Showing papers on "Pyranose published in 1989"

Anomeric and Exo-Anomeric Effects in Carbohydrate Chemistry

Abstract: Publisher Summary This chapter discusses the several possibilities regarding the specification of the energy associated with the anomeric effect, and the experimental data concerning the configurational and conformational equilibria of the anomeric center and the related variations of valence geometry. The free-energy aspect of the anomeric effect as displayed by the equilibria of isomers is the area wherein the very concept was incepted and developed, and which still dominates its investigation. A considerable amount of data has been accumulated during the past two decades on the anomeric effect in terms of structure, energy, reactivity, and other properties. The description and understanding of the nature of stereoelectronic effects is an appropriate field for the application of organic quantum chemistry. Although several molecular orbital (MO) methods successfully describe the stereochemical behavior of pyranose models, their application to the more complex carbohydrates and oligosaccharides is limited at present due to economical reasons. The various rationalizations of the anomeric effect have been offered over the past years; they may be roughly divided into two main groups—namely, the electrostatic and the delocalization rationalization of the anomeric effect. It may be expected that the intramolecular interactions involved in the anomeric effect also influence the other points on the generalized reaction hypersurface.

The labellar sugar receptor ofDrosophila

Abstract: 1. The electrophysiology of the sugar receptor in labellar taste hairs ofDrosophila melanogaster (Diptera) was investigated using 33 monosaccharides, oligosaccharides, glucosides, and amino acids which in calyptrate flies are known to bind to specific receptor sites or which may be assigned to specific receptor sites on the basis of structural criteria. 2. The pyranose site ofDrosophila is very similar to the pyranose site of the calyptrate flies: regarding monosaccharides of the pyranose type three adjacent equatorial hydroxyl groups (C-2, C-3, C-4) seem to be important for stimulating effectiveness. On the other hand, it exhibits a more rigid stereospecificity with regard to the substituents at C-1 and C-5. 3. A furanose site as in calyptrate flies does not exist inDrosophila. First, D-galactose, phenylalanine and 2,5-anhydro-D-mannitol are not or nearly not stimulatory. Secondly, according to different sugar receptor responses after treatment of the taste hairs with papain, D-fucose binds to another receptor site than D-fructose. Thirdly, the effective conformation of D-fructose is not the furanose, but most probably the pyranose form as can be concluded from experiments with freshly prepared and equilibrium solutions of D-fructose. 4. The characteristic differences between the properties of the sugar receptors ofDrosophila and of the calyptrate flies lead to the suggestion that the actual number of types of receptor sites in the various fly species is greater than assumed up till now. The broad specificity of the sugar receptors of flies may therefore result from a mosaic of different types of highly specific receptor sites.

Isomeric equilibria of monosaccharides in solution. Influence of solvent and temperature

Abstract: The compositions of equilibrium mixtures of D-glucose, D-ribose, β-methyl glucopyranoside and β-methyl ribopyranoside in D2O and dimethyl sulphoxide-d6 have been determined by 1H nmr spectroscopy over the temperature range 0–90 °C in terms of the coexisting anomers, tautomers and conformers In glucose solutions only 4C1 pyranose forms could be detected, but the temperature dependence of the α/β ratio differs in the two solvents Ribose solutions consist of mixtures of six species, the relative concentrations of which display complex temperature dependences The experimental results are discussed in terms of solvation contributions to the relative free energies of the different species

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).

Scalar, dipolar-correlated and J-resolved 2D-NMR spectroscopy of the specific phenolic mycoside of Mycobacterium tuberculosis

Abstract: Two-dimensional chemical shift correlated (COSY), nuclear Overhauser (NOESY) and J-resolved spectroscopy were used to determine the complete structure of the major triglycosyl dimycocerosyl phenol phthiocerol of the tubercle bacillus (strain Canetti) without any other analytical technique. The COSY spectrum of the native glycolipid allowed the composition of the trisaccharide and the location of one methoxyl group to be determined through the assignment of the resonances of the non-anomeric methine protons. Information with respect to the configuration of the sugar residues, the pyranose structure and the linkage sites of the trisaccharide were obtained by the analysis of the COSY spectrum of the peracetylated glycolipid. The NOESY spectrum confirmed the linkage sites through the inter-residue connectivity across glycosidic linkages and allowed the determination of the sequence of the oligosaccharide and the configuration of its sugar residues from the through-space connectivities. The J-resolved spectroscopy was used to elucidate the structure of the glycolipid and gave additional data showing the presence of 11 non-equivalent methyl groups and allowing the recognition of two other analogues of the phenol phthiocerol derivative in the mixture. Thus, the non-destructive 2D-NMR spectroscopy was found to be satisfactory for the analysis of mycobacterial mycosides.

Monoclonal antibodies which recognise polysulphated polysaccharides

Abstract: The present invention relates to monoclonal antibodies which recognise polysulphated polysaccharides which contain 2,3-; 2,6-; or 4,6- disulphate ester pyranose ring substitution. These antibodies are used in assays for the detection and/or quantification of polysulphated polysaccharides which contain 2,3-; 2,6-; or 4,6- disulphate ester pyranose ring substitution in biological fluids. The invention also relates to diagnostic kits for use in the assays.

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.

Enzyme electrode for measuring malto-oligosaccharide and measuring apparatus using the same

Abstract: In an enzyme electrode for measuring malto-­oligosaccharides having an immobilized enzyme membrane containing glucoamylase and a glucose oxidizing enzyme such as glucose oxidase or pyranose oxidase, the glucoamylase and glucose or pyranose oxidizing enzyme are immobilized at a ratio Co of Co = Va Vo ≧ 0.4 where Va is the maximum reaction rate of glucoamylase as expressed in the glucose formation rate from maltose, and Vo is the maximum reaction rate of glucose or pyranose oxidizing enzyme as expressed in the hydrogen peroxide formation rate from glucose. In such enzyme electrode, malto-oligosaccharides are detected at the response value proportional to their degree of polymerization. Therefore, the malto-­oligosaccharides can be measured at the glucose converted concentration. This enzyme electrode can be use in an apparatus to measure simultaneously the concentrations of glucose and malto-­oligosaccharides.

Syntheses of Amino-dideoxyallose and Amino-deoxyribose Derivatives Using Acylnitroso Dienophiles.

Abstract: The dimethyl acetals 4 of (E)-2,4-pentadienal and of (E,E)- and (E,Z)-2,4-hexadienals undergo regio- and stereospecific cycloaddition reactions with in-situ-generated acylnitroso dienophiles 5a and 5b, leading thereby to the corresponding dihydrooxazines 7a–d and 8c–d. cis-Glycolization of these latter adducts stereospecifically gave the dihydro derivatives 9a–d and 10d which, after sequential hydrogenolysis, deacetalization, and instant cyclization, led to the aminodeoxyribose derivatives 17a, 17f, and 18, and to the amino-dideoxyallose compounds 17c and 17h. These piperidino-deoxysugar derivatives exhibit a strong anomeric effect, i.e. OHC(1) is always axial, which is explained in terms of a nN(π)-σ*(COH) orbital compression, as compared to the less pronounced one in the more classical pyranose series.