Search results for "Esters"
showing 10 items of 305 documents
Enantiodifferentiation of N-benzyloxycarbonylaminophosphonic and phosphinic acids and their esters using cyclodextrins by means of capillary electrop…
2005
Capillary electrophoresis was successfully applied for separation of the enantiomers of N-benzyloxycarbonyl-alpha-aminophosphonic and alpha-aminophosphinic acids as well as their ethyl and phenyl monoesters with the use of a range of commercially available cyclodextrins (alpha, beta and hydroxypropyl-gamma-cyclodextrins) as chiral selectors. The dependence of effectiveness of separation on type and concentration of these chiral selectors as well as on pH of background electrolyte was examined in some detail.
Synthesis of fluorescent (benzyloxycarbonylamino)(aryl)methylphosphonates
2014
The synthesis of a library of structurally variable aromatic esters of (benzyloxycarbonylamino)(aryl)methylphosphonic acids is described by means of the Oleksyszyn reaction. The library was enlarged by the application of a Suzuki–Miayra approach and by preparation of mixed esters.
Photo-Oxidative and Soil Burial Degradation of Irrigation Tubes Based on Biodegradable Polymer Blends
2019
: Irrigation tubes based on biodegradable polymers were prepared via an extrusion-drawing process by Irritec and compared to conventional pipes made of high-density polyethylene (HDPE). A commercial polylactide/poly (butyleneadipate-co-butyleneterephthalate) (PLA/PBAT) blend (Bio-Flex®
Novel concepts on the recovery of by-products from alkaline pulping
2016
Innovative biorefinery concepts were developed for the separation and utilization of organic materials, especially aliphatic carboxylic acids, lignin, and extractives, which are formed as by-products during wood-based alkaline delignification processes. The partial recovery of sodium as NaOH and aliphatic carboxylic acids from hardwood soda-AQ black liquor was studied via electrodialysis. The lignin was partly (about 59 % of the initial lignin) precipitated from black liquor by carbonation (pH to about 8.5) followed by electrodialysis or H2SO4 (pH to about 2), with subsequent precipitation of more lignin and the liberation of aliphatic acids. The Na2SO4 formed was successfully separated fro…
First Highly Diastereoselective Synthesis of syn α-Methyl β-Fluoroalkyl β-Amino Esters
1999
A new two-step approach for the diastereoselective synthesis of the syn α-methyl β-fluoroalkyl β-amino esters 4 has been developed. This approach is based on the chemical reduction of the fluorinated β-enamino esters 3, which have been previously obtained from imidoyl chlorides 1 and lithium ester enolates, with ZnI2/NaBH4 as the reducing agent. The process takes place with high syn diastereoselectivity and good to excellent yields. A metal-chelated six-membered model has been suggested to explain the stereochemical outcome of the reduction reaction.
Synthesis of conformationally restricted 1,2,3-triazole-substituted ethyl β- and γ-aminocyclopentanecarboxylate stereoisomers. Multifunctionalized al…
2010
Abstract Stereoisomers of 1,2,3-triazole-functionalized, conformationally restricted β- or γ-amino esters with a cyclopentane skeleton were efficiently synthetized from the bicyclic β-lactam 6-azabicyclo[3.2.0]hept-3-en-7-one (1) and Vince γ-lactam (15) in five or six steps involving the azide–alkyne 1,3-dipolar cycloaddition of azido-substituted amino ester stereoisomers with nonsymmetric acetylenes. The azide–alkyne click reactions were investigated under thermal and Cu(I)-catalyzed conditions. Surprisingly, the thermally induced cycloaddition furnished the corresponding 1,4-triazoles regioselectively, which also took place selectively in response to Cu(I) catalysis.
The Structure and Metabolism of Carbohydrates
1994
Compared with the variety of carbohydrates in plants, relatively few sugars or sugar derivatives are regularly found in animals either free or as components of more complex compounds. However, it is possible that sugars originating from plants in the diet are transiently retained in animals and distort the normal sugar spectrum. Approximately a dozen sugars and sugar derivatives are regularly found in animals: the pentoses d-ribose and 2-deoxy-d-ribose; the hexoses d-glucose, d-galactose, d-mannose, d-fructose and l-fucose; the uronic acids d-glucuronic acid and l-iduronic acid; and the hexosamines d-glucosamine and d-galactosamine. In addition, d-erythrose, d-ribulose, d-xylulose and d-sed…
Selective Transformation of Norbornadiene into Functionalized Azaheterocycles and β‐Amino Esters with Stereo‐ and Regiocontrol
2021
Novel functionalized azaheterocycles with multiple chiral centers have been accessed from readily available norbornene β-amino acids or β-lactams across a stereocontrolled synthetic route, based on ring-opening metathesis (ROM) of the staring unsaturated bicyclic amino esters, followed by selective cyclization through ring-closing metathesis (RCM). The RCM transformations have been studied under various experimental conditions to assess the scope of conversion, catalyst, yield, and substrate influence. The structure of the starting norbornene β-amino acids predetermined the structure of the new azaheterocycles, and the developed synthetic route took place with the conservation of the config…
Differential reactivity of fluorinated homopropargylic amino esters vs gold(I) salts. The role of the nitrogen protecting group
2015
The reaction of several homopropargyl amino esters 4, bearing aromatic substituents and a benzyl group as nitrogen substituents, with gold(I) salts gave rise to fluorinated quinolines 6 in a tandem hydroarylation-isomerization process. On the other hand, homopropargyl amino esters 7 containing a carbamate group underwent the carbonyl addition over the triple bond in the presence of gold(I) salts, rendering fluorinated oxazines 8. The use of chiral sulfoxides allowed us to develop the asymmetric version of this protocol. This two processes complete the differential reactivity showed by these types of susbtrates, depending on the nature of the nitrogen protecting group. (C) 2014 Elsevier B.V.…
Isolierung und Charakterisierung einer Acetylester-Hydrolase aus Aspergillus rtiger / Isolation and Characterization of an Acetylester-Hydrolase from…
1980
Abstract The characteristic features of an acetic acid esters hydrolyzing enzyme (acetylesterase, EC 3.1.1.16) are described. The pH- and temperature optimum were 7.0 and 40 °C respectively. The stability of the enzyme regarding different pH- and temperature conditions was investigated. The molecular weight of the acetylesterase could be determined to 160000. A small acetic ester hydrolyzing activity was found too with a molecular weight of about 25000. The activity was not inhibited by addition of di-isopropylphosphorofluoridate (DFP) or physostigmine. The KM-value for glyceryl triacetate was about 90 mM. Concentration of the enzyme was done by ultrafiltration and column-chromatography. Th…