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Group Migration (group + migration)
Selected AbstractsFormation of Indene Derivatives from Bis(cyclopentadienyl)titanacyclopentadienes with Alkyl Group Migration via Carbon,Carbon Bond Cleavage.CHEMINFORM, Issue 17 2006Tamotsu Takahashi Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Catalytic Hydrogenation of Cyanohydrin Esters as a Novel Approach to N -Acylated ,-Amino Alcohols , Reaction Optimisation by a Design of Experiment ApproachEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 7 2006Lars Veum Abstract The catalytic hydrogenation of acylated cyanohydrins and subsequent intramolecular migration of the acyl group to yield pharmaceutically interesting N -acyl ,-amino alcohols is shown to be a successful one-pot preparation method. The combination of a multistep DoE approach and high-throughput methodology proved to be an effective strategy for the optimisation of the reaction. With the favoured catalyst/solvent combination of nickel on alumina in dioxane, both hydrogenation and acyl group migration proceeded smoothly, giving the N -acyl ,-amino alcohols in yields (determined by GC) of up to 90,% for aliphatic substrates and up to 50,% for benzylic ones, the latter being more prone to side reactions. No racemisation was found to occur at the chiral centre of an aliphatic molecule when an enantiopure cyanohydrin ester was used, though a minor decrease in ee was observed with a benzylic substrate. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Chemical synthesis and biotinylation of the thrombospondin domain TSR2PROTEIN SCIENCE, Issue 5 2009Theresa K. Tiefenbrunn Abstract The type 1 repeat domain from thrombospondin has potent antiangiogenic activity and a structurally interesting fold, making it an attractive target for protein engineering. Chemical synthesis is an attractive approach for studying protein domains because it enables the use of unnatural amino acids for site-specific labeling and detailed structure-function analysis. Here, we demonstrate the first total chemical synthesis of the thrombospondin type 1 repeat domain by native chemical ligation. In addition to the natural domain, five sites for side chain modification were evaluated and two were found to be compatible with oxidative folding. Several challenges were encountered during peptide synthesis due to the functional complexity of the domain. These challenges were overcome by the use of new solid supports, scavengers, and the testing of multiple ligation sites. We also describe an unusual sequence-specific protecting group migration observed during cleavage resulting in +90 Da and +194 Da adducts. Synthetic access to this domain enables the synthesis of a number of variants that can be used to further our understanding of the biochemical interaction network of thrombospondin and provide insight into the structure and function of this important antitumorogenic protein domain. [source] Theoretical study of protonated xylenes: ethene elimination and H,C-scrambling reactionsJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 11 2004Bjørnar Arstad Abstract Quantum chemical calculations have been carried out to investigate various unimolecular rearrangements that can take place in protonated gas-phase xylenes. Hydrogen and methyl group ring migrations were investigated. The barriers for hydrogen migrations are lower than the barriers for methyl group migrations. Mechanisms for ring expansion to seven-membered rings, and for contraction to five-membered rings were studied. Both of these mechanisms can eventually lead to ethene elimination. The most favourable ring expansion step goes through a 1,3-hydrogen shift from a methyl group onto the arenium ring, forming a protonated methylcycloheptatriene. Interconversions between various ring-expanded forms have been investigated. Re-contraction can lead to an ethylbenzenium ion that could subsequently split off ethene. Alternatively, the xylenium ion can contract to a five-membered ring. The immediate product is a bicyclic ion (bicyclo[3.1.0]hexane skeleton) that can rearrange further to give an ethylbenzenium ion, or the five-ring system can split off ethene, and be converted into a cyclopentadienyl ion that can isomerize into a benzenium ion. Stable structures and transition states are calculated both at the B3LYP/cc-pVTZ//B3LYP/6-311G(d,p) and at the MP2/cc-pVTZ//MP2/6-31G(d) levels. The energies needed for ring expansion or ring contraction are not very different, and the calculations suggest that both reaction paths are possible, but the energy needed for actually splitting off an ethene molecule is lower along the expansion path. Copyright © 2004 John Wiley & Sons, Ltd. [source] | ||||||||||