共查询到20条相似文献,搜索用时 15 毫秒
1.
Svetlana V. ShishkinaAndriy Tarnovskiy Vladimir RozhkovOleg V. Shishkin Oleg LukinAlexander Shivanyuk 《Tetrahedron》2012,68(46):9429-9434
In the crystalline state two molecules of resorcin[4]arene tetrabenzoates and four chloride anions form molecular wraps containing two Et3NH+ cations. The structure and composition of the wraps depend on the length of the alkyl chains at the narrow rim of the macrocycle. Resorcin[4]arene tetrabenzoates interact with ammonium salts in CDCl3. 相似文献
2.
3.
Rongwei Teng Chingseng AngDavid McManus David ArmstrongShaiolim Mau Antony Bacic 《Tetrahedron letters》2003,44(30):5661-5664
Ginsenosides from Panax species were acylated regioselectively by Novozyme 435 with vinyl acetate as the acetyl donor in organic solvents to afford mono-acyl ginsenosides. 相似文献
4.
Monoacylated derivatives of a complete set of 2,3- and 3,4-vicinal diols of steroids were prepared by regioselective lipase-catalysed transesterification reactions. The enzymes displayed different selectivities towards the vicinal diols depending on the configuration of the hydroxyl groups. 相似文献
5.
<正>A series of monosubstituted troxerutin esters have been synthesized by enzyme-catalyzed regioselective acylation of troxerutin in nonaqueous medium.Using divinyl dicarboxylates(CH_2=CH-OOC-(CH_2)_n-COO-CH=CH_2,n = 2,3,4,7,8,11) featuring different chain length as acyl donors and alkaline protease from Bacillus subtilis as catalyst,troxerutin was regioselective acylated at B' ethoxyl group.The results indicated that the regioselectivity of the enzyme-catalyzed acylation was not affected by the chain length of the acyl donor. 相似文献
6.
Zhi Wang Yuxin Zhang Lu Zheng Xiuyun Cui He Huang Xin Geng 《Green Chemistry Letters and Reviews》2018,11(3):312-317
The enzymatic regioselective acylation of resveratrol was achieved in organic solvents catalyzed by the lipase from Candida sp. 99–125 (CSL) under microwave irradiation. Influences of various reaction conditions have been studied. After selecting the optimum conditions [MTBE (20?ml, aw?=?0.38), resveratrol (0.1?mmol), vinyl acetate (1.0?mmol) and CSL (100.0?mg) under microwave irradiation (35°C, 400 W)], CSL exhibited a satisfied enzyme activity (281?±?11?μmol/g/h) and yield of 75% for 4′-O-acetyl- resveratrol could be obtained in about 4?h when performing the reaction on a 25-fold-larger scale.Schematic illustration of the enzymatic regioselective acylation of resveratrol catalyzed by the lipase from Candida sp. 99–125 (CSL) under microwave irradiation. 相似文献
7.
Selective lipase-catalyzed acylation of 41-desmethoxyrapamycin has been achieved with a quaternary carboxylic acid avoiding the use of vinyl ester activation. Among the acyl donors investigated, the novel butanedione-monooxime and the N-acetylhydroxamate ester proved to be the most efficient donors, comparable in reactivity to the undesired vinyl ester and allowing selective, preparative acylation on gram scale in excellent yields. These new donors are proposed as sustainable and process-friendly alternatives to the widely used vinyl ester substrate activation in lipase-catalyzed acylations of secondary alcohols. 相似文献
8.
Enzymatic catalysis has become a common tool in both academia and industrial chemistry. The efforts of chemists over recent decades have led to the rationalization of the mechanism of action of biocatalysts, which have been routinely incorporated into many synthetic sequences. Nowadays, a further step consists in expanding the application of enzymes to the modification of complex molecular scaffolds common to many pharmaceutical leads isolated from nature. Regioselective enzymatic acylation is a process which has been profitably applied for this purpose in recent times, leading to new drugs with improved activity, stability and pharmacokinetic properties. This tutorial review provides an overview of this subject employing two classes of enzymes, hydrolases and acyltransferases, in the recently concluded decade although some representative older studies are commented upon, if required. We shall place special emphasis on those examples in which the novel acylated derivatives have improved the activity or properties of the parental molecules. 相似文献
9.
Werner A. P. Luck 《Angewandte Chemie (International ed. in English)》1980,19(1):28-41
The orientation defect model can be used for quantitative estimates and for understanding the properties of H-bonded liquids, such as water and alcohol. The defect concentrations can be determined by vibrational spectroscopy, and the applicability of the approximation procedure derives from considering H-bonds as chemical equilibria. Possible extensions of the simple model are critically discussed. 相似文献
10.
The MNDO method has been modified for the calculation of the properties of complexes with hydrogen bonds S-H-X, X = N, O, F, S. The results obtained are in good agreement with the experimental data. 相似文献
11.
Theoretical insights into the mechanism of acetylcholinesterase-catalyzed acylation of acetylcholine
Acylation of acetylcholine (ACh) catalyzed by acetylcholinesterase (AChE) has been studied using high-level theoretical calculations on a model system that mimics the reaction center of the enzyme, and compared with uncatalyzed acylation reaction. The geometries of all the intermediates and transition states, activation energies, and solvent effects have been calculated. The calculations predict simultaneous formation of two short-strong hydrogen bonds (SSHB) in the rate-determining transition state structures [the first SSHB involves the hydrogen atom of Ser-200 (H(s)) and another involves the hydrogen atom of His-440 (H(h))]. In the intermediate states, the H-bond corresponding to H(h) involves SSHB, whereas the one corresponding to H(s) does not. 相似文献
12.
C. Sndorfy 《Journal of Molecular Structure》2006,790(1-3):50-54
In moderately strong hydrogen bonds, hydrogen bond formation increases the anharmonicity constant of the high frequency stretching vibration, significantly but not dramatically. This increase tends to increase with the strength of the hydrogen bond. The main cause of the fine structure and breadth of this band is, however, coupling with both the low frequency stretching and bending vibrations of the bridge, despite the smallness of the coupling constants. Second–order perturbation theory is sufficient to interpret the observed frequencies in the case of moderately strong hydrogen bonds. HCNHF, O–H:O, O–H:N, and N–H:N hydrogen bonds are considered. 相似文献
13.
Tomohiro Sugahara Dr. Jing‐Dong Guo Prof. Dr. Takahiro Sasamori Prof. Dr. Shigeru Nagase Prof. Dr. Norihiro Tokitoh 《Angewandte Chemie (International ed. in English)》2018,57(13):3499-3503
The catalytic activation of small neutral molecules followed by the formation of C?C bonds is a highly important method to increase the complexity and/or value of simple starting materials. Reported is an isolable digermyne, a compound with a Ge≡Ge bond, which acts as a precatalyst for the cyclotrimerization of terminal arylacetylenes to afford the corresponding 1,2,4‐triarylbenzenes with absolute regioselectivity. The results demonstrate that bespoke main‐group‐element compounds can catalytically activate and transform small neutral organic molecules and induce the formation of C?C bonds. 相似文献
14.
The MNDO method has been modified to calculate the properties of the structures involving hydrogen bonds X···H—Y, X, Y = N, O and F. A new method (referred to as MNDO/H) has been tested by calculation of a wide range of molecular systems with weak and strong (ionic) hydrogen bonds. The results obtained are in good agreement with the experimental data. In the cases where direct comparisons are possible, the MNDO/H method seems to give more accurate values of hydrogen bond energy than the ab initio method using STO-4-31G basis set. 相似文献
15.
Francisco M. Muñiz 《Tetrahedron letters》2008,49(5):790-793
The proximity of the 4,5-diamino groups in a 9,9′-dimethylxanthene skeleton provides unique reactivity due to aggregation effects. While treatment with 1 equiv of an isocyanate yields the diurea and starting material, under similar conditions, Boc2O provides essentially only the monocarbamoyl derivative. 相似文献
16.
Simon G. Rachor Dr. Robert Müller Prof. Dr. Martin Kaupp Prof. Dr. Thomas Braun 《欧洲无机化学杂志》2023,26(2):e202200668
The hydrogen bonding in the Au(I) complex [Au(F ⋅ HF)(SPhos)] (SPhos=dicyclohexyl(2’,6’-dimethoxy[1,1’-biphenyl]-2-yl)phosphane) ( 1 a ⋅ HF) has been analysed by IR and NMR measurements, revealing the formation of an unsymmetrical bifluoride moiety. The data are in excellent agreement with DFT calculations. Comparisons to analogous complexes bearing NHC (NHC=N-heterocyclic carbene) ligands demonstrated a comparable bonding situation. The identity of the halogen bond in the compound [Au(F ⋅ IC6F5)(SPhos)] ( 1 a ⋅ IC6F5) in CD2Cl2 has been estimated, and van't Hoff data for the equilibrium between [Au(F)(SPhos)] ( 1 a ) and IC6F5 with [Au(F ⋅ IC6F5)(SPhos)] are ΔH0=−8.1(3) kJ mol−1 and ΔS0=−36(1) J (mol K)−1. The latter are also in agreement with DFT calculations. For all calculations, comparisons between an explicit and implicit solvent model were drawn. Single crystal X-ray diffraction studies were performed for [Au(F ⋅ 2IC6F5)(BrettPhos)] ⋅ 2IC6F5 (BrettPhos=2-(dicyclohexylphosphino)-3,6-dimethoxy-2’,4’,6’-triisopropyl-1,1’-biphenyl) ( 1 b ⋅ 4IC6F5) demonstrating the presence of halogen bonds to Au(I) fluorido complexes in the solid state. 相似文献
17.
Pseudomonas fluorescens lipase (Amano) was found to be highly regioselective (85%) in the catalysed transesterification of 1,6-anhydro-β-D-glucopyranose using vinyl acetate as an acyl donor and solvent. 相似文献
18.
19.
Carlos A.D. SousaFabio Rizzo-Aguiar M. Luísa C. ValeXerardo García-Mera Olga CaamañoJosé E. Rodríguez-Borges 《Tetrahedron letters》2012,53(9):1029-1032
A route to selective functionalization of polyhydroxypyrrolidines is described. The method is based on orthogonal protection/deprotection along the process of synthesis of the referred pyrrolidines, which consist in hydroxylation of the double bond of 2-azabicyclo[2.2.1]hept-5-enes followed by its oxidative cleavage and in situ reduction of the intermediate dialdehyde. The synthesis of a novel N-hydroxypyrrolidine is also described. 相似文献
20.
AbstractBenzyl imidazole was successfully lithiated using n-BuLi at ?78?°C and verified by deuterium incorporation. The chemical reaction of the lithiated benzimidazole was explored with a series of different electrophiles. This approach was utilized to synthesize new anti and syn diphenyl organocatalysts for trans-diol functionalization. 相似文献