Search results for "Cyclic compound"
showing 10 items of 819 documents
Characterization of a Double Metal Cyanide (DMC)-Type Catalyst in the Polyoxypropylation Process: Effects of Catalyst Concentration
2014
The alkaline catalysts commonly applied to alkoxylation are characterized by a limited spectrum of activity caused by an irreversible termination of the polyether chains. The presented results show that double metal cyanide (DMC) catalysts reduce or eliminate the aforementioned adverse rearrangement of hydroxyl groups. Moreover, DMC catalysts indicate high activity at low concentrations (ppm range), as expressed by high polymerization rates. It was demonstrated that decreased concentrations of DMC catalyst irreversibly influence its reactivity and the dispersity of the obtained products, as exemplified by the production and determination of selected polyoxypropylenediols at different concen…
Water compatible gold(III)-catalysed synthesis of unsymmetrical ethers from alcohols.
2008
An efficient and broad-scoped method for the preparation of unsymmetrical ethers from alcohols catalysed by the simplest and least expensive gold catalyst, NaAuCl 4 , is described for the first time. The procedure enables the etherification of benzylic and tertiary alcohols with moderate to good yields under mild conditions with low catalyst loading. Symmetrical ethers, the usual side products in the etherification of alcohols, were not detected in this case. The formation of the racemic ether from a chiral benzyl alcohol suggests the intermediacy of a carbocation, which has not previously been postulated for gold-catalysed reactions involving alcohols.
Total oxidation of naphthalene using bulk manganese oxide catalysts
2013
Several Mn2O3 catalysts have been synthesized using different preparation methods and tested for the total oxidation of naphthalene, a model polycyclic aromatic compound. The catalysts have been characterized by several physico-chemical techniques such as XRD, TPR, XPS, EDX and TEM. The surface area of the catalyst seems to be of paramount importance, since the mass normalized activity of catalysts increases as the surface area of the Mn2O3 catalysts increases. Consequently, a high surface area ordered mesoporous Mn2O3 catalyst, obtained through a nanocasting route using mesoporous KIT-6 silica as a hard template, was the most efficient catalyst for the deep oxidation of naphthalene. In add…
Synthese mehrerer polymerhomologer reihen von diol-oligo-urethanen. Synthese von makromolekeln einheitlicher größe. V. Mitt.
1961
Mit Hilfe des Duplikationsverfahrens und durch schrittweise Synthese werden mehrere polymerhomologe Reihen von Diol-oligo-urethanen synthetisiert. Die Anwendbarkeit dieser Methode wird eingehend diskutiert. Die Diol-oligo-urethane werden durch Endgruppenanalyse charakterisiert. Several homologous polymeric series of diol-oligo-urethanes are prepared by the method of duplication and by synthesis step by step. The application of these methods is discussed thoroughly. The diol-oligo-urethanes are characterized by end-group analysis.
Fluorination of some highly functionalized cycloalkanes: chemoselectivity and substrate dependence.
2017
A study exploring the chemical behavior of some dihydroxylated β-amino ester stereo- and regioisomers, derived from unsaturated cyclic β-amino acids is described. The nucleophilic fluorinations involving hydroxy–fluorine exchange of some highly functionalized alicyclic diol derivatives have been carried out in view of selective fluorination, investigating substrate dependence, neighboring group assistance and chemodifferentiation.
Synthetic Approaches to the Lamellarins—A Comprehensive Review
2014
The present review discusses the known synthetic routes to the lamellarin alkaloids published until 2014. It begins with syntheses of the structurally simpler type-II lamellarins and then focuses on the larger class of the 5,6-saturated and -unsaturated type-I lamellarins. The syntheses are grouped by the strategy employed for the assembly of the central pyrrole ring.
Synthetic approaches towards huperzine A and B
2013
Huperzine A and B are potent acetylcholinesterase inhibitors and promising against Alzheimer's disease. Completed and formal total syntheses of these medically relevant alkaloids are presented and discussed.
Human DNA Telomeres in Presence of Oxidative Lesions: The Crucial Role of Electrostatic Interactions on the Stability of Guanine Quadruplexes
2019
By using all atom molecular dynamics simulations, we studied the behavior of human DNA telomere sequences in guanine quadruplex (G4) conformation and in the presence of oxidative lesions, namely abasic sites. In particular, we evidenced that while removing one guanine base induces a significant alteration and destabilization of the involved leaflet, human telomere oligomers tend, in most cases, to maintain at least a partial quadruplex structure, eventually by replacing the empty site with undamaged guanines of different leaflets. This study shows that (i) the disruption of the quadruplex leaflets induces the release of at least one of the potassium cations embedded in the quadruplex channe…
Synergistic cytotoxic interactions between sodium butyrate, MG132 and camptothecin in human retinoblastoma Y79 cells.
2000
This paper studies the effects caused in human retinoblastoma Y79 cells by treatment with combinations of sodium butyrate, the inhibitor of topoisomerase I camptothecin and the inhibitor of 26S proteasome MG132. The combination of sodium butyrate and camptothecin resulted in a strong synergistic cytotoxicity, as revealed by combination indices of 0.77 and 0.52 calculated at IC(50) and IC(75). Synergistic interactions were also demonstrated for combinations of sodium butyrate and MG132, camptothecin and MG132 and for a combination of all three compounds. The cytotoxic effects observed after the combined treatments can be considered a consequence of apoptosis, as suggested by the appearance o…
Anti-Inflammatory Activity of Flavonol Glycosides fromErythrospermum monticolumDepending on Single or Repeated Local TPA Administration
1995
Two anti-inflammatory principles were isolated from the methanol extract of the leaves of Erythrospermum monticolum (Flacourtiaceae). The isolation was based on a guided bioassay of the inhibitory activity on TPA-induced ear edema in mice. These compounds were identified as quercetin 3-O-xylosyl(1-->2) rhamnoside and quercetin 3-O-rhamnoside. In addition, their effects on a chronic topic inflammation model were evaluated.