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Chemistry75%

Selected Abstracts

Stereodefined Access to 3-Deoxy Sugars Through a Tandem Baylis,Hillman and Lewis Acid Catalyzed Reaction Sequence

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 5 2010
Palakodety Radha Krishna
Abstract An innovative synthetic protocol is reported for the ready access to 3-deoxy sugars in both D and L forms as exclusive products (des >95,%) in high yields through a stereodefined Lewis acid catalyzed reaction sequence of the sugar-derived Baylis,Hillman adducts. [source]

Platinum Nanoparticles Supported on Ionic Liquid-Modified Magnetic Nanoparticles: Selective Hydrogenation Catalysts

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2007
Raed Abu-Reziq
Abstract A method for supporting platinum nanoparticles on magnetite nanoparticles is described. The method requires modification of the surface of the magnetic nanoparticles with ionic liquid groups. Before modification, the magnetic nanoparticles are not stable and easily aggregate and, after modification, the magnetite nanoparticles become highly stable and soluble in polar or non-polar organic solvents depending on the alkyl group of the linked ionic liquids. The supporting of platinum nanoparticles on the modified magnetic nanoparticles was achieved by adsorbing platinum salts (K2PtCl4) on the surface of the magnetite nanoparticles via ion exchange with the linked ionic liquid groups and then reducing them by hydrazine. The supported platinum nanoparticles were applied in the catalytic hydrogenation of alkynes in which cis -alkenes were selectively produced, and in the hydrogenation of ,,,-unsaturated aldehydes where the allyl alcohols were obtained as the exclusive products. The new catalyst can be easily separated from the reaction mixtures by applying an external magnetic field and recycled. [source]

Synthesis and Reactivity of 6,7-dihydrogeranylazides: Reagents for Primary Azide Incorporation into Peptides and Subsequent Staudinger Ligation

CHEMICAL BIOLOGY & DRUG DESIGN, Issue 2 2006
Juhua Xu
Protein farnesyltransferase (PFTase) catalyzes the attachment of a geranylazide moiety to a peptide substrate, N -dansyl-GCVIA. Because geranylazide is actually a mixture of isomeric, interconverting primary and secondary azides, incorporation of this isoprenoid into peptides can potentially result in a corresponding mixture of prenylated peptides. Here, we first examined the reactivity of geranyl azide in a model Staudinger reaction and determined that a mixture of products is formed. We then describe the synthesis of 6,7-dihydrogeranylazide diphosphate and demonstrate that this compound allows exclusive incorporation of a primary azide into a peptide. The resulting azide-containing peptide was derivatized with a triphenylphosphine-based reagent to generate an O -alkyl imidate-linked product. Finally, we show, using a series of model reactions, that the Staudinger ligation frequently produces small amounts of O -alkyl imidate products in addition to the major amide-linked products. Thus, the alkoxyimidates we have observed as the exclusive products in the reactions of peptides containing prenylated azides also appear to be a common type of product formed using other azide-containing reactants, although at greatly reduced levels. This method for chemical modification of the C-terminus of a protein should be useful for a variety of applications in protein chemistry. [source]

A Dynamic Tricopper Double Helicate

CHEMISTRY - A EUROPEAN JOURNAL, Issue 15 2006
Marie Hutin
Abstract The reaction between 8-aminoquinoline, 1,10-phenantholine-2,9-dicarbaldehyde, and copper(I) tetrafluoroborate gave a quantitative yield of a tricopper double helicate. The presence of dynamic covalent imine (CN) bonds allowed this assembly to participate in two reactions not previously known in helicate chemistry: 1) It could be prepared through subcomponent substitution from a dicopper double helicate that contained aniline residues. An electron-poor aniline was quantitatively displaced; a more electron-rich aniline competed effectively with the aminoquinoline, setting up an equilibrium between dicopper and tricopper helicates that could be displaced towards the tricopper through the addition of further copper(I). 2) Both dicopper and tricopper helicates could be prepared simultaneously from a mixture of phenanthroline dialdehyde, aniline, and aminoquinoline, which contained all possible imine condensation products in equilibrium. Following the addition of copper(I), thermodynamic equilibration on both covalent and coordinative levels eliminated all partially-formed and mixed imine ligands from the mixture, leaving the helicates as exclusive products. La réaction entre la 8-aminoquinoline, la 1,10-phenanthroline-2,9-dicarbaldehyde et le cuivre(i,) tetrafluoroborate conduit à la formation quantitative d'un double hélicate à trois cuivres. Grâce à la liaison imine (CN) dynamique et covalente, cet assemblage participe à deux réactions nouvelles dans la chimie des hélicates : 1) L'hélicate peut être préparé par la substitution de composants à partir d'un double hélicate à deux cuivres incorporant des anilines. Une aniline pauvre en électrons est déplacée quantitativement par l'aminoquinoline ; une aniline plus riche en électrons est déplacée plus difficilement, conduisant ainsi à un équilibre entre l'hélicate à deux cuivres et celui à trois cuivres. Cet équilibre peut être déplacé vers la formation de l'hélicate à trois cuivres par l'addition d'un excès de cuivre(i,). 2) Les hélicates à deux et trois cuivres peuvent être préparés simultanément en ajoutant du cuivre(i,) à un mélange d'aminoquinoline, d'aniline et de phenanthrolinecarbaldehyde contenant tous les produits de condensation possibles à l'équilibre. Suite à cet ajout, l'équilibre thermodynamique élimine les ligands partiellement formés ou mixtes, laissant les hélicates comme uniques produits. [source]