Showing papers on "Pyranose published in 1990"

Generation of α-D-glucopyranosylacetonitrilium ions. Concerning the reverse anomeric effect

Abstract: Reaction of the α- and β-anomers of the pent-4-enyl D-glucopyranoside (10) with N-bromosuccinimide in dry acetonitrile generated stereospecifically the α-D-glucopyranosylacetonitrilium ion (5α), which reacts in situ with 2-chlorobenzoic acid to afford the α-imide (8α). The result is in contrast to that predicted by the reverse anomeric effect and previous work on trapping carbohydrate acetonitrilium ions with 2-chlorobenzoic acid. The unusually large J12 7.3 Hz for 1-H of (8α) is rationalised by a substantial flattening of the pyranose ring at C-1 and C-2. Molecular dynamic studies on the model α-imide (12) support a flattened 4C1, conformation. Treatment of imide (8α) with sodium methoxide leads to the α-2-chlorobenzamide (9α), which was substantiated by independent synthesis of the β-2-chlorobenzamide (9β).

Significant conformational changes in an antigenic carbohydrate epitope upon binding to a monoclonal antibody

Abstract: Transferred nuclear Overhauser enhancement spectroscopy (TRNOE) was used to observe changes in a ligand's conformation upon binding to its specific antibody. The ligands studied were methyl O-beta-D-galactopyranosyl(1----6)-4-deoxy-4-fluoro-beta-D-galactopyra nos ide (me4FGal2) and its selectively deuteriated analogue, methyl O-beta-D-galactopyranosyl(1----6)-4-deoxy-2-deuterio-4-fluoro-beta -D- galactopyranoside (me4F2dGal2). The monoclonal antibody was mouse IgA X24. The solution conformation of the free ligand me4F2dGal2 was inferred from measurements of vicinal 1H-1H coupling constants, long-range 1H-13C coupling constants, and NOE cross-peak intensities. For free ligand, both galactosyl residues adopt a regular chair conformation, but the NMR spectra are incompatible with a single unique conformation of the glycosidic linkage. Analysis of 1H-1H and 1H-13C constants indicates that the major conformer has an extended conformation: phi = -120 degrees; psi = 180 degrees; and omega = 75 degrees. TRNOE measurements on me4FGal2 and me4F2dGal2 in the presence of the specific antibody indicate that the pyranose ring pucker of each galactose ring remains unchanged, but rotations about the glycosidic linkage occur upon binding to X24. Computer calculations indicate that there are two sets of torsion angles that satisfy the observed NMR constraints, namely, phi = -152 +/- 9 degrees; psi = -128 +/- 7 degrees; and omega = -158 +/- 6 degrees; and a conformer with phi = -53 +/- 6 degrees; psi = 154 +/- 10 degrees; and omega = -173 +/- 6 degrees. Neither conformation is similar to any of the observed conformations of the free disaccharide.(ABSTRACT TRUNCATED AT 250 WORDS)

Conformational aspects of oligosaccharides

Abstract: The three dimensional structure of oligosaccharides determines their interaction with receptors and hence is important for their biological activity. Conformational analysis of oligosaccharides makes the three dimensional structure available. The analysis of the conformation of oligosaccharides is usually determined by a combination of computational methods and experimental techniques. NMR spectroscopy is the most important experimental tool. The calculational techniques cover a wide range with most emphasis put into force field calculations. Conformational flexibility plays an important role in many though not in all oligosaccharide structures. Glycosidic linkages to a side chain of a pyranose ring are more flexible than are linkages to the pyranose ring. The major attempts are described to determine the three dimensional structure of oligosaccharides with the exception of homooligomers. This review covers conformational analyses of blood group antigens of N-linked and of O-linked oligosaccharide chains, of glycolipids, of oligosaccharides related to O-specific polysaccharides of bacteria, and of oligosaccharides related to proteoglycans.

Diels-Alder reactions of dieno-pyranosides. Anomeric versus allylic stereoselection

Abstract: A series of carbohydrate-derived dienes with different patterns of substitution on the pyranose ring were synthesized and their Diels-Alder reactions investigated. The diene moiety was incorporated into the pyranose ring by oxidation of 4-O-methanesulfonate esters of sugar derivatives to enals, followed by Witting alkenation. This new class of dienes underwent cycloaddition with maleimide or its N-phenyl derivative to give annulated pyranosides. The Diels-Alder reactions were highly stereoselective, giving single products in some cases. Structural analysis of the reaction products was carried out by NMR spectroscopy and X-ray crystallography. The results indicated a strong preference for the formation of the products resulting from addition of the dienophile to the face of the diene opposite the anomeric center. In cases where the anomeric and allylic substituents on the diene occupied opposite faces, addition of the dienophile occurred predominantly from the face opposite the more remote anomeric center

Assignment of anomeric configurations of pyranose sugars in oligosaccharides using a sensitive FAB-MS strategy

Abstract: This paper describes a sensitive strategy employing fast atom bombardment mass spectrometry (FAB-MS) for defining the anomeric configurations of pyranose sugars in oligosaccharides. The method, which is applicable to mixtures of reduced or unreduced oligosaccharides, is based upon FAB-MS analyses of deuteroacetylated derivatives before and after oxidation with chromium trioxide. This reagent, whose potential value in carbohydrate chemistry was first recognized by Angyal and which was subsequently more fully exploited by Lindberg, oxidizes beta-pyranosides to keto-esters leaving alpha-pyranosides largely intact. In this paper we show that the products of chromium trioxide oxidation can be successfully analysed at the microgram level using FAB-MS. The molecular and fragment ions produced in the FAB experiment define the number of sites oxidized and their location in the sequence. For samples which fragment poorly we describe a mild methanolysis procedure, compatible with FAB-MS, which preferentially cleaves the esters formed during the oxidation. Incorporation of an acetolysis step prior to oxidation permits analyses of polysaccharides. This oxidation/FAB-MS strategy should prove valuable in structural analyses of a wide range of biologically important carbohydrates which cannot be isolated in sufficient quantities to permit nuclear magnetic resonance studies.

π-Facial selectivity in Diels–Alder reactions of C-2-vinyl glycals. Stereocontrolled route to annulated C-glycopyranosides

Abstract: An allylic methoxy substituent at C-3 in C-2 vinyl glycals (1b,c) induces complete antiπ-facial selectivity in the thermal Diels–Alder reaction with malefic anhydride; in contrast, products resulting from anti and syn approaches are observed when linear acetylenic compounds are employed as dienophiles; the latter adducts readily aromatize to afford a mixture of products with the pyranose ring unchanged (8) and opened (9).

Crystal structure of diheterolevulosan II: α-d-Fructofuranose-β-d-fructopyranose 1,2′:2,1′ dianhydride and molecular mechanics calculations on diheterolevulosan II and IV with chair and boat conformations of the central 1,4-dioxane ring

Abstract: C12H20O10,M r=324.28, orthorhombic,P212121,a=9.4476(8),b=10.2247(8),c=13.5827(11) A,V=1312.07(18) A3,Z=4,D x=1.642 g cm−3, MoKα radiation (λ=0.71073 A)μ=1.4 cm−1,F(000)=688,T=295 K, finalR=0.041 for 1089 reflections withI≥2.5σa(I). The molecule consists of aβ-d-fructopyranose and a α-d-fructofuranose ring which are linked by a 1,4-dioxane ring. The pyranose ring and the dioxane ring both have a chair conformation, and the furanose ring has an envelope conformation. All six hydroxyl groups act as donors in intermolecular hydrogen bonding. Each molecule is hydrogen-bonded to eight neighbor molecules by fourteen hydrogen bonds, forming a three-dimensional framework. The hydrogen bonds of varying geometry give rise to five sharp hydroxyl stretch vibrations in the infrared spectrum. In diheterolevulosan IV the central dioxane ring is a boat. Molecular mechanics calculations on diheterolevulosan II and IV having different boat and chair conformations of the dioxane ring show that the lowest energy conformations correspond to the conformations observed in the crystal structure. For comparison the calculations also have been applied to 1,4-dioxane having boat and chair conformations.

Generation of α-D-Glucopyranosylacetonitrilium Ions. Concerning the Reverse Anomeric Effect.

Abstract: Reaction of the α- and β-anomers of the pent-4-enyl D-glucopyranoside (10) with N-bromosuccinimide in dry acetonitrile generated stereospecifically the α-D-glucopyranosylacetonitrilium ion (5α), which reacts in situ with 2-chlorobenzoic acid to afford the α-imide (8α). The result is in contrast to that predicted by the reverse anomeric effect and previous work on trapping carbohydrate acetonitrilium ions with 2-chlorobenzoic acid. The unusually large J12 7.3 Hz for 1-H of (8α) is rationalised by a substantial flattening of the pyranose ring at C-1 and C-2. Molecular dynamic studies on the model α-imide (12) support a flattened 4C1, conformation. Treatment of imide (8α) with sodium methoxide leads to the α-2-chlorobenzamide (9α), which was substantiated by independent synthesis of the β-2-chlorobenzamide (9β).

The Synthesis of Polyoxygenated Natural Products via Fully Synthetic Branched Pyranose Derivatives: Application to the Erythronolide Problem

Abstract: Reiterative cyclocondensation reactions and highly stereoselective functionalization reactions have been coordinated to reach a derivatized version (5b) of the seco acid of 6-deoxyerythronolide B (1). BACKGROUND In 1983 our laboratory began to explore some new possibilities for synthesizing extensively oxygenated natural products with a particular focus on polypropionates and polyols (ref. 1). The polypropionate pattern is readily identified in the backbone functionality of the macrolide aglycones (ref. 2). This pattern is also encountered, though in a less regular fashion, in various ionophores bearing pyranoid and furanoid substructures (ref. 3). The polyol functionality is widely encountered in carbohydrates. While the most common of the polyol arrangements are found in the pentoses and hexoses, we have been particularly concerned with the longer ensembles found in the complex higher order monosaccharides (ref. 4). The “carbohydrate-connection‘‘ in our synthesis of polypropionates is only slightly less obvious than is its involvement in our higher order monosaccharide efforts. Indeed, we treat the polypropionate targets in the context of more general issues in the synthesis of C-alkylated sugars. Our emphasis is on elaborating, by total synthesis, branched pyranose rings, For long chain polypropionate ensembles, the pyranose rings are disconnected at the 0-C1 (anomeric carbon) bond. An aldehyde function, fashioned from C I , becomes the device f o r chain elongation. In the case of the complex monosaccharides again an aldehyde is employed for major extension. In these cases the aldehyde projects from the pyranose or furanose matrix (either with or without an intervening spacer). The strategies for these two synthetic goals are summarized in Fig. 1. In this lecture we will describe our progress in using this type of generalized protocol toward the synthesis of 6-deoxyerythronolide B (1) (ref. 5 ) . As matters transpired, we focused on the tetra-protected seco ester 5b corresponding in its array of relative stereogenic centers to macrolide 1 . The identification of this particular compound as a target was not based on any prior knowledge that it would be an ideal or even workable substrate for lactonization (ref. 6). Our objective was to demonstrate the feasibility of our strategy for dealing with the eleven stereogenic centers contained in this macrolide system. Presumably the synthesis could be modified toward products with other protective arrangements which might be more suitable for macrolactonization. During our efforts it was found that the series of compounds 3-5 could be prepared from the natural product itself. Reduction of 6deoxyerythronolide B (1) with sodium borohydride in the presence of alumina afforded the crystalline dihydro compound 2.

Conformational features of idopyranose derivatives. The molecular structure of methyl 1,2,3,4-tetra-O-acetyl-α-L-idopyranuronate

Abstract: The molecular structure of the title compound has been determined by X-ray analysis. The structure was solved with the multisolution technique and the atomic parameters were refined by full-matrix least-squares refinement to an R value of 0.08 for 2 819 observed reflections. There are two molecules in the asymmetric unit. The bond lengths and bond angles of the pyranose rings are in good agreement within the limits of errors, except for the anomeric bond lengths. This is related to distinct conformations about the exocyclic anomeric bond which result in different respective orientations of the carbonyl O(62) and pyranic oxygen atoms. The conformation of each molecule is a normal 1C4(L) chair slightly deformed towards the 5Ho half chair. The molecular conformation of the title compound is compared to that of other idopyranose derivatives observed in the solid state.

Preparation of Glycosyl Halides Under Neutral Conditions.

Abstract: The anomeric hydroxyl group of various furanose and pyranose hemiacetals can be replaced by a fluorine, chlorine, bromine or iodine atom under neutral conditions using haloenamines.

Conformational Aspects of Oligosaccharides

Abstract: The three dimensional structure of oligosaccharides determines their interaction with receptors and hence is important for their biological activity. Conformational analysis of oligosaccharides makes the three dimensional structure available. The analysis of the conformation of oligosaccharides is usually determined by a combination of computational methods and experimental techniques. NMR spectroscopy is the most important experimental tool. The calculational techniques cover a wide range with most emphasis put into force field calculations. Conformational flexibility plays an important role in many though not in all oligosaccharide structures. Glycosidic linkages to a side chain of a pyranose ring are more flexible than are linkages to the pyranose ring. The major attempts are described to determine the three dimensional structure of oligosaccharides with the exception of homooligomers. This review covers conformational analyses of blood group antigens of N-linked and of O-linked oligosaccharide chains, of glycolipids, of oligosaccharides related to O-specific polysaccharides of bacteria, and of oligosaccharides related to proteoglycans.

Method of prohibiting glycolysis and production of glycolysis inhibitor

Abstract: PURPOSE:To enhance the accuracy of biochemical measurement by using the D-mannose which is decreased in the content of D-glucose by pyranose oxidizing enzyme, glucose dehydrogenase or glucokinase as the glycolysis inhibitor. CONSTITUTION:The D-mannose produced from coelococcus, amorphophallus powder, etc., is dissolved in a phosphoric acid soln. and the pyranose oxidizing enzyme is added thereto to effect reaction under stirring. The glucokinase and glucose-6-phosphoric acid dehydrogenase or the glucose dehydrogenase and mutarose may be used in place of the pyranose oxidizing enzyme. The D-glucose contained in the D-mannose is decomposed in this way and the incorporation of the D-glucose into sample blood is obviated when the D-mannose is added as the glycolysis inhibitor to the sample blood after a treatment.

Oxidative Hydrolysis of Conformationally Restrained Pent-4-enyl Glycosides: Formation of N-Acetyl-α-D-glucopyranosylamines.

Abstract: The α- and β-anomers of the conformationally restrained pent-4-enyl D-glucopyranosides (5) and (6) have been synthesised, and each anomer found to give stereospecifically the corresponding N-acetyl-α-D-glucopyranosylamines (7) and (8) as the major products on treatment with N-bromosuccinimide in 1% aqueous acetonitrile. In contrast, the strain free α- and β-anomers of pent-4-enyl 2,3,4,6-tetra-O-benzyl-D-glucopyranoside (10) yield only the corresponding pyranose (11). The α-configuration of the acetamide substituent in (7) and (8) was established by derivatisation of (8) to the 4,6-di-O-acetate (12α), subsequent 1H n.m.r. nuclear Overhauser enhancement (n.O.e.) experiments, and by independent synthesis of the 4,6-di-O-acetate-β-anomeric acetamide (12β).

13C NMR study of the distribution of the substituents in carboxymethyl ethers of polysaccharides

Abstract: 13C NMR in solution has been employed to make a comparative study of the distribution of the substituents in carboxymethyl ethers of amylose, dextran and cellulose. The resonance signals of the 13C nuclei in the spectra of the compounds studied is fully interpreted providing quantitative information on the position of the carboxymethyl groups in the D-glucopyranose unit of the macromolecules of the above mentioned polysaccharides. The reactivity of the OH groups in the reaction of carboxymethylation of amylose drops in the series C6>C2>C3 while for cellulose C>C6>C3 and for dextran C3>C2>C4. The influence of the structural factors on the difference in the reactivity of the OH group for certain positions of the carbon atoms of the pyranose cycle of the macromolecules of the polysaccharides of similar structure but differing in the details of the structure is discussed.