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191.
The reactions of 1,1-diacetylcyclopropane (1) with a number of hydrazine and hydroxylamine derivatives proceed via cyclopropane ring opening with incorporation of external nucleophile (solvent) to give the 4-β-X-ethyl derivatives of 3,5-dimethylpyrazoles and -isoxazoles, a novel route to these heterocycles. This ring cleavage occurs especially smoothly in water as a solvent. A rationale for this unusually mild nucleophilic cyclopropane ring opening is discussed. 相似文献
192.
McCoy LF Scholl PF Schleicher RL Groopman JD Powers CD Pfeiffer CM 《Rapid communications in mass spectrometry : RCM》2005,19(16):2203-2210
A method for quantitative analysis of aflatoxin B1-lysine adduct (B1-Lys) in serum by liquid chromatography using tandem mass spectrometry (LC/MS/MS) is presented. The protein in a 250-microL sample was digested in the presence of a stable-isotope internal standard during a 4-h incubation at 37 degrees C with Pronasetrade mark. B1-Lys and the internal standard were extracted using mixed-mode solid-phase extraction cartridges and eluted with 2% formic acid in methanol. Following evaporation and reconstitution, extracts were injected onto a Luna C-18(2) column and eluted with a step gradient of acetonitrile and 0.06% formic acid. The B1-Lys and the internal standard were detected in a positive ionization selective reaction monitoring mode with a ThermoFinnigan TSQ Quantum triple quadrupole mass spectrometer. Calibration curves were linear for concentrations from 0.05-8.0 ng/mL. The method was validated with aflatoxin B1 dosed rat serum diluted to anticipated high and low concentrations. Total imprecision determined from 30 measurements over 15 days was 5.6% and 9.1%, respectively. Recoveries of 78.8 +/- 6.4% for B1-Lys and 85.4 +/- 12.4% for the internal standard were based on the full extraction and reconstitution processes. The method can be used to quantitate B1-Lys at the 0.5 pg/mg albumin level and is suitable for routine analysis. 相似文献
193.
Nina K Gusarova Svetlana I ShaikhudinovaSvetlana N Arbuzova Tamara I Vakul'skayaBoris G Sukhov Lidiya M SinegovskayaMikhail V Nikitin Anastasiya G Mal'kinaNataliya A Chernysheva Boris A Trofimov 《Tetrahedron》2003,59(26):4789-4794
Primary and secondary phosphines add regio- and stereospecifically to phenylcyanoacetylene and 4-hydroxy-4-methylpent-2-ynenitrile under mild conditions to form corresponding functionalized secondary and tertiary phosphines of Z-configuration in 70-91% yield. According to ESR and UV data, the addition of primary phosphines to phenylcyanoacetylene involves a single electron transfer process. 相似文献
194.
Edisher G. Kvesitadze Tamara B. Lomitashvili Maia P. Khutsishvili Raphael Lamed Edward A. Bayer 《Applied biochemistry and biotechnology》1995,50(2):137-143
A heat-stable enzyme was isolated from the cellulase complex of a thermophilic strain of the micromyceteThielavia terrestris. The purified enzyme exhibited both endoglucanase and xylanase activities and had a mol mass of 69,000 Daltons and an isoelectric
point of 6.4. When the cells were grown at 48°C, the initial activity of the purified enzyme using carboxymethylcellulose
as a substrate was 150 nkat/mg and the Michaelis constant was 6.6 g/L. The heat stability of the enzyme was high, losing only
20% of the initial activity after a 6-h incubation at 65 °C. When cultures were grown on microcrystalline cellulose and xylose
was added after 48 h of growth, endoglucanase and xylanase activities were more than doubled. Similar increases in these activities
were observed by growing the cultures on straw. 相似文献
195.
We describe an efficient synthesis of thia analogues of the vitamin D side chain that is based on the in situ generation of a thiolate anion and its alkylation with electrophiles. 相似文献
196.
B. A. Howell J. J. Powers D. B. Priddy 《Journal of Thermal Analysis and Calorimetry》2006,85(1):141-143
Light transmittance was
measured during heating of thin NaPO3 glass plates
at different heating rates. According to the results, the crystallization
of orthorhombic textured NaPO3 glass proceeds from
sample surfaces into their interior due to the foregoing surface nucleation.
The glass surface crystallization process resulted in the sigmoidal decrease
of the optical transmittance. Elaborated data lead to the activation energy
of glass surface crystallization of the value of 182.8 kJ mol -1. 相似文献
197.
Pavel . Volkov Nina I. Ivanova Nina K. Gusarova Boris G. Sukhov Kseniya O. Khrapova Lev E. Zelenkov Vladimir I. Smirnov Tatyana N. Borodina Tamara I. Vakul'skaya Spartak S. Khutsishvili Boris A. Trofimov 《Heteroatom Chemistry》2015,26(5):329-334
Secondary phosphine chalcogenides react with diacetone‐d‐glucose (DAG) in the system CCl4/Et3N (70°C, 4–24 h) to afford DAG chalcogenophosphinates in up to 79% yield, thus paving a short way to optically active chalcogenophosphinates with glucose moieties. As an example, a mild regioselective hydrolysis (70°C, aqueous MeCOOH) of DAG bis(2‐phenylethyl)selenophosphinate) obtained leads to monoacetone‐d‐glucose bis(2‐phenylethyl)selenophosphinate. 相似文献
198.
One‐Step Synthetic Access to Isosteric and Potent Anticancer Nitrogen Heterocycles with the Benzo[c]phenanthridine Scaffold 下载免费PDF全文
Tamara N. Steinhauer Dr. Ulrich Girreser Dr. Christopher Meier Prof. Dr. Mark Cushman Prof. Dr. Bernd Clement 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(24):8301-8308
A versatile one‐step two‐component cyclization to build new tetracyclic nitrogen heterocycles is described. Ortho‐methylhetarenecarbonitrile components were condensed with aldehydes to access a large library of differently substituted ring systems. The heterocyclic core can be easily modified by variation of the position of the endocyclic nitrogen atom in the o‐methylhetarenecarbonitrile substrate. The manner of the nucleophilic attack that leads to the condensation can be triggered by different electron‐density distribution in the molecule induced by the position of the nitrogen atom. Taking this into account, there is an electronic preference that leads to either pyridophenanthrolines or the corresponding pyridoazacarbazoles as the main products. We demonstrate the high antitumor potential of some of our synthesized heterocycles, which is strongly dependent on the substitution pattern introduced through the aldehyde component. The position and number of endocyclic nitrogen atoms play an important role regarding cytotoxicity of the studied compounds. 相似文献
199.
Probing the Limits of Selectivity in a Recognition‐Mediated Reaction Network Embedded within a Dynamic Covalent Library 下载免费PDF全文
Tamara Kosikova Harry Mackenzie Prof. Douglas Philp 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(5):1831-1839
Two recognition‐mediated reaction processes operating through reactive binary complexes drive resolution of a 24‐component dynamic covalent library, assembled from individual aldehydes and nucleophiles. The effectiveness of the library resolution and selective amplification of one recognition‐enabled species over another is limited by the difference in the rates of the recognition‐mediated reactive processes and the strength of the recognition processes employed in the dynamic system. 相似文献