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1.
Saadi Bayat Emilia Abd Malek Normi M. Yahaya Abu Bakar Salleh Bimo Ario Tejo Mohd Basyaruddin Abdul Rahman 《Tetrahedron letters》2014
The promiscuous aldo–ketoreductase (AKR) enzyme is used as a sustainable biocatalyst for the first time to catalyze asymmetric aldol reactions in aqueous medium. The reactions between aromatic aldehydes and cyclic/acyclic ketones give the corresponding products in moderate yields and enantioselectivities in the presence of water. The influence of solvents, the mole ratio of substrates, and enzyme concentration are investigated. The mechanism of the AKR1A1-catalyzed aldol reaction is also discussed. 相似文献
2.
Michael addition reactions of aldehyde to β-nitrostyrene catalyzed by L-proline were investigated by using controlled, monomode microwave-assisted technique in a closed vessel system. Ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim]NTf2) was used as the reaction medium to replace the commonly used volatile organic solvents and as a good absorbing solvent during Michael reaction under the influence of microwave irradiation. The Michael product is clean and generates good yields in short reaction times with moderate results on enantioselectivity (ee). In this work, optimization of proline-catalyzed Michael reaction was carried out using response surface methodology (RSM) based on a three-factor-three-level central composite design (CCD). Various reaction parameters including catalyst loading (5–30 mol%), reaction time (5–40 min), and substrate (2–5 equivalent ratio) were investigated. A high Michael yield (96.5%) with 36.9 ee% was obtained at the optimum conditions of 10.0 mol% catalyst loading, 5.0 min reaction time, and 2.0 substrate equivalent ratio.
[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.] 相似文献
3.
A method for the amidation of aldehydes with PhI=NTs/PhI=NNs as the nitrogen source and an inexpensive iron(II) chloride + pyridine as the in situ formed precatalyst under mild conditions at room temperature or microwave assisted conditions is described. The reaction was operationally straightforward and accomplished in moderate to excellent product yields (20-99%) and with complete chemoselectivity with the new C-N bond forming only at the formylic C-H bond in substrates containing other reactive functional groups. By utilizing microwave irradiation, comparable product yields and short reaction times of 1 h could be accomplished. The mechanism is suggested to involve insertion of a putative iron-nitrene/imido group to the formylic C-H bond of the substrate via a H-atom abstraction/radical rebound pathway mediated by the precatalyst [Fe(py)(4)Cl(2)] generated in situ from reaction of FeCl(2) with pyridine. 相似文献
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5.
I. Ario 《Meccanica》2014,49(8):1967-1983
We review a multiple Duffing oscillation, based on static bifurcation theory. We find that it is useful to consider the structural instability of a folding truss with possible imperfections as a theoretical model for a Duffing problem with multiple potential wells. Theoretical bifurcation analysis revealed that the equilibrium path on this model has a “hilltop bifurcation.” In addition, we have considered the elastic (in-)stability of several folding models with imperfections. The present model is very sensitive near a critical point, leading to strong geometrical nonlinearity. We found that there are both global and local dynamic behaviours that are related to bifurcation and imperfect influences, which correspond to the structure of the multiple homo- and heteroclinic orbits. We suggest a theoretical model for hilltop bifurcation, based on the static bifurcation problem and perturbation theory, to assist in the identification of the structural mechanisms of the global and local dynamics of different paths. Such models are very useful for investigating the essential and invariant nonlinear phenomena of the extended Duffing oscillator model. 相似文献
6.
Background
The first aim of the work was to analyze in detail the complexity of the aggregates formed upon overexpression of recombinant proteins in E. coli. A sucrose step gradient succeeded in separating aggregate subclasses of a GFP-GST fusion protein with specific biochemical and biophysical features, providing a novel approach for studying recombinant protein aggregates. 相似文献7.
Rahman RN Tejo BA Basri M Rahman MB Khan F Zain SM Siahaan TJ Salleh AB 《Applied biochemistry and biotechnology》2004,118(1-3):11-20
Candida rugosa lipase was modified via reductive alkylation to increase its hydrophobicity to work better in organic solvents. The free
amino group of lysines was alkylated using propionaldehyde with different degrees of modification obtained (49 and 86%). Far-ultraviolet
circular dichroism (CD) spectroscopy of the lipase in aqueous solvent showed that such chemical modifications at the enzyme
surface caused a loss in secondary and tertiary structure that is attributed to the enzyme unfolding. Using molecular modeling,
we propose that in an aqueous environment the loss in protein structure of the modified lipase is owing to disruption of stabilizing
salt bridges, particularly of surface lysines. Indeed, molecular modeling and simulation of a salt bridge formed by Lys-75
to Asp-79, in a nonpolar environment, suggests the adoption of a more flexible alkylated lysine that may explain higher lipase
activity in organic solvents on alkylation. 相似文献
8.
A method to prepare α-acyl-β-amino acid and 2,2-diacyl aziridine derivatives efficiently from Cu(OTf)(2) + 1,10-phenanthroline (1,10-phen)-catalyzed amination and aziridination of 2-alkyl substituted 1,3-dicarbonyl compounds with PhI═NTs is described. By taking advantage of the orthogonal modes of reactivity of the substrate through slight modification of the reaction conditions, a divergence in product selectivity was observed. In the presence of 1.2 equiv of the iminoiodane, amination of the allylic C-H bond of the enolic form of the substrate, formed in situ through coordination to the Lewis acidic metal catalyst, was found to selectively occur and give the β-aminated adduct. On the other hand, increasing the amount of the nitrogen source from 1.2 to 2-3 equiv was discovered to result in preferential formal aziridination of the C-C bond of the 2-alkyl substituent of the starting material and formation of the aziridine product. 相似文献
9.
Alkyl Ethers as Traceless Hydride Donors in Brønsted Acid Catalyzed Intramolecular Hydrogen Atom Transfer 下载免费PDF全文
Dhika Aditya Gandamana Dr. Bin Wang Dr. Ciputra Tejo Dr. Benoit Bolte Prof. Fabien Gagosz Prof. Shunsuke Chiba 《Angewandte Chemie (International ed. in English)》2018,57(21):6181-6185
A new protocol for the deoxygenation of alcohols and the hydrogenation of alkenes under Brønsted acid catalysis has been developed. The method is based on the use of either a benzyl or isopropyl ether as a traceless hydrogen‐atom donor, and involves an intramolecular hydride transfer as a key step, which is achieved in a regio‐ and stereoselective manner. 相似文献
10.
Saadi Bayat Emilia Abdulmalek Bimo Ario Tejo Abu Bakar Salleh Yahaya M. Normi 《合成通讯》2013,43(23):3130-3140
In this work, three forms of a novel octapeptide have been evaluated as asymmetric catalysts for the Michael reaction. Low quantity catalyst loading, ecofriendly solvents, and reusability of organocatalyst successfully applied to attain excellent yields and moderate enantioselectivities in the Michael reaction. [Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resources: Full experimental and spectral details.] 相似文献