Showing papers by "Jesús Jiménez-Barbero published in 2004"

Chemical biology of the sugar code.

Abstract: A high-density coding system is essential to allow cells to communicate efficiently and swiftly through complex surface interactions. All the structural requirements for forming a wide array of signals with a system of minimal size are met by oligomers of carbohydrates. These molecules surpass amino acids and nucleotides by far in information-storing capacity and serve as ligands in biorecognition processes for the transfer of information. The results of work aiming to reveal the intricate ways in which oligosaccharide determinants of cellular glycoconjugates interact with tissue lectins and thereby trigger multifarious cellular responses (e.g. in adhesion or growth regulation) are teaching amazing lessons about the range of finely tuned activities involved. The ability of enzymes to generate an enormous diversity of biochemical signals is matched by receptor proteins (lectins), which are equally elaborate. The multiformity of lectins ensures accurate signal decoding and transmission. The exquisite refinement of both sides of the protein-carbohydrate recognition system turns the structural complexity of glycans--a demanding but essentially mastered problem for analytical chemistry--into a biochemical virtue. The emerging medical importance of protein-carbohydrate recognition, for example in combating infection and the spread of tumors or in targeting drugs, also explains why this interaction system is no longer below industrial radarscopes. Our review sketches the concept of the sugar code, with a solid description of the historical background. We also place emphasis on a distinctive feature of the code, that is, the potential of a carbohydrate ligand to adopt various defined shapes, each with its own particular ligand properties (differential conformer selection). Proper consideration of the structure and shape of the ligand enables us to envision the chemical design of potent binding partners for a target (in lectin-mediated drug delivery) or ways to block lectins of medical importance (in infection, tumor spread, or inflammation).

The first synthesis of substituted azepanes mimicking monosaccharides: a new class of potent glycosidase inhibitors.

Abstract: The synthesis of the first examples of seven-membered ring iminoalditols, molecules displaying an extra hydroxymethyl substituent on their seven-membered ring compared to the previously reported polyhydroxylated azepanes, has been achieved from D-arabinose in 10 steps using RCM of a protected N-allyl-aminohexenitol as a key step. While the (2R,3R,4R)-2-hydroxymethyl-3,4-dihydroxy-azepane 10, a seven-membered ring analogue of fagomine, is a weak inhibitor of glycosidases, the (2R,3R,4R,5S,6S)-2-hydroxymethyl-3,4,5,6-tetrahydroxy-azepane 9 selectively inhibits green coffee bean α-galactosidase in the low micromolar range (Ki = 2.2 µM) despite a D-gluco relative configuration.

Diffusion ordered spectroscopy as a complement to size exclusion chromatography in oligosaccharide analysis

Abstract: A series of N-acetyl-chitooligosaccharides (GlcNAc)1‐6 have been studied by a nuclear magnetic resonance (NMR) method, diffusion ordered spectroscopy (DOSY). DOSY has also been applied to two additional synthetic related oligosaccharides [GlcNH2-(GlcNAc)4 and GlcNH2-(GlcNAc)2GlcNAcSO3Na]. A plot of the log of the determined diffusion coefficients (logD) of (GlcNAc)n versus the log of molecular weight was linear (6 points, R 2 a 0.995). The molecular weights of the two synthetic chitin derivatives could be estimated to within 10% error. The processed NMR data of all the chitooligosaccharides was also plotted in a polyacrylamide gel‐like format to aid visual interpretation. Moreover, the logD value of the NMR signal resonances of a chitinbinding protein (hevein) changed as a function of a given titrated ligand, (GlcNAc)6. Evidence for a 2:1 hevein:(GlcNAc)6 complex is detected by DOSY at high hevein:(GlcNAc)6 ratios. This data is consistent with published analytical ultracentrifugation and isothermal titration calorimetry data. A 1:1 complex is preferred at higher ligand concentrations. DOSY can complement size exclusion chromatography in carbohydrate research with the advantage that oligosaccharides are more readily detected by NMR.

Intramolecular carbohydrate-aromatic interactions and intermolecular van der Waals interactions enhance the molecular recognition ability of GM1 glycomimetics for cholera toxin.

Abstract: The design and synthesis of two GM1 glycomimetics, 6 and 7, and analysis of their conformation in the free state and when complexed to cholera toxin is described. These compounds, which include an (R)-cyclbhex-yllactic acid and an (R)-phenyllactic acid fragment, respectively, display significant affinity for cholera toxin. A detailed NMR spectroscopy study of the toxin/glycomimetic complexes, assisted by molecular modeling techniques, has allowed their interactions with the toxin to be explained at the atomic level. It is shown that intramolecular van der Waals and CH-n carbohydrate-aromatic interactions define the conformational properties of 7, which adopts a three-dimensional structure significantly preorganized for proper interaction with the toxin. The exploitation of this kind of sugar-aromatic interaction, which is very well described in the context of carbohydrate/protein complexes, may open new avenues for the rational design of sugar mimics.

NMR and Modeling Studies of Protein–Carbohydrate Interactions: Synthesis, Three‐Dimensional Structure, and Recognition Properties of a Minimum Hevein Domain with Binding Affinity for Chitooligosaccharides

Abstract: HEV32, a 32-residue, truncated hevein lacking eleven C-terminal amino acids, was synthesized by solid-phase methodology and correctly folded with three cysteine bridge pairs. The affinities of HEV32 for small chitin fragments—in the forms of N,N′,N′′-triacetylchitotriose ((GlcNAc)3) (millimolar) and N,N′,N′′,N′′′,N′′′′,N′′′′′-hexaacetylchitohexaose ((GlcNAc)6) (micromolar)—as measured by NMR and fluorescence methods, are comparable with those of native hevein. The HEV32 ligand-binding process is enthalpy driven, while entropy opposes binding. The NMR structure of ligand-bound HEV32 in aqueous solution was determined to be highly similar to the NMR structure of ligand-bound hevein. Solvated molecular-dynamics simulations were performed in order to monitor the changes in side-chain conformation of the binding site of HEV32 and hevein upon interaction with ligands. The calculations suggest that the Trp21 side-chain orientation of HEV32 in the free form differs from that in the bound state; this agrees with fluorescence and thermodynamic data. HEV32 provides a simple molecular model for studying protein–carbohydrate interactions and for understanding the physiological relevance of small native hevein domains lacking C-terminal residues.

Hydrogen‐Bonding Cooperativity: Using an Intramolecular Hydrogen Bond To Design a Carbohydrate Derivative with a Cooperative Hydrogen‐Bond Donor Centre

Abstract: 12 paginas, 8 figuras, 2 esquemas, 3 tablas.-- Supporting information for this article is available on the WWW under http://www.chemeurj.org/ or from the author.

Enzymatic synthesis of complex glycosaminotrioses and study of their molecular recognition by hevein domains.

Abstract: Hevein, a protein found in Hevea brasiliensis, has a CRD domain, which is known to bind chitin and GlcNAc-containing oligosaccharides. By using NMR and molecular modeling as major tools we have demonstrated that trisaccharides containing GalNAc and ManNAc residues are also recognized by hevein domains. Thus far unknown trisaccharides GlcNAcβ(1→4)GlcNAcβ(1→4)ManNAc (1) and GalNAcβ(1→4)GlcNAcβ(1→4)ManNAc (2) were synthesized with the use of β-N-acetylhexosaminidase from Aspergillus oryzae. This method is based on the rather unique phenomenon that some fungal β-N-acetylhexosaminidases cannot hydrolyze disaccharide GlcNAcβ(1→4)ManNAc (5) contrary to chitobiose GlcNAcβ(1→4)GlcNAc (4) that is cleaved and, therefore, cannot be used as an acceptor for further transglycosylation. Both trisaccharides 1 and 2 were prepared by transglycosylation from disaccharidic acceptor 5 in good yields ranging from 35% to 40%. Our observations strongly indicate that the present nature of the modifications of chitotriose (GlcNAcβ(1→4)GlcNAcβ(1→4)GlcNAc, 3) at either the non-reducing end (GalNAc instead of GlcNAc) or at the reducing end (ManNAc instead of GlcNAc) do not modify the mode of binding of the trisaccharide to hevein. The association constant values indicate that chitotriose (3) binding is better than that of 1 and 2, and that the binding of 1 (with ManNAc at the reducing end) is favored with respect to that of 2 (with ManNAc at the reducing end with a non-reducing GalNAc moiety).

Polyhydroxyazepanes mimicking monosaccharides: Synthesis of an α-D-galacto-like iminoheptitol

Abstract: The synthesis of three new examples of seven-membered ring iminoalditols, displaying an extra hydroxymethyl group on the ring compared to the previously reported polyhydroxylated azepanes, has been achieved from D-lyxonolactone. None of them, including the alpha-D-galacto-like azepane (7), showed significant glycosidase inhibition on green coffee bean alpha-galactosidase and other commercially available hydrolases.

The First Synthesis of Substituted Azepanes Mimicking Monosaccharides: A New Class of Potent Glycosidase Inhibitors.

Abstract: The synthesis of the first examples of seven-membered ring iminoalditols, molecules displaying an extra hydroxymethyl substituent on their seven-membered ring compared to the previously reported polyhydroxylated azepanes, has been achieved from D-arabinose in 10 steps using RCM of a protected N-allyl-aminohexenitol as a key step. While the (2R,3R,4R)-2-hydroxymethyl-3,4-dihydroxy-azepane 10, a seven-membered ring analogue of fagomine, is a weak inhibitor of glycosidases, the (2R,3R,4R,5S,6S)-2-hydroxymethyl-3,4,5,6-tetrahydroxy-azepane 9 selectively inhibits green coffee bean α-galactosidase in the low micromolar range (Ki = 2.2 µM) despite a D-gluco relative configuration.