Pyranose Unit Research Articles

Crystal structures of O-acetylated 2-acylamino-2-deoxy- d-galactose derivatives

The X-ray structures of 1,3,4,6-tetra- O-acetyl-2-deoxy-α- d-galactopyranoside derivatives with four different 2-(acylamino) substituents have been determined with Mo K α radiation at 123 K. The structure of the 2-acetylamino derivative and of its acyl-homologs with a 2-(propanoylamino)-, 2-(butanoylamino)-, and 2-(2-methyl-propanoylamino)-group crystallized in the monoclinic space group C2. The pyranose unit of all compounds has the usual 4 C 1 shape. The different orientations of the 6- O-acetyl-groups are discussed. Conformations of the acylamino-group are compared to those found in the crystal structure of N-acetyl-α- d-galactosamine.

Mapping the binding of synthetic disaccharides representing epitopes of chlamydial lipopolysaccharide to antibodies with NMR.

A NMR study of the binding of the synthetic disaccharides alpha-Kdo-(2-->4)-alpha-Kdo-(2-->O)-allyl 1 (Kdo, 3-deoxy-D-manno-oct-2-ulopyranosonic acid) and alpha-Kdo-(2-->8)-alpha-Kdo-(2-->O)-allyl 2, representing partial structures of the lipopolysaccharide epitope of the intracellular bacteria Chlamydia, to corresponding monoclonal antibodies (mAbs) S23-24, S25-39, and S25-2 is presented. The conformations of 1 bound to mAbs S25-39 and of 2 bound to mAbs S23-24 and S25-39 were analyzed by employing transfer-NOESY (trNOESY) and QUIET-trNOESY experiments. A quantitative analysis of QUIET-trNOESY buildup curves clearly showed that S25-39 recognized a conformation of 1 that was similar to the global energy minimum of 1, and significantly deviated from the conformation of 1 bound to mAb S25-2. For disaccharide 2, only a qualitative analysis was possible because of severe spectral overlap. Nevertheless, the analysis showed that all mAbs most likely bound to only one conformational family of 2. Saturation transfer difference (STD) NMR experiments were then employed to analyze the binding epitopes of the disaccharide ligands 1 and 2 when binding to mAbs S23-24, S25-39, and S25-2. It was found that the nonreducing pyranose unit was the major binding epitope, irrespective of the mAb and the disaccharide that were employed. Individual differences were related to the engagement of other portions of the disaccharide ligands.

Pd-Catalyzed coupling reaction of glycosylamines with 6-chloropurines: Synthesis of 6-(β- d-mannopyranosylamino)-9 H-purine and its β- d-gluco isomer, N-glycoside models for spicamycin and septacidin

The first example of preparation of 6-(β- d-mannopyranosylamino)-9 H-purine ( 8), whose N-glycosidic linkage corresponds to a natural antibiotic, spicamycin, by Pd-catalyzed coupling reaction of a mannopyranosylamine with 9-protected-6-chloropurine, followed by deprotection, is described. Its β- d-gluco isomer ( 11) was also synthesized. This work established the procedure to construct the novel N-glycoside, in which the pyranose unit is connected to the amino group at C(6) of adenine moiety.

Amidine pseudodisaccharides

The synthesis of several aminoglucopyranose-based amidine pseudodisaccharides is described. They may serve as glycosidase inhibitors by virtue of structural similarities to both the reducing and non-reducing pyranose units involved in glycolysis.

X‐ray photoelectron spectroscopy and infra‐red studies of X‐ray‐induced beam damage of cellulose, ethyl cellulose and ethyl‐hydroxyethyl cellulose

AbstractThe cellulose derivatives ethyl cellulose and ethyl‐hydroxyethyl cellulose (EHEC) have been studied by XPS in the form of solvent‐cast films. All the films, as well as a sample of cellulose used as a standard material, show significant surface degradation on irradiation in the time period consistent with XPS data acquisition. Under the experimental conditions employed here the four materials studied behave similarly, in that a reaction occurs in the cellulose skeleton, resulting in dehydroxylation of some of the pyranose units in the surface layers, with concomitant elimination of molecules of water.An infrared (IR) analysis of the ethyl cellulose and high‐molicular‐weight EHEC films indicates the presence of a strong carbonyl band, no evidence for which is found in the XPS spectra. However, other features of the IR spectra support the proposed dehydroxylation mechanism. The origin of this inconsistency is nuclear but may be attributable to either differences in the surface and bulk degradation products formed or to the detection differences of the XPS and IR techniques.

Phase transitions of the water-xanthan system

The phase transitions of the water-xanthan system are studied using differential scanning calorimetry (d.s.c.). Upon heating, a glass transition, the cold crystallization of water, melting of water and transition from the mesophase to the isotropic liquid were observed for samples with water content ( W c) ranging from 0.5 to 1.4. These transition temperatures vary depending on the water content. The glass transition was observed for water content ranging from 0.5 to 2.0. Enthalpy relaxation was observed to occur after annealing at a temperature lower than the glass transition temperature. From the heat of fusion of water, the amounts of non-freezing ( W nf) and freezing water ( W f) were calculated. There were 50 non-freezing water molecules per repeat unit (four pyranose units). The heat of transition from the mesophase to the isotropic liquid decreased with increasing W c. The heat capacity difference ( ΔC p) between the glassy and liquid states was measured for the system, and it was found that this showed a good correlation with W c. The d.s.c. results indicate that both transitions, the liquid crystalline to the isotropic liquid state and the glass.transition, are caused by the molecular motion of xanthan sorbed on non-freezing water.

Isolation and identification of 3-deoxy- d- threo-hexulosonic acid as a constituent of the lipopolysaccharide of Vibrio parahaemolyticus serotypes O7 and O12

Treatment of the lipopolysaccharide of Vibrio parahaemolyticus serotypes O7 and O12 with mild acid gave a compound which, on the basis of chemical analysis, g.l.c.-m.s., and 1H and 13C-n.m.r. spectroscopy, was characterized as 3-deoxy- d- threo-hexulosonic acid and shown to be present as a terminal non-substituted pyranose unit.

Thermal degradation of model compounds with blocked hemiacetal group related to (4-O-methyl-D-glucurono)-D-xylan

Reduced (4-O-methyl-D-glucurono)-D-xylan and nine methylglycosides related to this polysacharide were studied by dynamic and isothermal thermogravimetry. It could be stated from the results that the thermal stability of saccharides is increasing with increasing number of pyranose units. The models related to (4-O-methyl-D-glucurono)-D-xylan are more thermally stable than the corresponding hexoglycanic models. Rates of gasification of models containing uronic acid methylesters are higher than those of neutral methylglycosides. The rate of polysaccharide gasification was the highest one from all models studied. The supramolecular structure of polysaccharide is dramatically influencing the course of thermal degradation.

Adsorption of water-soluble polymers on high surface area solids.: I. Factors affecting external and interlayer adsorption in carbohydrate polymers

The adsorption of a series of water-soluble carbohydrate polymers on peptized montmorillonite is examined. The investigations emphasize the adsorption characteristics of guaran and cellulose ethers. The ether units consisted of methoxyl and carboxymethyl units and chaining adducts, oxyethylene and oxypropylene, of variable length. The guaran and cellulose ethers varied in molar substitution (M.S.) of adduct per pyranose unit and in the sequence lengths of the unsubstituted pyranose units. Nonionic carbohydrate polymers that were not derivatized with pendant ether linkages adsorbed in proportion to their conformational rigidity. The derivatized carbohydrate polymers containing nonionic ether linkages adsorb in amounts greater than anticipated. The amounts of the segmentally rigid ether derivatives adsorbed on peptized montmorillonite were in proportion to their M.S.; the greater adsorptions were related to an ether—cation interaction. The ion—dipole interaction results in polymer entrapment in the interlayer when the interlayer cation is sodium, ammonium or potassium. It is not observed when the interlayer cation is a constant hexahydrate coordinated calcium ion.

Monomolecular film properties of cellulose and amylose triacetates at the air‐water interface

AbstractSurface pressure‐area isotherms of cellulose triacetate and amylose triacetate at the air‐water interface were determined on a vertical and horizontal film balance. Both polymers show anomalous behavior on the vertical balance, including: higher compressibilities than obtained on the horizontal balance, movement of the vertical plate, and atypical hysteresis of the isotherms.The behavior of the cellulose triacetate film is attributed to heterogeneous gelation of the monolayer at low pressures. A mechanism involving the lateral tilting of pyranose units at the interface and subsequent stabilization of the monolayer by van der Waal's interactions accounts for the properties of this film.A helical conformation for amylose triacetate at the air‐water interface is proposed to explain the low compressibility of this monolayer.

Ionic polysaccharides. IV. Free-rotation dimensions for disaccharide polymers. Comparison with experiment for hyaluronic acid.

AbstractThe root‐mean‐square end‐to‐end distance has been calculated for a model allowing free rotation about glycoside bonds for the general case of polysaccharides having a disaccharide repeating unit. Numerical estimates are given for several naturally occurring structures based on an idealized pyranose unit in the C1 chair conformation. Extrapolation procedures which make use of the intrinsic viscosity [η] in good solvents to obtain unperturbed dimensions do not represent, data for hyaluronic acid very well, especially at low molecular weights. However, order‐of‐magnitude estimates suggest that this polymer behaves similarly to other polysaccharides, and probably has stiffer local structure than typical non‐ionic synthetic polymers. A double logarithmic plot of the product of [η] and M̄w, the weight‐average molecular weight, against the degree of polymerization in the range for M̄w of 104 to 2 × 104 permits a straight‐line fit of available data for all the glycosaminoglycans, including heparin and the chondroitin sulfates, as well as sodium carboxymethyl cellulose. This result suggests similarity of short‐chain hydrodynamic behavior of these polymers.

Configurational statistics of polysaccharide chains. Part I. Amylose

AbstractThe conformational energy of amylose molecule was computed as a function of rotations ϕ and ψ about interunit glycosidic bonds. The characteristic ratio 〈r2〉0/Nl of the mean‐square end‐to‐end distance of the unperturbed chain to the product of n, the number of glucose residues in the chain and the square of the virtual bond length lV = 4.2 Å calculated for amylose chain is about 6.9, which is in good agreement with the experimental value (6.6 ± 0.2). The value of this ratio calculated for free rotation about the inter unit glycosidic bond is 1.1. The conformational map reveals that the rotations of pyranose units about the interunit glycosidic bonds are highly restricted; this tends to lock these units in a preferred orientation. From the probability of occurrence of the glucose residue conformations it is concluded that amylose exists as a random coil with short helical sequences in neutral aqueous solutions.

Infrared spectra of polycarbohydrates and their model systems

AbstractThe relationship of the infrared spectra of polycarbohydrates with their specific structural properties investigated with various model systems, for example, mono‐, di‐saccharides, etc., is discussed.Obtaining the carbohydrate spectra at the temperature of liquid nitrogen has allowed to split the OR group band into distinct components and to find out peculiarities of their low‐temperature shift, and to study the relationship of OR group hydrogen bond with the configuration of certain hydroxyls more thoroughly. Due to the considerable difference in the low‐temperature shift of OR group bands in the probable frequency ranges of intra‐ and intermolecular R bonds have been established as 3350‐3560 cm.−1 and 3100‐3450 cm.−1, respectively. The frequencies and intensities of OR group bands inserted in the H bond are observed to depend strongly upon the configuration of separate hydroxyl groups, suggesting a considerable interaction between the hydroxyls of the pyranose unit. The obtained results furnish ample grounds to conclude that the frequency of OR groups inserted in the hydrogen bond is detennined not only by the energy of the R bond but by the interaction ring, depending on the configuration of separate OR groups.The establishment of a relationship between the mutual spatial arrangement of CR groups and the spectrum in the 800–950 cm.−1 region allowed us to determine the frequency intervals specific for the combinations of axial (A) and equatorial (E) CR groups EA for 810–855 cm.−1; AE for 860–855 cm,−1; AA for 885–920 cm.−1. This allows us to predict the appearance of possible frequencies in the considered region in the process of conformation transitions of the pyranose ring.The investigation of mono‐, di‐, and polysaccharide spectra in the region of CH2 group deformation vibrations and calculation of the potential function of CR2OH group inner rotations permitted us to base the essential possibility of the existence of CR2OH group rotation isomers in carbohydrates and their polymers. The investigation of the spectral feature of crystalline cellulose triesters and triethers has been carried out. It is shown that their spectra are characterized by: an intensity increase of all or the majority of the absorption bands; the selective intensity increase of separate bands; and the appearance of new absorption bands. The intensity increase for many absorption bands is explained by the prevalence of certain types of rotation isomers and the appearance of new bands by the intermolecular interaction in crystals.