Glucopyranosyl Units Research Articles

Proton NMR spectroscopy assignment of d-glucose residues in highly acetylated starch

1H NMR spectroscopy assignments have been obtained for starch acetates using COSY and HOHAHA experiments by comparison with the spectra of amylose triacetate and of peracetylated malto-oligosaccharides (maltotriose, maltotetraose, maltoheptaose). These assignments are valuable for the location and evaluation of the substitution pattern in modified starches. The bulk of the 1H NMR spectra of highly acetylated starch strongly resembles the spectrum of amylose triacetate in which all protons are identified and display distinct chemical shifts. The resolving power of the HOHAHA experiment allowed the distinction of minor spin systems. Beside these strong signals pertaining to an average 2,3,6-tri- O-acetyl- α-(1 → 4) linked d-glucopyranose unit in an infinite chain, the combination of COSY and HOHAHA experiments allowed the identification of these systems to the terminal, n-1, n-2, and to partially acetylated glucopyranosyl units. As an example, two different preparations of starch acetates with degrees of substitution 2.74 and 2.63 were examined. In one case, NMR demonstrates that the defects of acetylation are random on the polymeric chain (with corresponding signals for unacylated secondary hydroxyl positions at δ 3.61 and 3.40) while in another case, these signals are not detectable, probably due to the presence of clusters of non-acetylated residue forming solid-like zones.

Characterisation of sorbed water molecules on neutral and ionic polysaccharides

Ionic and neutral polysaccharides with well-defined structures were chosen to investigate the mechanism of water sorption at different relative humidities. From an experimental point of view, the freezing water was determined by DSC when the total sorbed water was obtained from thermogravimetry. The isotherms of sorption and enthalpies of interaction were determined using the combination of a microbalance and a microcalorimeter. It is shown that freezing water appears for P/ P 0 > 0.85 especially with the neutral polymers. The differential molar enthalpy of interaction is higher for P/ P 0 < 0.85 corresponding to the fixation of two water molecules forming double H-bonds; this result is confirmed by molecular modelling; saturation is obtained experimentally for 4 water molecules interacting per glucose unit. On ionic polymers, the water retention increases especially over P/P 0 ∼ 0.8 and the enthalpy of interaction is higher for the first water molecules sorbed. For P/ P 0 ≅ 0.8, the numbers of bound water molecules found are 2 per glucopyranosyl unit for neutral polysaccharides, 5 for glucuronan and 9–10 for carboxymethylcellulose (CMC) of D S = 2 and hyaluronan (HA)

Synthesis of the methyl α-glycosides of some isomalto-oligosaccharides specifically deoxygenated at position C-3

Methyl α-isomaltoside and methyl α-isomaltotrioside specifically deoxygenated at position C-3 of various glucopyranosyl units were synthesized by condensation of either 1,6- di-O- acetyl-2,4-di-O- benzyl-3-deoxy-α,β- d -ribo- hexopyranose (7) or 1,6- di-O- acetyl-2,3,4-tri-O- benzyl-α,β- d-glucopyranose [mediated by silver perchlorate and tin(IV) chloride] with suitably blocked derivatives of methyl α- d-glucopyranoside, its 3-deoxy analog (6), or methyl 3′-deoxy α-isomaltoside (10), respectively.

Synthesis of the methyl α-glycosides of some isomalto-oligosaccharides specifically deoxygenated at position C-4

Methyl α-isomaltoside and methyl α-isomaltotrioside specifically deoxygenated at position C-4 of various glucopyranosyl units were synthesized by condensation of either 1,6-di- O-acetyl-2,3-di- O-benzyl-4-deoxy- α, β- d- xylo-hexopyranose (7) or 1,6-di- O-acetyl-2,3,4-tri- O-benzyl- α, β- d-glucopyranose (10) [mediated by silver perchlorate and tin(IV) chloride] with suitably blocked derivatives of methyl α-d-glucopyranoside, its 4-deoxy analog 6, or methyl 4′-deoxy α-isomaltoside (13), respectively.

Synthesis of methyl glycosides of some α-isomalto oligosaccharides specifically deoxygenated at position C-2

Methyl α-isomaltoside and methyl α-isomaltotrioside analogues specifically deoxygenated at position C-2 of various glucopyranosyl units were synthesized by condensation of either 6-O- acetyl-3-O- benzoyl-4-O- benzyl-1-O-tert- butyldimethylsilyl-2-deoxy-β- d-arabino- hexopyranose (trimethylsilyl triflate mediated) or 6-O- acetyl-2,3,4-tri-O- benzyl-α- d-glucopyranosyl chloride (mediated by silver carbonate and silver triflate) with suitably blocked derivatives of methyl α- d-glucopyranoside, its 2-deoxy analogue, or methyl 2′-deoxy-α-isomaltoside.

Isothiocyanates and cyclic thiocarbamates of α, α′-trehalose, sucrose, and cyclomaltooligosaccharides

6,6′-Dideoxy-6,6′-diisothiocyanato-α, α′-trehalose ( 4), 6-deoxy-6-isothiocyanato-α- d-fructofuranose β- d-fructopyranose 1,2′:2,1′-dianhydride ( 11), 6,6′-dideoxy-6,6′-diisothiocyanatosucrose ( 16), and per(6-deoxy-6-isothiocyanato)-cyclomaltohexaose ( 23), -cyclomaltoheptaose ( 27), and -cyclomaltooctaose ( 31) have been prepared in high yield by reaction of the corresponding amino sugars with thiophosgene. In the absence of base, all isothiocyanates were stable and could be stored and acetylated without decomposition. In the presence of triethylamine, 6,6′-dideoxy-6,6′-diisothiocyanato-α, α′-trehalose underwent intramolecular cyclisation involving HO-4 to give the corresponding bis(cyclic thiocarbamate). The product of cyclisation at a single glucopyranosyl unit was obtained in the treatment of the above diisothiocyanate with mixed (H +, HO −) ion-exchange resin. Under identical reaction conditions, 6,6′-dideoxy-6,6′-diisothiocyanatosucrose yielded exclusively the product of intramolecular cyclisation at the d-glucopyranosyl moiety, while derivatives of α- d-fructofuranose β- d-fructopyranose 1,2′:2,1′-dianhydride and cyclomaltooligosaccharides remained unchanged.

Molecular architecture of a galactoglucan from Rhizobium meliloti

Rhizobium meliloti mutants produce a linear, acidic exopolysaccharide with alternating galactopyranosyl and glucopyranosyl units having (1 → 3) linkages. It has a 4,6- O-pyruvic cyclic acetal group on the α-galactosyl and 6- O-acetyl ester group on the β-glucosyl units. X-ray diffraction patterns from polycrystalline and well oriented specimens of its potassium salt indicate that the polymer forms a 2-fold helix of pitch 15.89 Å. The three-dimensional structure has been determined and refined by using the X-ray intensities and the linked-atom least-squares technique. The details of the antiparallel packing arrangement of two helices in an orthorhombic unit cell, a = 14.49, b = 9.79, and c = 15.89 Å, reveal that each disaccharide repeating unit is associated with one potassium and three water molecules. The helices are interconnected by a series of ⋯ COO − ⋯ K + ⋯ W ⋯ COO − ⋯ interactions. Both pyruvyl and acetyl groups, which are on the periphery of the helix, are involved in the association of the polysaccharide chains and thus appear to be an integral component of the galactoglucan in the nodule invasion process.

Synthesis of methyl ?-isomalto-oligosaccharides specifically deoxygenated at position 2 of the terminal glycopyranosyl unit

Methyl α-isomaltoside and methyl α-isomaltotrioside specifically deoxygenated at position C-2 of the terminal glucopyranosyl unit were synthesized by trimethylsilyltriflate-mediated condensation of 3,4,6-tri-O-benzoyl-1-O-tert-butyl(dimethyl)silyl-2-deoxy-β-d-arabino-hexopyranose with suitably blocked derivatives of methyl α-d-glucopyranoside and methyl α-isomaltoside, respectively.

An antigenic polysaccharide from Campylobacter coli serotype O:30. Structure of a teichoic acid-like antigenic polysaccharide associated with the lipopolysaccharide.

A water-soluble antigenic polysaccharide of high M(r) associated with the lipopolysaccharide has been isolated from phenol-water extraction of cells of Campylobacter coli serotype O:30. The polysaccharide and oligosaccharide degradation products formed on O-dephosphorylation and by periodate oxidation followed by reduction have been investigated by one- and two-dimensional 1H, 13C, and 31P NMR. It is concluded that the antigenic polysaccharide has a teichoic acid-like structure with a poly-Ribitol phosphate, [5-Ribitol-1-P]n, backbone with side chains at O-2 of O-(6-deoxy-beta-D-talo-heptopyranosyl)-(1-->4)-(2-acetylamino-2-deoxy-beta-D- glucopyranosyl) units. The structure is unusual in Gram-negative bacteria and is unique in possessing 6-deoxy-D-talo-heptose as a constituent sugar. Evidence for the relationship of the antigenic polysaccharide to the lipopolysaccharide of low M(r) is discussed.

Composites of starch and poly(ethylene‐co‐acrylic acid). Complexing between polymeric components

AbstractExtrusion‐blown film prepared from a semidry mixture of starch and poly(ethylene‐co‐acrylic acid) (EAA) cannot be sharply separated into its polymeric components by selective solvent extraction, and the two polymers have the outward appearance of being compatible. Also, the starch portion is resistant to enzyme attack, and starch domains are not visible by SEM. Further studies were therefore made on the starch–EAA system to determine reasons for the apparent compatibility between the two polymers, and evidence for polymer complex formation was obtained. Combination of aqueous ammonia solutions of starch and EAA led to an increase in viscosity, and a coprecipitate of starch and EAA separated from solution. Moreover, solvent extraction would not separate physical mixtures of starch and EAA prepared from aqueous solutions. Although both the linear (amylose) and branched (amylopectin) components of starch formed an apparent complex with EAA, a low molecular weight starch fraction and a high molecular weight dextran (a polysaccharide with α‐(1→6) linked glucopyranosyl units) did not. These observations support the theory that a helical inclusion complex is formed from starch and EAA, which is similar to the well‐known complexes produced from starch and fatty acids.

Location of O-acetyl groups in the heteropolysaccharide of the cactus Pereskia aculeata

The complex polysaccharide of the leaves of Pereskia aculeata is highly branched, containing units of arabinofuranose, arabinopyranose, galactopyranose, galactopyranosyluronic acid, and rhamnopyranose. Glucopyranose units are also present. The location of 25 molar % of acetate ester groups was determined using modified Bouveng procedures, one of the changes being the use of refluxing methanolic sodium methoxide for the removal of N-methyl- N-phenylcarbamoyl groups. With the aid of g.l.c.-m.s. on a capillary column of DB-210, which separated the various isomeric mono-, di-, and tri- O-methyl arabinitol acetates, and by examination of e.i. fragmentation patterns of various derivatives deuterated at C-1, the O-acetyl groups were located. They were found mainly as monosubstituents at O-2 and O-3 of nonreducing arabinofuranosyl end-groups and at O-2 of 4- O-substituted galacto- and gluco-pyranosyl units.

Starfish saponins. Part 5. Structure of sepositoside A, a novel steroidal cyclic glycoside from the starfish Echinaster sepositus

The toxic major saponin from the starfish Echinaster sepositus, has been completely characterized. The structure is unique having as it does both a Δ7,3β,6β-dioxygenated-23-oxosteroidal moiety and a sugar moiety [β-D-glucopyranosyl-(1→2)-β-D-galactopyranosyl-(1→2)-β-D-glucuronopyranosyl] which bridges the C-3 and C-6 atoms of the steroid. The 3β-hydroxy-group of the steroid forms an O-acetal linkage with the glucuronate unit, while the HO–C(6‴) of the glucopyranosyl unit is attached to C-6 of the aglycone, forming a 6β-O-ethereal linkage.

Flocculant and chemical properties of a polysaccharide from Pullularia pullulans.

An extracellular polysaccharide, PP-floc, was synthesized from glucose by Pullularia pullulans (or Aureobasidium pullulans) in a pilot plant batch fermentor containing 175 liters of culture medium. At 58 h of fermentation, the concentration of PP-floc was 1.03 g/100 ml, giving a 25.8% conversion of initial glucose to polysaccharide. The flocculant activity of the culture medium increased during the fermentation process and reached its maximum at 50 h of culture age. Less PP-floc (0.33 lb/ton of slimes [approximately 149.7 g/0.907 t]) was required to give the same flocculant activity as a synthetic polymer of acrylamide, Separan NP-10 (0.5 lb/ton of slimes [approximately 226.8 g/0.907 t]), at all temperatures from 25 to 100 C. The degree of inactivation of PP-floc and Separan NP-10 at elevated temperatures was almost identical, and they were completely inactivated at about the same temperature (80 C). PP-floc also gave better compaction of slimes than Separan NP-10 at all temperatures tested. PP-floc was soluble in water and its specific optical rotation was [alpha](D) (25) + 194 degrees in water (c, 0.4). PP-floc contained 83.3% carbohydrate, 3.2% protein, and 8.1% water. Glucose was found to be the principal sugar monomer with traces (>5%) of galactose and mannose present. Structural studies on the fractions of purified polysaccharide by methylation and by periodate oxidation techniques prove that PP-floc is linear and composed of alpha-(1 --> 4) and alpha-(1 --> 6) glucopyranosyl units in the approximate ratio of 2:1. The action of pullulanase on crude PP-floc suggested the ordered arrangement of two consecutive alpha-(1 --> 4)-linked glucopyranosyl units flanked by alpha-(1 --> 6)-linked glucopyranose residues.

Flocculant and Chemical Properties of a Polysaccharide from Pullularia pullulans

An extracellular polysaccharide, PP-floc, was synthesized from glucose by Pullularia pullulans (or Aureobasidium pullulans) in a pilot plant batch fermentor containing 175 liters of culture medium. At 58 h of fermentation, the concentration of PP-floc was 1.03 g/100 ml, giving a 25.8% conversion of initial glucose to polysaccharide. The flocculant activity of the culture medium increased during the fermentation process and reached its maximum at 50 h of culture age. Less PP-floc (0.33 lb/ton of slimes [approximately 149.7 g/0.907 t]) was required to give the same flocculant activity as a synthetic polymer of acrylamide, Separan NP-10 (0.5 lb/ton of slimes [approximately 226.8 g/0.907 t]), at all temperatures from 25 to 100 C. The degree of inactivation of PP-floc and Separan NP-10 at elevated temperatures was almost identical, and they were completely inactivated at about the same temperature (80 C). PP-floc also gave better compaction of slimes than Separan NP-10 at all temperatures tested. PP-floc was soluble in water and its specific optical rotation was [alpha](D) (25) + 194 degrees in water (c, 0.4). PP-floc contained 83.3% carbohydrate, 3.2% protein, and 8.1% water. Glucose was found to be the principal sugar monomer with traces (>5%) of galactose and mannose present. Structural studies on the fractions of purified polysaccharide by methylation and by periodate oxidation techniques prove that PP-floc is linear and composed of alpha-(1 --> 4) and alpha-(1 --> 6) glucopyranosyl units in the approximate ratio of 2:1. The action of pullulanase on crude PP-floc suggested the ordered arrangement of two consecutive alpha-(1 --> 4)-linked glucopyranosyl units flanked by alpha-(1 --> 6)-linked glucopyranose residues.

Disposition of D‐glucopyranosyl units on the surfaces of crystalline elementary fibrils of cotton cellulose

AbstractThe results from two different chemical approaches to study the disposition of D‐glucopyranosyl segments of the cellulose chains on the surfaces of microstructural units accessible to chemical reagents in cotton cellulose are compared, correlated, and rationalized. These studies provide the basis for a suggested disposition of D‐glucopyranosyl units in the crystalline surfaces of elementary fibrils, for a proposed arrangement of hydrogen bonds on these surfaces, and for estimates of the size of the elementary fibrils.

Network Formation in Cotton Cellulose Modified with Tris (1-aziridinyl) phosphine Oxide

Cotton cellulose modified with tris(1-aziridinyl)phosphine oxide (APO) at various levels of reaction was examined for network development (cross-link formation) by determination of the soluble (sol) and insoluble (gel) fractions in cupriethylenediamine hydroxide (Cuene), by observation of dissolution and swelling of thin cross sections in Cuene, and by measurement of the extent of swelling of the gel fraction in Cuene. The behavior of the APO-modified cotton cellulose is compared to that of cotton cross-linked with formaldehyde in a bake-cure process. Relatively low effectiveness of APO in developing a network structure in cotton cellulose is indicated by the results of this study. Mathematical analysis of the sol-gel data by means of the Charlesby-Pinner and Schultz equations leads to numerical estimates of the extent of Cuene-stable covalent bond formation between APO residues and the glucopyranosyl units of cotton cellulose; the results are in agreement (within a factor of two) with the results of organic component analysis reported in the preceding papers.

Extent of Formation of Ether Linkages Between Tris(1-aziridinyl)phosphine Oxide and Cotton Cellulose

Cotton cellulose modified with tris(1-aziridinyl)phosphine oxide (APO) was prepared with and without zinc fluoborate catalyst. The modified cotton samples were hydrolyzed. Attempts to detect the expected 0-(2-aminoethyl)-D-glucopy- ranoses were complicated by reactions between the functional group at C-1 of the glucose unit and the amine function of the substituent. The ratio of substituents in the 2-0-, 3-0-, and 6-0-positions of the glucopyranosyl units in samples of APO-modified cotton cellulose could be measured when the amino groups were converted to hydroxyl groups by diazo tization prior to hydrolysis. The APO-modified cotton cellulose prepared with zinc fluoborate catalysis and containing 3.08, 5.77, and 14.62% APO exhibited substituent ratios of 0.23:0.21:1.00, 0.29:0.26:1.00, and 0.38:0.37:1.00, respec tively, at the 2-0-, 3-0-, and 6-0-positions. A sample of APO-modified cotton cellulose (6.38% APO) prepared without catalyst exhibited a substituent distribution of 0.65:0.35:1.00. The actual DS values of these samples were estimated to be 0.0040, 0.0071, 0.0084, and 0.0098 for the fabrics containing 3.08, 5.77, 6.38, and 14.62% of incorporated APO, respectively.

Formation and structure of extracellular glucans produced by Claviceps species.

SUMMARY: Submerged cultures of Claviceps fusiformis (Loveless) became progressively viscous during the incubation because of the production of an extracellular polysaccharide. The polysaccharide was shown to be a branched glucan with a β1 → 3 linked main chain having single glucopyranosyl units at intervals along it in the β1 → 6 configuration. For most of the media investigated growth at 27° and between pH 5 and 6 was accompanied by glucan production, which ceased when growth was arrested by lack of nutrient. The glucan was re-metabolized by the fungus only to a limited extent as the culture aged; the degree of branching varied during the culture period. The unit amount of glucan synthesized was not affected by numerous successive subculturings over a period of several months, but the product from the later cultures had a greater degree of branching. Branched glucans of similar structure to the above were also detected in low concentration in the natural sclerotia. The presence of β1 → 3 linked glucans in the cell walls of this and other fungal strains examined was also indicated.

Reagent effects on distribution of methylsulfonylethyl substituents in the D-glucopyranosyl unit of cotton cellulose

The distribution of methylsulfonylethyl substituents at the 2-O-, 3-O-, and 6-O-positions of the monosubstituted D-glucopyranosyl unit of cotton cellulose was found to be a function of the specific reagent and the reaction conditions. The distribution is dependent upon the extent to which rate or equilibrium of reaction at the individual hydroxyl groups is the controlling factor. Under conditions which approach equilibrium in the reaction of methyl vinyl sulfone with cotton cellulose, the ratio of 2-O- to 6-O-substitution is 0.14:1.0. A variety of precursors for methyl vinyl sulfone (i.e., 2-(methylsulfonyl)-ethanol, [2-(rnethylsulfonyl)ethyl]pyridinium chloride, 2-bromoethyl methyl sulfone, and to-[2-(methylsulfonyl)ethyl]ether) react with cotton cellulose under non-equilibrium conditions to generate ratios of 2-O- to 6-O-substitutions as high as 0.44:1.0. The effect of diffusion of reagents into the cotton fiber upon the distribution of substituents is clearly evident in these reactions. Specific modifications of the process of reaction of methyl vinyl sulfone or 2-(methylsulfonyl)ethanol with cotton cellulose yield ratios of substituents in the 2-O- to 6-O-positions as high as 0.8:1.0; this ratio is similar to those which characterize certain rate-controlled Williamson etherification reactions with cotton cellulose.

Substrate specificity of mycodextranase.

MYCODEXTRAN (nigeran) is an unbranched polysaccharide composed of a regular alternating sequence of α–(1rarr;3) and α–(1→4) linked glucopyranosyl units. It is produced in the mycelia of various species of moulds1. Reese and Mandels have recently reported2 the isolation and partial purification of an inducible glucanase (mycodextranase) produced in the culture filtrates of selected species of fungi grown on a medium containing mycodextran as a carbon source. The enzyme is an endoglucanase that hydrolyses nigeran to produce hexameric and tetrameric units which are subsequently hydrolysed to produce the disaccharide nigerose (O–α–D–glucopyranosyl–(1→3)–D–glucose) as the final product2.