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Sugar Backbone (sugar + backbone)
Selected AbstractsSynthesis, Structure and Magnetic Properties of a Tetranuclear Copper(II) Complex on the Basis of a 2-Substituted Glucopyranoside Schiff Base Ligand,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2006Anja Burkhardt Abstract Condensation of a derivatized 2-aminoglucose fragment with salicylaldehyde affords the new sugar-based Schiff base ligand benzyl 4,6- O -benzylidene-2-deoxy-2-salicylideneamino-,- D -glucopyranoside (H2L). The reaction of the dibasic ligand H2L with [Cu(CH3COO)2]·H2O leads to the formation of the tetranuclear copper(II) complex [{Cu(L)}4] (3) by a self-assembly process. The X-ray structural analysis of complex 3 which crystallizes together with two molecules of chloroform and one molecule of ethanol in the space group P212121 revealed for all copper atoms a NO3 coordination environment with a square-planar geometry. The tetranuclear molecule 3 consists of four chiral building blocks {Cu(L)} with the rare 2,3-coordination of the trans -configured donor atoms of the sugar backbone. The observed coordination mode of the building blocks exemplifies how chitosan-derived polysaccharide ligands can act as a chiral support for transition-metal complexes. The C-3 alcoholate oxygen atoms of the carbohydrate unit is bridging adjacent {Cu(L)} moieties resulting in an eight-membered Cu4O4 ring with a boat-like conformation. Temperature-dependent magnetic measurements of 3 indicate moderate antiferromagnetic interactions between the four copper(II) ions with a coupling constant of J = ,130 cm,1.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Biophysical characterization of the interaction of high-density lipoprotein (HDL) with endotoxinsFEBS JOURNAL, Issue 23 2002Klaus Brandenburg The interaction of bacterial endotoxins [lipopolysaccharide (LPS) and the ,endotoxic principle' lipid A], with high-density lipoprotein (HDL) from serum was investigated with a variety of physical techniques and biological assays. HDL exhibited an increase in the gel to liquid crystalline phase transition temperature Tc and a rigidification of the acyl chains of the endotoxins as measured by Fourier-transform infrared spectroscopy and differential scanning calorimetry. The functional groups of the endotoxins interacting with HDL are the phosphates and the diglucosamine backbone. The finding of phosphates as target groups is in accordance to measurements of the electrophoretic mobility showing that the zeta potential decreases from ,50 to ,60 mV to ,20 mV at binding saturation. The importance of the sugar backbone as further target structure is in accordance with the remaining negative potential and competition experiments with polymyxin B (PMB) and phase transition data of the system PMB/dephosphorylated LPS. Furthermore, endotoxin binding to HDL influences the secondary structure of the latter manifesting in a change from a mixed ,-helical/,-sheet structure to a predominantly ,-helical structure. The aggregate structure of the lipid A moiety of the endotoxins as determined by small-angle X-ray scattering shows a change of a unilamellar/inverted cubic into a multilamellar structure in the presence of HDL. Fluorescence resonance energy transfer data indicate an intercalation of pure HDL, and of [LPS],[HDL] complexes into phospholipid liposomes. Furthermore, HDL may enhance the lipopolysaccharide-binding protein-induced intercalation of LPS into phospholipid liposomes. Parallel to these observations, the LPS-induced cytokine production of human mononuclear cells and the reactivity in the Limulus test are strongly reduced by the addition of HDL. These data allow to develop a model of the [endotoxin]/[HDL] interaction. [source] Heparin and Heparan Sulfate BiosynthesisIUBMB LIFE, Issue 4 2002Kazuyuki Sugahara Abstract Heparan sulfate is one of the most informationally rich biopolymers in Nature. Its simple sugar backbone is variously modified to different degrees depending on the cellular conditions. Thus, it matures to have an enormously complicated structure, which most likely exhibits a considerable number of unique overlapping sequences with peculiar sulfation profiles. Such sequences are recognized by specific complementary proteins, which form a huge group of "heparin-binding proteins," and the sugar sequences in turn support unique functions of the respective proteins through specific interactions. The heparan sulfate sequences are not directly encoded by genes, but are created by elaborate biosynthetic mechanisms, which ensure the generation of these indispensable sequences. In heparan sulfate biosynthesis, the tetrasaccharide sequence (GlcA-Gal-Gal-Xyl-), designated the protein linkage region, is first assembled on a specific Ser residue at the glycosaminoglycan attachment site of a core protein. A heparan sulfate chain is then polymerized on this fragment by alternate additions of GlcNAc and GlcA through the actions of glycosyltransferases with overlapping specificities encoded by the tumor suppressor EXT family genes. Then follow various modifications by N -deacetylation and N -sulfation of glucosamine, C5-epimerization of GlcA and multiple O -sulfations of the component sugars. Recent studies have achieved purification of several, and molecular cloning of most, of the enzymes responsible for these reactions. Some of these enzymes are bifunctional. The availability of cDNA probes has facilitated elucidation of the crystal structures for two of the biosynthetic enzymes, demonstration of their intracellular location, and their occurrence in complexes to achieve rapid and efficient synthesis of complex sugar sequences. Genomic structure and transcript analysis have shown the existence of multiple isoforms for most of the sulfotransferases. Many aspects of the heparan sulfate biosynthetic scheme are shared by the structural analog heparin, which is synthesized in mast cells and some other mammalian cells and is several-fold higher degree of polymerization and more extensive modification than heparan sulfate. [source] Modular Furanoside Diphosphite Ligands for Pd-Catalyzed Asymmetric Allylic Substitution Reactions: Scope and LimitationsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2005Montserrat Diéguez Abstract We have synthesized a library of furanoside diphosphite ligands for the Pd-catalyzed allylic substitution reactions of acyclic and cyclic allylic esters. The library has been designed to rapidly screen the ligands to uncover their important structural features and to determine the scope of diphosphite ligands in these catalytic reactions. After the systematic variation of the sugar backbone, the substituent at C-5 and the phosphite moieties, the diphosphite ligand 4c was found to be optimal in the Pd-catalyzed asymmetric allylic substitution of hindered (S1) and unhindered (S2,S5) substrates, yielding high activities [TOFs up to >3000,mol×(mol×h),1] and enantioselectivities (ees up to 99%). In addition, the screening of the library enabled us to find other suitable ligands for hindered disubstituted linear substrate S1 (ligands 1b,d, g and 4b, d, g) and for unhindered cyclic substrates S3,S5 (ligands 6c and 7c). [source] | ||||||||||