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471.
Amit Dubey Braja Gopal Mishra Divya Sachdev M. Sowmiya 《Reaction Kinetics and Catalysis Letters》2008,93(1):149-155
Aluminated mesoporous silica (Al-SBA-15) with different amounts of Al contents were synthesized and used for the synthesis
of 3,4-dihydropyrimidine-2(1H)-ones in the liquid phase, as well as under microwave conditions. The catalytic activity results
showed very high conversion and yields of the products over many substituted aromatic aldehydes. 相似文献
472.
473.
An efficient high yielding improved method for the enantio- and diastereoselective cyclopropanation of chiral epoxides using triethylphosphonoacetate and base (Wadsworth-Emmons cyclopropanation) is reported. The utility of this protocol is illustrated by concise and practical synthesis of cascarillic acid, grenadamide and L-(-)-CCG-II, a cyclopropane containing natural products. 相似文献
474.
A Ajay S Sharma MP Gupt V Bajpai Hamidullah B Kumar MP Kaushik R Konwar RS Ampapathi RP Tripathi 《Organic letters》2012,14(17):4306-4309
A new approach to synthesize a homologous series of 14-, 15-, and 16-membered drug-like, macrocyclic glycoconjugates involving TBAHS promoted azide-propenone intramolecular cycloaddition in designed C-glycopyranosyl butenones from a simple sugar d-glucose and d-mannose is reported. 相似文献
475.
Sharma S Dubey NK Dasgupta AK Sahu M Benjamin B Mullangi R Srinivas NR 《Biomedical chromatography : BMC》2012,26(2):232-238
A highly sensitive, rapid assay method has been developed and validated for the estimation of JI-101 in human plasma and urine using LC-MS/MS-ESI in the positive-ion mode. The assay procedure involves extraction of JI-101 and alfuzosin (internal standard, IS) from human plasma/urine with a solid-phase extraction process. Chromatographic resolution was achieved on two Zorbax SB-C(18) columns connected in series with a PEEK coupler using an isocratic mobile phase comprising acetonitrile-0.1% formic acid in water (70:30, v/v). The total run time was 2.0 min. The MS/MS ion transitions monitored were 466.20 → 265.10 for JI-101 and 390.40 → 156.10 for IS. The method was subjected to rigorous validation procedures to cover the following: selectivity, sensitivity, matrix effect, recovery, precision, accuracy, stability and dilution effect. In both matrices the lower limit of quantitation was 10.0 ng/mL and the linearity range extended from ~10.0 to 1508 ng/mL in plasma or urine. The intra- and inter-day precisions were in the ranges 1.57-14.5 and 6.02-12.4% in plasma and 0.97-15.7 and 8.66-10.2% in urine. This method has been successfully applied for the characterization of JI-101 pharmacokinetics in cancer patients. 相似文献
476.
A coupling of novel liquid–liquid–solid microextraction (LLSME) technique based on porous hydrophobic membrane and Fourier-transform infrared spectroscopy has been presented for the detection, identification and quantification of markers and simulants of nerve agents. Two isomers O,O′-dihexyl methylphosphonate (DHMP) and O,O′-dipentyl isopropylphosphonate (DPIPP) were chosen as model analytes for the study. In the present technique, organic phase was immobilised within the pores of membrane after fixing it in an assembly, which was then immersed into aqueous sample of target analytes for extraction. The analytes were directly determined on the surface of membrane by FTIR spectroscopy without elution. On comparison with solid phase microextraction (SPME), LLSME was found to be much more efficient. The method was optimised and quantitative analyses were performed using calibration curves obtained via Beer's law and employing processing of spectra obtained, via a multivariate calibration technique partial least square (PLS). Relative standard deviations (RSDs) for intraday repeatability and interday reproducibility were found to be in the range of 0.20–0.50% and 0.20–0.60%, respectively. Limit of detection (LOD) was achieved up to 15 ng mL−1. Applicability of the method was tested with an unknown real sample obtained in an international official proficiency test (OPT). 相似文献
477.
478.
Kanaujia PK Tak V Pardasani D Gupta AK Jain R Dubey DK 《European journal of mass spectrometry (Chichester, England)》2006,12(4):261-269
This communication describes GC-MS analysis of bis(trimethylsilyl) (bis-TMS) derivatives of bis(2-hydroxyethylthio)alkanes (BHETAs) and bis(2-hydroxyethylsulfonyl) alkanes (BHESAs) which are important markers of sulfur mustard class of chemical warfare agents. The study was undertaken with a view to develop spectral database of these compounds for verification analysis of Chemical Weapons Convention (CWC). Based on the obtained mass spectra of bis-TMS derivatives of BHETAs and BHESAs, the fragmentation routes are proposed, which explain most of the characteristic ions. 相似文献
479.
It is known that in the three-dimensional structure of a protein, certain amino acids can interact with each other in order to provide structural integrity or aid in its catalytic function. If these positions are mutated the loss of this interaction usually leads to a non-functional protein. Directed evolution experiments, which probe the sequence space of a protein through mutations in search for an improved variant, frequently result in such inactive sequences. In this work, we address the use of machine learning algorithms, Boolean learning and support vector machines (SVMs), to find such pairs of amino acid positions. The recombination method of imparting mutations was simulated to create in silico sequences that were used as training data for the algorithms. The two algorithms were combined together to develop an approach that weighs the structural risk as well as the empirical risk to solve the problem. This strategy was adapted to a multi-round framework of experiments where the data generated in the present round is used to design experiments for the next round to improve the generated library, as well as the estimation of the interacting positions. It is observed that this strategy can greatly improve the number of functional variants that are generated as well as the average number of mutations that can be made in the library. 相似文献
480.
Pardasani D Palit M Gupta AK Kanaujia PK Sekhar K Dubey DK 《Journal of chromatography. A》2006,1108(2):166-175
Detection and identification of environmental signatures of chemical warfare agents is an important aspect of verification program of Chemical Weapons Convention (CWC). Alkylphosphonic acids (APAs) are ultimate and persistent degradation products of nerve agents. Their identification in a sample submitted for off-site analysis infers possible indication of contamination with nerve agents. This paper describes the development of a new sample preparation method which involves 'in situ derivatization and extraction' (INDEX) of acids from water. Derivatization is performed by alkylation of APAs with alkylbromides in surfactant less microemulsion (SLME). The derivatized analytes were analyzed by gas chromatography coupled with mass spectrometry. The developed method involves simultaneous derivatization (alkylation) and extraction of acidic analytes mediated by surfactant less microemulsion. Various derivatization-extraction parameters such as solvent, reaction time and temperature, base and alkyl bromides were optimized. Pentyl bromide in the presence of potassium carbonate and diisopropylamine at 100 degrees C derivatized the selected acids efficiently. Kinetic data for alkylation of methylphosphonic acids and some carboxylic acids were obtained to assess their relative susceptibility for alkylation in microemulsion. Methylphosphonic acid and isopropyl methylphosphonic acid took 140-150 min to reach completion while carboxylic acids took 100 min to complete the reaction. INDEX could be successfully performed even in the presence of interfering Ca(2+) and Mg(2+) ions. 相似文献