrolactonization delivered the conformationally restrained epothilone derivative 42.

Antineoplastic Agents↗

PubMed2006

Comparison of activity of immobilised and soluble metalloporphyrins by NO release of oximes by chemiluminescence.

The ongoing interest in very efficient systems for the imitation of cytochrome P-450-dependent monooxygenase reactions, consisting of metalloporphyrin and oxygen donor, prompted us to develop a method to compare the catalytic activity of soluble metalloporphyrins with those which have been immobilised on different silica surfaces. In this article, we describe a method which allows direct comparison between the catalytic activities of soluble and immobilised metalloporphyrins by measuring the NO release of cyclohexanone oxime. We observed that all metalloporphyrins are able to enhance the NO release of cyclohexanone oxime in the presence of iodosobenzene as oxygen donor. In case of cationic metalloporphyrins, no difference in the catalytic activity was determined. In contrast, for perfluorinated metalloporphyrins we ascertained a major loss of activity after immobilisation. These results led us to the assumption that it is not easy to compare quantitative results of NO releases if soluble and immobilised metalloporphyrins were used.

Buffers↗

PubMed2007

The formation of byproducts in the autoxidation of cyclohexane.

In this work, a complementary experimental and theoretical approach is used to unravel the formation of byproducts in the autoxidation of cyclohexane. The widely accepted vision that cyclohexanone would be the most important precursor of undesired products was found inconsistent with several experimental observations. However, the propagation reaction of cyclohexyl hydroperoxide, which we recently put forward as the missing source of cyclohexanol and cyclohexanone, is now unambiguously identified also as the dominant path leading to byproducts. Indeed, this overlooked reaction produces large amounts of cyclohexoxy radicals, able to ring-open via a beta-C--C cleavage to omega-formyl radicals. The pathway by which these radicals are converted into the observed and quantified byproducts is derived in this work. In this liquid-phase reaction, solvent cages were found very important, steering the fate of nascent species.

Adipates↗