Home About us Contact
|
Home About us Contact | ||
|
|
||
Ethyl N (ethyl + n)
Selected AbstractsChemInform Abstract: The 1,3-Dipolar Cycloaddition of Ethyl N-(Ethoxycarbonylmethyl)benzimidate with N-Aryl Maleimides.CHEMINFORM, Issue 39 2001Ji-Jun Chen 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] Solubility, salivary sorption and degree of conversion of dimethacrylate-based polymeric matrixesJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2008Luana Gonçalves Abstract This study investigated the relationship between the solubility, salivary sorption, and degree of conversion of dimethacrylate-based polymeric matrixes. Six polymeric matrixes produced by mixing bis-GMA, TEGDMA and UDMA dimethacrylate monomers were studied. Photoactivation was induced by camphoroquinone/ethyl N,N-dimethyl-4-aminobenzoate. The specimens were light-cured using an irradiance of 850 mW/cm2 for 20 s. The solubility and sorption (,g/mm3) were measured after immersion in artificial saliva (neutral pH) for 7 days. The degree of conversion (%) was obtained by using a FT-IR spectrometer equipped with an attenuated total reflectance crystal (ATR). The degree of conversion varied from 39.15 ± 6.30 to 65.57± 4.80, and was influenced by the viscosity of the monomers present in the polymeric matrixes. The solubility of polymeric matrixes varied between 13.64 ± 0.39 and 25.08 ± 0.83, and was strongly influenced by the degree of conversion (Pearson, r = ,0.9587, p < 0.01). No correlation was found between salivary sorption and the degree of conversion (p = 0.3918). Salivary sorption was only dependent on the chemical and physical structures of the monomers presented in the polymeric matrixes. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2008 [source] Novel Spiroheterocycles by Aziridination of ,-Methylene-,- and -,-lactamsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 14 2007M. Antonietta Loreto Abstract New potentially bioactive ,-spiroaziridino-,- and -,-lactams have been prepared by treatment of ,-methylene-,- and -,-lactams with ethyl N -{[(4-nitrophenyl)sulfonyl]oxy}carbamate (NsONHCO2Et) in the presence of CaO. These compounds, through reductive aziridine ring opening, can be intermediates for the synthesis of ,- and ,-aminolactams, which are useful as conformational constraints in peptides. The above procedure has been successfully extended to one ,-methyleneoxindole to obtain a new spirooxindole derivative, a potential precursor of natural alkaloids. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Synthesis of the Antibiotic (R)-Reutericyclin via Dieckmann CondensationHELVETICA CHIMICA ACTA, Issue 11 2005Roswitha Böhme (R)-Reutericyclin ((R)- 1), a bactericidal, amphiphilic natural product with a trisubstituted tetramic acid moiety, was prepared in four steps from D -leucine in an overall yield of 24%. The chiral heterocyclic portion of 1 was synthesized by Dieckmann cyclization of ethyl N -(acetoacetyl)leucinate (7), and the resulting pyrrole derivative 8 was N -acylated with (E)-dec-2-enoyl chloride in the presence of BuLi at ,,70° (Scheme,2). This new procedure is straightforward and allows the synthesis of both antipodes of reutericyclin in an enantiomeric excess (ee) of ca. 80%. [source] Synthesis of Scopin Acetate and 6,7-Didehydrohyoscyamin.HELVETICA CHIMICA ACTA, Issue 9 2003Intramolecular Phenylsulfenylation of a Nonactivated Methylene Group of Ethyl N -Demethyl-3- O -(phenylthio)tropine- N -carboxylate The synthesis of scopin acetate (6b) and 6,7-didehydrohyoscyamine (17) was achieved by using tropine (5) as the starting compound. Formal (phenylthio)-radical transfer to the nonactivated 6-position of ethyl N -demethyl-3- O -(phenylthio)tropine- N -carboxylate (9) by irradiation in the presence of hexabutyldistannane is a key step of this synthetic approach, involving ethyl 6,7-didehydro- N -demethyltropine- N -carboxylate (15) as a synthetic intermediate (Schemes,3 and 5). The reaction of 9 with tributylstannane in the presence of ethyl acrylate, as a radicophilic olefin, involves Michael -type alkylation at C(6) of the tropine skeleton affording ethyl N -demethyl- N -(ethoxycarbonyl)tropine-6-propanoate (18) (Scheme,6). [source] Kinetics and mechanism for the formation of o -carboxy(N -methyl)-benzohydroxamic acid in the cleavage of ethyl N -[o -(N -methyl- N -hydroxycarbamoyl)-benzoyl]carbamate in N -methylhydroxylamine, acetate, and phosphate buffersINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 9 2003M. Niyaz Khan The rate of cleavage of ethyl N -[o -(N -methyl- N -hydroxycarbamoyl)benzoyl]- carbamate (ENMBC) in the buffer solutions containing N -methylhydroxylamine, acetate + N -methylhydroxylamine, and phosphate + N -methylhydroxylamine followed an irreversible consecutive reaction path: ENMBC where A and B represent N -hydroxyl group cyclized product of ENMBC and o -(N -methyl- N -hydroxycarbamoyl)benzoic acid, respectively. Both rate constants k1 obs and k2 obs showed the presence of buffer catalysis, but buffer catalysis turned out to be weak in the presence N -methylhydroxylamine buffer, while it was strong in the presence of acetate and phosphate ones. Buffer-independent rate constants k10 and k20 increased linearly with the increase in aOH with definite intercepts. The values of molar absorption coefficient of A, obtained under varying total buffer concentrations at a constant pH, showed the presence of a fast equilibrium: A + CH3NHOH , C, where C represents N -[o -(N -methyl- N -hydroxycarbamoyl)methyl]benzohydroxamic acid. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 427,437, 2003 [source] Kinetic evidence for the occurrence of kinetically detectable intermediates in the cleavage of N -ethoxycarbonylphthalimide under N -methylhydroxylamine buffersINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 2 2002M. Niyaz Khan The kinetics of the aqueous cleavage of N -ethoxycarbonylphthalimide (NCPH) in CH3NHOH buffers of different pH reveals that the cleavage follows the general irreversible consecutive reaction path NCPH ENMBC AB, where ENMBC, A, and B represent ethyl N -[o -(N -methyl- N -hydroxycarbamoyl)benzoyl]carbamate, N -hydroxyl group cyclized product of ENMBC, and o -(N -methyl- N -hydroxycarbamoyl)benzoic acid, respectively. The rate constant k1 obs at a constant pH, obeys the relationship k1 obs = kw + knapp [Am]T + kb[Am]T2, where [Am]T is the total concentration of CH3NHOH buffer and kw is first-order rate constant for pH-independent hydrolysis of NCPH. Buffer-dependent rate constant kb shows the presence of both general base and general acid catalysis. Both the rate constants k2 obs and k3 obs are independent of [Am]T (within the [Am]T range of present study) at a constant pH and increase linearly with the increase in aOH with definite intercepts. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 95,103, 2002 [source] Effects of entropy on the gas-phase pyrolysis of ethyl N,N -dimethylcarbamateJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 3 2007Chang K. Kim Abstract In this study, we examined the gas-phase pyrolysis of ethyl N,N -dimethylcarbamate theoretically at various theoretical levels. The reaction consists of a two-step mechanism, with N,N -dimethylcarbamic acid and ethylene as reaction intermediates. In the first step, the reaction proceeds via a six-membered cyclic transition state (TS), which is more favorable than that via a four-membered cyclic TS. Here, the contribution of entropy to the overall potential energy surface was found to play an important role in determining the rate-limiting step, which was found to be the second step when viewed in terms of the enthalpy of activation (,H,), but the first step when entropy changes (,T,S,) were considered. These results are consistent with experimental findings. Moreover, the experimental activation entropy can be reproduced by using the hindered rotor approximation, which converts some low vibration frequencies that correspond to internal rotational modes into hindered rotors. © 2006 Wiley Periodicals, Inc. J Comput Chem 28: 625,631, 2007 [source] Synthesis of nitrogen-containing heterocycles 9,.JOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 6 2000- a][, Preparation, ]-triazolo[, ]triazine] derivatives, carbon-carbon bond cleavage of spiro[cycloalkane[, related compounds Diaminomethylenehydrazones of cyclic ketones 1,5 reacted with ethyl N -cyanoimidate (I) at room temperature or with bis(methylthio)methylenecyanamide (II) under brief heating to give directly the corresponding spiro[cycloalkane[1,,2,,4,]triazolo[1,,5,,- a][1,,3,-5,]triazine] derivatives 7,12 in moderate to high yields. Ring-opening reaction of the spiro[cycloalkanetriazolotriazine] derivatives occurred at the cycloalkane moiety upon heating in solution to give 2-alkyl-5-amino[1,2,4]triazolotriazines 13,16. Diaminomethylenehydrazones 17,19, of hindered acyclic ketones, gave 2-methyl-7-methylthio[1,2,4]-triazolo[1,5- a][1,3,5]triazines 21,23 by the reaction with II as the main products with apparent loss of 2-methylpropane from the potential precursor, 2- tert -butyl-2-methyl-7-methylthio[1,2,4]triazolo[1,5- a]-[1,3,5]triazines 20, in good yields. In general, bis(methylthio)methylenecyanamide II was found to be a favorable reagent to the one-step synthesis of the spiro[cycloalkanetriazolotriazine] derivatives from the diaminomethylenehydrazones. The spectral data and structural assignments of the fused triazine products are discussed. [source] Desorption electrospray ionization mass spectrometric analysis of organophosphorus chemical warfare agents using ion mobility and tandem mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 11 2010Paul A. D'Agostino Desorption electrospray ionization mass spectrometry (DESI-MS) has been applied to the direct analysis of sample media for target chemicals, including chemical warfare agents (CWA), without the need for additional sample handling. During the present study, solid-phase microextraction (SPME) fibers were used to sample the headspace above five organophosphorus CWA, O -isopropyl methylphosphonofluoridate (sarin, GB), O -pinacolyl methylphosphonofluoridate (soman, GD), O -ethyl N,N -dimethyl phosphoramidocyanidate (tabun, GA), O -cyclohexyl methylphosphonofluoridate (cyclohexyl sarin, GF) and O -ethyl S-2-diisopropylaminoethyl methyl phosphonothiolate (VX) spiked into glass headspace sampling vials. Following sampling, the SPME fibers were introduced directly into a modified ESI source, enabling rapid and safe DESI of the toxic compounds. A SYNAPT HDMSÔ instrument was used to acquire time-aligned parallel (TAP) fragmentation data, which provided both ion mobility and MSn (n,=,2 or 3) data useful for the confirmation of CWA. Unique ion mobility profiles were acquired for each compound and characteristic product ions of the ion mobility separated ions were produced in the TriwaveÔ transfer collision region. Up to six full scanning MSn spectra, containing the [M,+,H]+ ion and up to seven diagnostic product ions, were acquired for each CWA during SPME fiber analysis. A rapid screening approach, based on the developed methodology, was applied to several typical forensic media, including Dacron sampling swabs spiked with 5,µg of CWA. Background interference was minimal and the spiked CWA were readily identified within one minute on the basis of the acquired ion mobility and mass spectrometric data. Copyright © 2010 Crown in the right of Canada. Published by John Wiley & Sons, Ltd. [source] Hydrogen-bonding patterns in two aroylthiocarbamates and two aroylimidothiocarbonatesACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2010Henry Insuasty In O -ethyl N -benzoylthiocarbamate, C10H11NO2S, the molecules are linked into sheets by a combination of two-centre N,H...O and C,H...S hydrogen bonds and a three-centre C,H...(O,S) hydrogen bond. A combination of two-centre N,H...O and C,H...O hydrogen bonds links the molecules of O -ethyl N -(4-methylbenzoyl)thiocarbamate, C11H13NO2S, into chains of rings, which are linked into sheets by an aromatic ,,, stacking interaction. In O,S -diethyl N -(4-methylbenzoyl)imidothiocarbonate, C13H17NO2S, pairs of molecules are linked into centrosymmetric dimers by pairs of symmetry-related C,H...,(arene) hydrogen bonds, while the molecules of O,S -diethyl N -(4-chlorobenzoyl)imidothiocarbonate, C12H14ClNO2S, are linked by a single C,H...O hydrogen bond into simple chains, pairs of which are linked by an aromatic ,,, stacking interaction to form a ladder-type structure. [source] Crystallization of a carbamatase catalytic antibody Fab fragment and its complex with a transition-state analogueACTA CRYSTALLOGRAPHICA SECTION D, Issue 1 2004Carbamatase catalytic antibody Fab fragment Catalytic antibodies showing carbamatase activity have significant potential in antibody-directed prodrug therapy against tumours. The Fab fragment of an IgG1 mouse monoclonal carbamatase catalytic antibody JC1 raised against a transition-state analogue, ethyl N -(3,5-dicarboxyphenyl)- P -{N- [5,-(2,,,5,,-dioxo-1,,-pyrrolidinyl)oxy-1,,5,-dioxopentyl]-4-aminophenylmethyl}phosphonamidate, was obtained by digestion of the whole antibody with papain and was purified by two-step ion-exchange chromatography. Using hanging-drop vapour-diffusion crystallization techniques, three different crystal forms of the Fab fragment were obtained in the presence and absence of the transition-state analogue. All crystals diffract X-rays to between 3.5 and 3.2,Å resolution. The two crystal forms grown in the presence of the transition-state analogue contain up to four or eight copies of the Fab in the asymmetric unit and diffract to 3.5 and 3.2,Å, respectively. The crystal of the Fab alone is most likely to contain only two copies of the Fab in the asymmetric unit and diffracts to beyond 3.5,Å. Determination of the structure will provide insights into the active-site arrangement of this antibody and will help to increase our understanding of the molecular mechanisms by which the immune system can evolve catalytic function. [source] | ||||||||||||||||||||||