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Epoxide
Kinds of Epoxide Terms modified by Epoxide Selected AbstractsCell Cycle Arrest and Apoptosis Induction by an Anticancer Chalcone EpoxideARCHIV DER PHARMAZIE, Issue 8 2010Haiyong Han Abstract Safe and effective chemotherapeutic agents for the treatment of pancreatic cancer remain elusive. We found that chalcone epoxides (1,3-diaryl-2,3-epoxypropanones) inhibited growth in two pancreatic cancer cell lines, BxPC-3 and MIA PaCa-2. Three compounds were active, with GI50 values of 5.6 to 15.8,µM. Compound 4a, 1,3-bis-(3,4,5-trimethoxyphenyl)-2,3-epoxypropanone, had an average GI50 of 14.1,µM in the NCI 60-cell-line panel. To investigate the mode of action, cell cycle analyses of BxPC-3 cells were carried out. Treatment of cells with 50,µM 4a resulted in dramatic accumulation at G2/M (61% after 12,h for 4avs. 15% for untreated cells). The cells rapidly entered apoptosis. After 12,h, 26% of cells treated with 50,µM 4a had entered apoptosis vs. 4% for cells treated with 100,µM etoposide and 2% for untreated cells. Compound 4a interfered with paclitaxel enhancement of tubulin polymerization, suggesting microtubules as the site of action. Reaction of thiol nucleophiles with 4a under basic conditions resulted in epoxide ring-opening and retroaldol fragmentation, yielding alkylated thiol. MALDI mass spectrometry showed that retroaldol reaction occurred upon treatment of ,-tubulin with 4a. The site of alkylation was identified as Cys354. Chalcone epoxides warrant further study as potential agents for treatment of cancer. [source] ChemInform Abstract: Expedient Asymmetric Synthesis of (2S,3S)-Boc-phenylalanine Epoxide (X), a Key Intermediate for the Synthesis of Biologically Active Compounds.CHEMINFORM, Issue 12 2010Ramon Badorrey Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Diversity in Gold- and Silver-Catalyzed Cycloisomerization of Epoxide,Alkyne Functionalities.CHEMINFORM, Issue 12 2009Guan-You Lin Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: An Efficient Method for the Ring Opening of Epoxide with Aromatic Amines by Sb(III) Chloride under Microwave Irradiation.CHEMINFORM, Issue 41 2008Dadkhoda Ghazanfari Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Ruthenium-Catalyzed Cyclization of Epoxide with a Tethered Alkyne: Formation of Ketene Intermediates via Oxygen Transfer from Epoxides to Terminal Alkynes.CHEMINFORM, Issue 39 2004Reniguntala J. Madhushaw Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Site-Selective DNA Alkylation of GG Steps by Naphthaldiimide Derivatives Possessing Enantiomeric Epoxide.CHEMINFORM, Issue 5 2001Akimitsu Okamoto Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Autoxidation of linalyl acetate, the main component of lavender oil, creates potent contact allergensCONTACT DERMATITIS, Issue 1 2008Maria Sköld Background:, Fragrances are among the most common causes of allergic contact dermatitis. We have in previous studies shown that linalool, present in lavender oil, autoxidizes on air exposure, forming allergenic oxidation products. Oxidized linalool was found to be a frequent cause of contact allergy in a patch test study on consecutive dermatitis patients. Linalyl acetate, the main component of lavender oil is commonly used as a fragrance chemical in scented products. Because of structural similarities, linalyl acetate should also be susceptible to oxidation on air exposure, forming similar oxidation products as linalool. Objective:, The aim of the present study was to investigate the autoxidation of linalyl acetate and the influence of oxidation on its sensitizing potency. Methods:, Analyses were performed using gas chromatography, nuclear magnetic resonance spectrometry and mass spectrometry. Sensitizing potencies of compounds were determined using the local lymph node assay (LLNA) in mice. Results:, Analyses showed that the content of linalyl acetate decreased over time on air exposure and other compounds were formed. Hydroperoxides, an epoxide and an alcohol were identified as oxidation products from linalyl acetate. In the LLNA, linalyl acetate of high purity showed a weak sensitizing potency (EC3 25%). Autoxidation increased the sensitizing potency of linalyl acetate, and a 10 weeks oxidized sample gave an EC3 value of 3.6%. As for linalool, the hydroperoxides were shown to be the oxidation products with the highest sensitizing potency. Conclusion:, It is concluded that autoxidation of the weakly allergenic linalyl acetate leads to formation of allergenic oxidation products. [source] Allergic contact dermatitis from cycloaliphatic epoxide in jet aviation hydraulic fluidCONTACT DERMATITIS, Issue 1 2001Howard I. Maibach [source] Removal of benzo(a)pyrene diol epoxide (BPDE)-DNA adducts as a measure of DNA repair capacity in lymphoblastoid cell lines from sisters discordant for breast cancerENVIRONMENTAL AND MOLECULAR MUTAGENESIS, Issue 2 2002Grazyna Motykiewicz Abstract The mutagen sensitivity assay is one of the approaches used to investigate individual DNA repair capacity. This method is based on the premise that after in vitro treatment with a test mutagen, DNA from subjects with defective repair will be more damaged than DNA from those with an efficient repair system. However, very little is known about unmeasured processes that occur between cell treatment and final assessment of DNA damage. To develop a more precise assay, we modified the traditional mutagen sensitivity assay to also include measurement of DNA damage after culturing cells in the absence of mutagen. First, we treated apparently normal and xeroderma pigmentosum lymphoblastoid cell lines with various doses of benzo(a)pyrene diol epoxide (BPDE) and harvested cells at different time points. A polyclonal antiserum against BPDE-DNA was used to quantitate levels of adducts by immunoslot-blot and immunohistochemistry. Selected conditions included treatment with 10 ,M BPDE, a 4-hr culture in mutagen-free medium, and immunohistochemical measurement of BPDE-DNA adducts. The method was then applied in a pilot study to 50 lymphoblastoid lines from sisters discordant for breast cancer. There was no significant difference between cases and controls in the level of BPDE-DNA adducts in lymphoblasts harvested immediately after BPDE treatment. However, after a 4-hr culture in mutagen-free medium, the level of adducts was significantly higher (P = 0.006) among cases than in controls. There was a two-fold increase in mean adduct removal in lines from nonaffected as compared to affected sisters (44% and 22% decrease, respectively). DNA repair capacity was predictive of case status (P = 0.04) in logistic regression analysis. This method, which can be easily applied to large numbers of samples, should be useful in studies to investigate the role of DNA repair in cancer risk. Environ. Mol. Mutagen. 40:93,100, 2002. © 2002 Wiley-Liss, Inc. [source] Environmental factors affecting the levels of legacy pesticides in the airshed of Delaware and Chesapeake Bays, USAENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 9 2010Anubha Goel Abstract Organochlorine insecticides and their degradation products contribute to toxicity in Chesapeake Bay, USA, sediments and affect the reproductive health of avian species in the region; however, little is known of atmospheric sources or temporal trends in concentrations of these chemicals. Weekly air (n,=,265) and daily rain samples (n,=,494) were collected over 2000 to 2003 from three locations in the Delmarva Peninsula, USA. Pesticides were consistently present in the gas phase with infrequent detection in the particle phase. Hexachlorocyclohexanes (HCHs) and cis - and trans -chlordane were detected most frequently (95,100%), and cis - and trans -nonachlor, oxychlordane, heptachlor, heptachlor epoxide, dieldrin, and 1-chloro-4-[2,2-dichloro-1-(4-chlorophenyl)ethenyl]benzene (4,4,-DDE) were also detected frequently. The highest mean air concentrations were for dieldrin (60,84,pg/m3), ,-HCH (37,83,pg/m3), and 4,4,-DDE (16,80,pg/m3). Multiple regression analyses of air concentrations with temperature and wind conditions using modified Clausius-Clapeyron equations explained only 30 to 60% of the variability in concentration for most chemicals. Comparison of the air concentrations and enthalpy of air,surface exchange values at the three sites indicate sources of chlordanes and ,-HCH sources are primarily from long-range transport. However, examination of chlordane isomer ratios indicates some local and regional contributions, and ,-HCH, 4,4,-DDE, dieldrin, heptachlor, heptachlor epoxide, and oxychlordane also have local or regional sources, possibly from contaminated soils. Median rain sample volumes of 1 to 3 L led to infrequent detections in rain; however, average measured concentrations were 2 to 10 times higher than in the Great Lakes. Dissipation half-lives in air were well below 10 years for all chemicals and below published values for the Great Lakes except dieldrin, which did not decline during the sample period. Environ. Toxicol. Chem. 2010;29:1893,1906. © 2010 SETAC [source] Incorporation of a (Cyclopentadienyl)molybdenum Oxo Complex in MCM-41 and Its Use as a Catalyst for Olefin EpoxidationEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 24 2004Marta Abrantes Abstract The tricarbonyl complex [(,5 -C5H4 -COOMe)Mo(CO)3Cl] was prepared from the reaction of sodium (methoxycarbonyl)cyclopentadienide, (C5H4 -CO2Me)Na, with (Bu4N)[Mo(CO)5I]. Heating the ester with 3-(triethoxysilyl)propylamine gave the amide derivative {[,5 -C5H4 -CONH-C3H6Si(OEt)3]Mo(CO)3Cl}. The functionalised tricarbonyl complex was immobilised in the ordered mesoporous silica MCM-41 with a loading of 13 wt.-% Mo (1.4 mmol·g,1) by carrying out a grafting reaction in dichloromethane. Powder X-ray diffraction and nitrogen adsorption,desorption analysis indicated that the structural integrity of the support was preserved during the grafting and that the channels remained accessible, despite significant reductions in surface area, pore volume and pore size. The success of the coupling reaction was confirmed by 29Si and 13C (CP) MAS NMR spectroscopy. A supported dioxo complex of the type [(,5 -C5H4R)MoO2Cl] was subsequently prepared by oxidative decarbonylation of the tethered tricarbonyl complex using tert -butyl hydroperoxide (TBHP). The oxidised material is an active catalyst for the liquid phase epoxidation of cyclooctene with TBHP as the oxygen source. Similar catalytic results were obtained using the tethered tricarbonyl complex directly as a pre-catalyst since fast oxidative decarbonylation occurs under the reaction conditions used. For both systems, the desired epoxide was the only product and the initial activities were about 13 mol·molMo,1·h,1. The solid catalysts were recycled several times. Some activity was lost between the first and second runs but thereafter tended to stabilise. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Fluorinated Analogues of Amicetose and Rhodinose , Novel Racemic and Asymmetric RoutesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 7 2009Jonathan M. Percy Abstract Trifluoroethanol was converted into difluorinated (racemic) analogues of amicetose and rhodinose by metallated difluoroenol acetal chemistry, protection, release of the latent difluoromethyl ketone, stereoselective reduction and ozonolysis in acidic methanol. A fortuitous separation of diastereoisomers allowed the diastereoisomeric pyranoses to be obtained cleanly. Though reductive defluorination allowed a facile entry to the route, the corresponding monofluoro sugar analogues could not be separated. Instead, Sharpless asymmetric epoxidation followed by epoxide ring-opening with an unusual nucleophilic fluoride source allowed enantiomerically highly enriched and selectively protected fluorodiols to be obtained. Ozonolysis then afforded the methyl pyranosides, which could be transformed in a number of ways. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Efficient Total Synthesis of (,)-(3S,6R)-3,6-Dihydroxy-10-methylundecanoic AcidEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 2 2007Satyendra Kumar Pandey Abstract An efficient enantioselective synthesis of (,)-(3S,6R)-3,6-dihydroxy-10-methylundecanoic acid (1) from epichlorohydrin is described. The key steps include Jacobsen's HKR, Sharpless asymmetric dihydroxylation, regioselective opening of epoxide and cyclic sulfate. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Synthesis of a Benzolactone Collection using Click ChemistryEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 1 2007Jan Ritschel Abstract A collection of benzotriazoles consisting of seven compounds was prepared from the propynyl-substituted benzolactone 1 and various azides using click chemistry. The lactone 1 was obtained through a short route by direct esterification of the allylbenzoic acid 9 with the alkynol 7 giving the benzoate 2. The homopropargyl alcohol 7 in turn was obtained by opening the epoxide 6 with triisopropylsilyl acetylide. Ring-closing metathesis of the ester 2 using Grubbs catalyst II followed by removal of the silicon protecting group furnished the lactone 1. Two of the benzotriazoles, 17a and 17b, were also converted into the corresponding phenols to probe the role of the phenolic OH on the biological activity. All nine benzotriazoles showed cytotoxic activity in a L929 mouse fibroblast assay with IC50 values in the low micromolar range. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Oxidation of ,4 - and ,5 -Steroids with Hydrogen Peroxide Catalyzed by Porphyrin Complexes of MnIII and FeIIIEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 23 2004Susana L. H. Rebelo Abstract In this paper we describe a new environmentally friendly method to promote the stereoselective epoxidation of ,4 - and ,5 -steroids. Metalloporphyrins efficiently catalyze the epoxidation reactions of 17,-acetoxy-4-androstene (1), 4-cholestene (2) and 3,-acetoxy-5-cholestene (3) in the presence of H2O2 as oxygen donor. Modeling the molecular structure of the porphyrin as well as the central metal allows the control of the preferential formation of ,- or ,-epoxides. Porphyrins with bulky, electron-withdrawing groups in the ortho positions of the meso phenyls and with MnIII as the central metal ion, such as [Mn(TDCPP)Cl], gave preferentially the ,-epoxide of ,4 - and ,5 -steroids. [Fe(TPFPP)Cl] catalyzes preferentially the ,-epoxidation of ,4 -steroids and also increases the stereoselectivity for the ,-epoxide in ,5 -steroids, similar to the results obtained with m -CPBA (m -chloroperbenzoic acid) as oxidant. The substrate structure strongly influences the chemoselectivity of the reactions. The X-ray structures of two main products were determined, and two-dimensional NMR techniques allowed the full assignment of 1H and 13C NMR resonances as well as the stereochemistry of these products. A mechanistic proposal involving oxo species for the ,-approach and peroxy species for the ,-approach is proposed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Regioselective SN2 Opening of Vinylic Epoxides with Trialkylzincates and TrialkylaluminatesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 10 2004Olivier Equey Abstract The use of trialkylorganozincates and tetraalkylaluminates allows regioselective SN2 nucleophilic opening of vinylic epoxides. The reaction occurs with an anti -substitution pattern and can be applied to a wide range of substrates. We also show that the solvent and the structure of the epoxide have an influence on the substitution products' ratio. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Efficient Addition of Acid Enediolates to EpoxidesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 10 2004Salvador Gil Abstract We report new conditions to facilitate the addition of dianions of carboxylic acids to epoxides as an alternative method to the use of aluminum enolates. These conditions require the use of a sub-stoichiometric (10%) amount of amine for dianion generation and the previous activation of the epoxide with LiCl. Other Lewis acids have been shown to be less effective. Yields are good but only low diastereoselectivity is attained, which has not been controlled despite attempts at optimization. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Chemoenzymatic Synthesis of (2S)- and (2R)-2-(1,3-Dithian-2-ylmethyl)oxiraneEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2004Eirik Sundby Abstract Lipase-catalyzed transesterifications and biological reductions were used to obtain the (S)-enantiomers of 3-chloro-1-(1,3-dithian-2-yl)-2-propanol and 1-(1,3-dithian-2-yl)-3-fluoro-2-propanol and their (R)-acetates. (S)-3-Chloro-1-(1,3-dithian-2-yl)-2-propanol and (R)-3-chloro-1-(1,3-dithian-2-yl)-2-propyl acetate were converted into the respective enantiomers of 2-(1,3-dithian-2-ylmethyl)oxirane. During this work we also isolated a new gem -disubstituted epoxide, 2-(chloromethyl)-2-(1,3-dithian-2-yl)oxirane. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Differential mechanism-based labeling and unequivocal activity assignment of the two active sites of intestinal lactase/phlorizin hydrolaseFEBS JOURNAL, Issue 24 2000Juan C. Díaz Arribas Milk lactose is hydrolysed to galactose and glucose in the small intestine of mammals by the lactase/phlorizin hydrolase complex (LPH; EC 3.2.1.108/62). The two enzymatic activities, lactase and phlorizin hydrolase, are located in the same polypeptide chain. According to sequence homology, mature LPH contains two different regions (III and IV), each of them homologous to family 1 glycosidases and each with a putative active site. There has been some discrepancy with regard to the assignment of enzymatic activity to the two active sites. Here we show differential reactivity of the two active sites with mechanism-based glycosidase inhibitors. When LPH is treated with 2,,4,-dinitrophenyl 2-deoxy-2-fluoro-,- d -glucopyranoside (1) and 2,,4,-dinitrophenyl-2-deoxy-2-fluoro-,- d -galactopyranoside (2), known mechanism-based inhibitors of glycosidases, it is observed that compound 1 preferentially inactivates the phlorizin hydrolase activity whereas compound 2 is selective for the lactase active site. On the other hand, glycals (d -glucal and d -galactal) competitively inhibit lactase activity but not phlorizin hydrolase activity. This allows labeling of the phlorizin site with compound 1 by protection with a glycal. By differential labeling of each active site using 1 and 2 followed by proteolysis and MS analysis of the labeled fragments, we confirm that the phlorizin hydrolysis occurs mainly at the active site located at region III of LPH and that the active site located at region IV is responsible for the lactase activity. This assignment is coincident with that proposed from the results of recent active-site mutagenesis studies [Zecca, L., Mesonero, J.E., Stutz, A., Poiree, J.C., Giudicelli, J., Cursio, R., Gloor, S.M. & Semenza, G. (1998) FEBS Lett.435, 225,228] and opposite to that based on data from early affinity labeling with conduritol B epoxide [Wacker, W., Keller, P., Falchetto, R., Legler, G. & Semenza, G. (1992) J. Biol. Chem.267, 18744,18752]. [source] Character impact odorants from wild mushroom (Lactarius hatsudake) used in Japanese traditional foodFLAVOUR AND FRAGRANCE JOURNAL, Issue 4 2010Mitsuo Miyazawa Abstract The components of the volatile oil from wild mushroom (Lactarius hatsudake), used in Japanese traditional food, were analysed and quantified for the first time by capillary GC and GC,MS. Seventy-six components were separated from the oil and of these 71 components were identified. The main components of the oil were oxidized sesquiterpenes [cis -isolongifolanone (624.9,,g/100,g), , -cedrene epoxide (578.7,,g/100,g), humulene epoxide III (453.9,,g/100,g), clovane (425.4,,g/100,g)], aliphatic acids [linoleic acid (585.9,,g/100,g) and palmitoleic acid (333.3,,g/100,g)]. Odour evaluation of the volatile oil from L. hatsudake was also carried out using GC,MS/olfactometry (GC,MS/O) and aroma extract dilution analysis (AEDA), from which it was found that hexanal, 4-dehydroviridiflorol, myliol and phenylacetaldehyde seem to contribute to the green, spicy and sweet odour of L. hatsudake. Copyright © 2010 John Wiley & Sons, Ltd. [source] Synthesis of Some Novel Thioxanthenone-Fused Azacrown Ethers, and Their Use as New Catalysts in the Efficient, Mild, and Regioselective Conversion of Epoxides to , -Hydroxy Thiocyanates with Ammonium ThiocyanateHELVETICA CHIMICA ACTA, Issue 7 2007Hashem Sharghi Abstract The regioselective ring-opening reactions of some epoxides with ammonium thiocyanate in the presence of a series of new 9H -thioxanthen-9-one-fused azacrown ethers, i.e., 7,11 (Scheme,1), and also of dibenzo[18]crown-6 (12), Kryptofix®22 (13), and benzo[15]crown-5 (14) were studied (Tables 1 and 2). The epoxides were subjected to cleavage by NH4SCN in the presence of these catalysts under mild conditions in various aprotic solvents. Reagents and conditions were identified for the synthesis of individual , -hydroxy thiocyanates in high yield and with more than 90% regioselectivity. The results can be discussed in terms of a four-step mechanism (Scheme,2): 1) formation of a complex between catalyst and NH4SCN, 2) release of SCN, from the complex, 3) reaction of the released SCN, at the sterically less hindered site of the epoxide, and 4) regeneration of the catalyst. The major advantages of this method are the high regioselectivity, the simple regeneration of the catalyst, the reuse of it through several cycles without a decrease of activity, and the ease of workup of the reaction mixtures. [source] Reactions of Allyl Alcohols of the Pinane Series and of Their Epoxides in the Presence of Montmorillonite ClayHELVETICA CHIMICA ACTA, Issue 2 2007Irina Abstract The reactivity of allyl alcohols of the pinane series and of their epoxides in the presence of montmorillonite clay in intra- and intermolecular reactions was studied. Mutual transformations of (+)- trans -pinocarveol ((+)- 2) and (,)-myrtenol ((,)- 3a) were major reactions of these compounds on askanite,bentonite clay (Schemes,1 and 2). However, the two reactions gave different isomerization products, indicating that the reactivity of the starting alcohol (+)- 2 or (,)- 3a was different from that of the same compound (+)- 2 or (,)- 3 formed in the course of the reactions. (,)- cis - and (+)- trans -Verbenol ((,)- 16 and (+)- 12, resp.), as well as (,)- cis -verbenol epoxide ((,)- 20) reacted with both aliphatic and aromatic aldehydes on askanite,bentonite clay giving various heterocyclic compounds (Schemes,4, 5 and 7); the reaction path depended on the structure of both the terpenoid and the aldehyde. [source] Lewis Basic Ionic Liquids-Catalyzed Conversion of Carbon Dioxide to Cyclic CarbonatesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2010Zhen-Zhen Yang Abstract A series of easily prepared Lewis basic ionic liquids were developed for cyclic carbonate synthesis from epoxide and carbon dioxide at low pressure without utilization of any organic solvents or additives. Notably, quantitative yields together with excellent selectivity were attained when 1,8-diazabicyclo[5.4.0]undec-7-enium chloride ([HDBU]Cl) was used as a catalyst. Furthermore, the catalyst could be recycled over five times without appreciable loss of catalytic activity. The effects of the catalyst structure and various reaction parameters on the catalytic performance were investigated in detail. This protocol was found to be applicable to a variety of epoxides producing the corresponding cyclic carbonates in high yields and selectivity. Therefore, this solvent-free process thus represents an environmentally friendly example for the catalytic conversion of carbon dioxide into value-added chemicals by employing Lewis basic ionic liquids as catalyst. A possible catalytic cycle for the hydrogen bond-assisted ring-opening of epoxide and activation of carbon dioxide induced by the nucleophilic tertiary nitrogen of the ionic liquid was also proposed. [source] Grafting of Molecularly Ordered Mesoporous Phenylene-Silica with Molybdenum Carbonyl Complexes: Efficient Heterogeneous Catalysts for the Epoxidation of OlefinsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010Abstract Arenetricarbonyl complexes, or the general formula C6H4Mo(CO)3, were incorporated into crystal-like mesoporous phenylene-silica by liquid-phase deposition of molybdenum hexacarbonyl [Mo(CO)6]. By adjusting the reaction conditions, different molybdenum loadings of 1.5 and 5.9,wt% were obtained, which correspond to 3% and 14% of the phenylene contents. The texture properties of the materials as well as the nature of the surface-fixed complexes were characterized by powder X-ray diffraction, transmission electron microscopy (TEM), N2 adsorption, FT-IR, UV-vis and MAS (13C, 29Si) NMR spectroscopy. The derivatized organosilicas were examined as catalyst precursors for the liquid-phase epoxidation of cis -cyclooctene, 1-octene, trans -2-octene and (R)-(+)-limonene at 55,°C, using tert -butyl hydroperoxide as the oxidant. For each olefin the corresponding epoxide was the only product detected. In the case of cyclooctene, the intrinsic reaction rates per surface molybdenum atom were similar for both Mo loadings (TOF,1150 mol,molMo,1,h,1), suggesting that the resultant materials act as single site epoxidation catalysts. Leaching tests and metal analyses of reaction solutions showed that the catalytic activity stemmed from the immobilized species and not from the leaching of active species into solution. The oxidation of limonene gave limonene oxide as the only product in 95% yield at 3,h, which reveals an outstanding regioselectivity to the epoxidation of the endocyclic double bond. [source] Immobilization of Porphyrinatocopper Nanoparticles onto Activated Multi-Walled Carbon Nanotubes and a Study of its Catalytic Activity as an Efficient Heterogeneous Catalyst for a Click Approach to the Three-Component Synthesis of 1,2,3-Triazoles in WaterADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2009Hashem Sharghi Abstract An efficient, regioselective, one-pot and two-step synthesis of ,-hydroxy 1,4-disubstituted 1,2,3-triazoles from a wide range of non-activated terminal alkynes and epoxides and sodium azide by way of a three-component click reaction using a catalytic amount of [meso -tetrakis(o -chlorophenyl)porphyrinato]copper(II) (5,mol%) in excellent isolated yields is described. The reactions were performed in water as a green solvent at ambient temperature without any additives. By performing two reaction steps in one pot and purifying only at the final step, this procedure excludes any interim purification of in situ generated organic azide intermediates, which significantly improves the overall yield and reduces the reaction time. To benefit from the recovery and reuse of the catalyst, a new heterogeneous catalyst was prepared by simple and successful impregnation of the catalyst onto activated multi-walled carbon nanotubes (AMWCNT). The heterogeneous catalyst was characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic forced microscopy (AFM), and thermogravimetric (TG) analysis to estimate the amount of nitrogen adsorption, and Raman and FT-IR spectroscopy. Leaching experiments after ten successive cycles showed that the catalyst is most strongly anchored to the AMWCNT support. Mechanistically, porphyrinatocopper catalyzes each step of the reaction in different ways as a bifunctional catalyst including epoxide ring opening by azide delivery to epoxide, forming in situ generated 2-azido alcohols followed by activation of the CC triple bond of the starting terminal alkynes by forming a porphyrinatocopper-acetylide intermediate and thereby promoting the [3+2]-cycloaddition reaction as the key step to form the triazole framework. [source] Porous epoxies by reaction induced phase separation of removable alcohols: Control of spheroidal pore size by mass fraction, cure temperature, and reaction rate,JOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010Robert J. Klein Abstract Porous organic and inorganic materials with both random and controlled microstructures have utility in a variety of fields including catalysis, sensors, separations, optical platforms, tissue engineering, hydrogen storage, micro-electronics, medical diagnostics, as well as other applications. This work highlights a simple and general technique for tuning the pore size in crosslinking polymeric systems by adding a solvent poragen that phase separates during the curing process (reaction induced phase separation). The pore size can be controlled over large length scales ranging from microns to well below 100 nanometers. In this system an amine cured epoxy resin was reacted in the presence of the sacrificial poragen octadecanol, which is removed by vacuum-assisted evaporation once the epoxy components have reacted to form a solid, porous matrix. The importance of the present approach is based on the simplicity of the chemical formulation, the ease by which other epoxide or amine chemistries may be substituted for the two reactive components, and the control of pore size down to the nanometer scale by the addition of a small amount of catalyst. © 2010 Wiley Periodicals, Inc., J Appl Polym Sci, 2010 [source] Nonisothermal cure kinetics of DGEBA with novel aromatic diamineJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2007M. Ghaemy Abstract The effect of the molar ratio of diglycidyl ether of a bisphenol-A based epoxy (DGEBA) and synthesized 4-phenyl-2,6-bis(4-aminophenyl)pyridine (PAP) as curing agent during nonisothermal cure reaction by the Kissinger, Ozawa, and isoconversional equations was studied. The cure mechanism was studied by FTIR analysis. Kinetic analysis of the curing reaction of DGEBA at two different concentrations (42 and 32 phr) of the curing agent was studied by using DSC analysis. With an increasing PAP content, the pre-exponential factor increased by increasing collision probability between epoxide and primary or secondary amine groups in noncataltyic or catalytic modes. The activation energy also increased because of the increasing content of crosslink density. The activation energies obtained from three equations were in good agreement. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3076,3083, 2007. [source] The role of calcium in apoptosis induced by 7,-hydroxycholesterol and cholesterol-5,,6,-epoxideJOURNAL OF BIOCHEMICAL AND MOLECULAR TOXICOLOGY, Issue 5 2009Sinéad Lordan Abstract Oxysterols, such as 7,-hydroxy-cholesterol (7,-OH) and cholesterol-5,,6,-epoxide (,-epoxide), may have a central role in promoting atherogenesis. This is thought to be predominantly due to their ability to induce apoptosis in cells of the vascular wall and in monocytes/macrophages. Although there has been extensive research regarding the mechanisms through which oxysterols induce apoptosis, much remains to be clarified. Given that experimental evidence has long associated alterations of calcium (Ca2+) homeostasis to apoptotic cell death, the aim of the present study was to determine the influence of intracellular Ca2+ changes on apoptosis induced by 7,-OH and ,-epoxide. Ca2+ responses in differentiated U937 cells were assessed by epifluorescence video microscopy, using the ratiometric dye fura-2. Over 15-min exposure of differentiated U937 cells to 30 ,M of 7,-OH induced a slow but significant rise in fura-2 ratio. The Ca2+ channel blocker nifedipine and the chelating agent EGTA blocked the increase in cytoplasmic Ca2+. Moreover, dihydropyridine (DHP) binding sites identified with BODIPY-FLX-DHP were blocked following pretreatment with nifedipine, indicating that the influx of Ca2+ occurred through L-type channels. However, following long-term incubation with 7,-OH, elevated levels of cytoplasmic Ca2+ were not maintained and nifedipine did not provide protection against apoptotic cell death. Our results indicate that the increase in Ca2+ may be an initial trigger of 7,-OH,induced apoptosis, but following chronic exposure to the oxysterol, the influence of Ca2+ on apoptotic cell death appears to be less significant. In contrast, Ca2+ did not appear to be involved in ,-epoxide,induced apoptosis. © 2009 Wiley Periodicals, Inc. J Biochem Mol Toxicol 23:324,332, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20295 [source] Heterogeneity of the coumarin anticoagulant targeted vitamin K epoxide reduction system.JOURNAL OF BIOCHEMICAL AND MOLECULAR TOXICOLOGY, Issue 5 2006Study of kinetic parameters in susceptible, resistant mice (Mus musculus domesticus) Abstract Vitamin K epoxide reductase (VKOR) activity in liver microsomes from a susceptible and a genetically warfarin-resistant strain of mice (Mus Musculus domesticus) was analyzed to determine the mechanism of resistance to this 4-hydroxycoumarin derivative. Kinetic parameters for VKOR were calculated for each strain by incubating liver microsomes with vitamin K epoxide ± warfarin. In susceptible mice, an Eadie,Hofstee plot of the data was not linear and suggested the involvement of at least two different components. Apparent kinetic parameters were obtained by nonlinear regression using a Michaelis--Menten model, which takes into account two enzymatic components. Component A presents a high Km and a high Vm, and as a consequence only an enzymatic efficiency Vm/Km was obtained (0.0024 mL/min/mg). Estimated warfarin Ki was 0.17 ,M. Component B presented an apparent Km of 12.73 ,M, an apparent Vm of 0.32 nmol/min/mg, and an apparent Ki for warfarin of 6.0 ,M. In resistant mice, the enzymatic efficiency corresponding to component A was highly decreased (0.0003,0.00066 mL/min/mg) while the Ki for warfarin was not modified. The apparent Vm of component B was poorly modified between susceptible and resistant mice. The apparent Km of component B observed in resistant mice was similar to the Km observed in susceptible mice. These modifications of the catalytic properties are associated with a single nucleotide polymorphism (T175G) in the VKOR-C1 gene, which corresponds to a Trp59Gly mutation in the protein. © 2006 Wiley Periodicals, Inc. J Biochem Mol Toxicol 20:221,229, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20144 [source] Synthesis of [14C]-radiolabelled entecavirJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 9 2005Marc D. Ogan Abstract Radiolabelled [14C]entecavir, (1), was prepared in 12 steps from (1S,2R,3S,5R)-3-(benzyloxy)-2-(benzyloxymethyl)-6-oxa-bicyclo[3.1.0]hexane 2. The chemical yield of [14C]entecavir was 14% from the epoxide 2. Introduction of [14C] radiolabel was achieved by elaboration of 4,5-diaminopyrimidine 8 with triethyl[14C]orthoformate to purine derivative 9. The radiochemical yield of [14C]entecavir from triethyl[14C]orthoformate was 11.3%. Radiochemical purity of [14C]entecavir determined by HPLC was 99.8%. The specific activity of [14C]entecavir was 108 µCi/mg (29.9 mCi/mmol). Copyright © 2005 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||||||||||||||