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Reaction Outcome (reaction + outcome)

Distribution by Scientific Domains

Chemistry	75%

Selected Abstracts

Epoxidation of Polyunsaturated Fatty Acid Double Bonds by Dioxirane Reagent: Regioselectivity and Lipid Supramolecular Organization

HELVETICA CHIMICA ACTA, Issue 10 2006
Stanislav
Abstract The use of dimethyldioxirane (DMD) as the epoxidizing agent for polyunsaturated fatty acids was investigated. With fatty acid methyl esters, this is a convenient method for avoiding acidic conditions, using different solvents, and simplifying the isolation procedures, with less contamination due to by-products. The reagent was also tested with free fatty acids in water. In this case, the supramolecular organization of fatty acids influenced the reaction outcome, and the epoxidation showed interesting regioselective features. The CC bonds closest to the aqueous-micelle interface is the most favored for the interaction with dimethyldioxirane. The preferential epoxidation of linoleic acid (=,(9Z,12Z)-octadeca-9,12-dienoic acid) to the 9,10-monoepoxy derivative was achieved, with a high yield and 65% regioselectivity. In case of arachidonic acid (=,(5Z,8Z,11Z,14Z)-eicosa-5,8,11,14-tetraenoic acid) micelles, the regioselective outcome with formation of the four possible monoepoxy isomers was studied under different conditions. It resulted to be a convenient synthesis of ,cis -5,6-epoxyeicosatrienoic acid' (=,3-[(2Z,5Z,8Z)-tetradeca-2,5,8-trienyl]oxiran-2-butanoic acid), whereas in reverse micelles, epoxidation mostly gave ,cis -14,15-epoxyeicosatrienoic acid (=,(5Z,8Z,11Z)-13-(3-pentyloxiran-2-yl)trideca-5,8,11-trienoic acid). [source]

DNA gyrase requirements distinguish the alternate pathways of Mu transposition

MOLECULAR MICROBIOLOGY, Issue 2 2003
Tanya D. Sokolsky
Summary The MuA transposase mediates transposition of bacteriophage Mu through two distinct mechanisms. The first integration event following infection occurs through a non-replicative mechanism. In contrast, during lytic growth, multiple rounds of replicative transposition amplify the phage genome. We have examined the influence of gyrase and DNA supercoiling on these two transposition pathways using both a gyrase-inhibiting drug and several distinct gyrase mutants. These experiments reveal that gyrase activity is not essential for integration; both lysogens and recombination intermediates are detected when gyrase is inhibited during Mu infection. In contrast, gyrase inhibition causes severe defects in replicative transposition. In two of the mutants, as well as in drug-treated cells, replicative transposition is almost completely blocked. Experiments probing for formation of MuA,DNA complexes in vivo reveal that this block occurs very early, during assembly of the transposase complex required for the catalytic steps of recombination. The findings establish that DNA structure-based signals are used differently for integrative and replicative transposition. We propose that transposase assembly, the committed step for recombination, has evolved to depend on different DNA /architectural signals to control the reaction outcome during these two distinct phases of the phage life cycle. [source]

Tin-Free Radical Alkoxyamine Addition and Isomerization Reactions by Using the Persistent Radical Effect: Variation of the Alkoxyamine Structure

CHEMISTRY - A EUROPEAN JOURNAL, Issue 8 2005
Kian Molawi Dipl.-Chem.
Abstract Various C-centered radicals can efficiently be generated through thermal CO-bond homolysis of alkoxyamines. This method is used to perform environmentally benign radical cyclization and intermolecular addition reactions. These alkoxyamine isomerizations and intermolecular carboaminoxylations are mediated by the persistent radical effect (PRE). In the paper, the effect of the variation of the alkoxyamine structure,in particular steric effects in the nitroxide moiety,on the outcome of the PRE mediated radical reactions will be discussed. Fourteen different nitroxides were used in the studies. It will be shown that reaction times can be shortened about 100 times upon careful tuning of the alkoxyamine structure. Activation energies for the CO-bond homolysis of the various alkoxyamines are provided. The kinetic data are used to explain the reaction outcome of the PRE-mediated processes. [source]

Investigations on the Iron-Catalyzed Asymmetric Sulfide Oxidation

CHEMISTRY - A EUROPEAN JOURNAL, Issue 4 2005
Julien Legros Dr.
Abstract The development of an enantioselective sulfide oxidation involving a chiral iron catalyst and aqueous hydrogen peroxide as oxidant is described. In the presence of a simple carboxylic acid, or a carboxylate salt, the reaction affords sulfoxides with remarkable enantioselectivities (up to 96,% ee) in moderate to good yields. The influence of the structure of the additive on the reaction outcome is reported. In the sulfoxide-to-sulfone oxidation a kinetic resolution (with s=4.8) occurs, which, however, plays only a negligible role in the overall enantioselective process. Furthermore, a positive nonlinear relationship between the ee of the product and that of the catalyst has been found. On the basis of these observations, a possible catalyst structure is proposed. [source]