Carbohydrate Research (v.343, #2)
Exploring specificity of glycosyltransferases: synthesis of new sugar nucleotide related molecules as putative donor substrates
by Amira Khaled; Olga Piotrowska; Katarzyna Dominiak; Claudine Augé (pp. 167-178).
We investigated the specificity of glycosyltransferases toward donor substrates in two complementary directions. First we prepared simple N-acetyl-α-d-glucosamine 1-diphosphates: methyl-(2-acetamido-2-deoxy-α-d-glucopyranosyl)-diphosphate, benzyl-(2-acetamido-2-deoxy-α-d-glucopyranosyl)-diphosphate, 4-phenylbutyl-(2-acetamido-2-deoxy-α-d-glucopyranosyl)-diphosphate, by the coupling of the corresponding activated alkyl phosphates with N-acetyl-α-d-glucosamine 1-phosphate. These diphosphates as well as 2-acetamido-2-deoxy-α-d-glucopyranose 1-diphosphate, tested as donors of N-acetylglucosamine in a reaction catalyzed by Neisseria meningitidis N-acetylglucosaminyltransferase ( LgtA), proved to be devoid of activity. Evaluated as inhibitors, only 2-acetamido-2-deoxy-α-d-glucopyranose 1-diphosphate showed some inhibitory activity with an IC50 value of 7mM.In the second approach, we prepared sugar nucleotide mimics having the diphosphate bridge replaced by the oxycarbonylaminosulfonyl linker. The surrogate of GDP-Fuc was synthesized as a 9:1 α/β anomeric mixture, in 40% yield, starting from chlorosulfonyl isocyanate, perbenzylatedl-fucopyranose, and a guanosine derivative, protected on the exocyclic amine and secondary hydroxyl functions of ribose. Then two deprotection steps, hydrogenolysis and enzymatic hydrolysis catalyzed by penicillin G amidase afforded the target molecule to be tested as fucose donor with recombinant human α-(1→3/4)-fucosyltransferase (FucT-III). Tested as a 4:1 α/β anomeric mixture, both in the absence and in the presence of cationic cofactors, this new guanosine fucose conjugate proved to be ineffective. Its inhibitory activity toward FucT-III evaluated through a competition fluorescence assay was very poor (IC50 value of 20mM). The surrogate of UDP-GlcNAc that was already known as its protected acetylated derivative, tested as N-acetylglucosamine donor with LgtA in the presence of Mn2+ turned out not to be active either.
Keywords: Sugar nucleotides; Donor substrate; Surrogate; Fucosyltransferase; N; -Acetylglucosaminyltransferase; Inhibitor
Synthesis of two repeat units corresponding to the backbone of the pectic polysaccharide rhamnogalacturonan I
by Dominic Reiffarth; Kerry B. Reimer (pp. 179-188).
A tetrasaccharide corresponding to a sequence of the rhamnogalacturonan I backbone has been synthesized. This synthesis relies on only two protected monosaccharides and proceeds through a common disaccharide intermediate. Synthesis of this tetrasaccharide has been designed to allow for the addition of branching elements at the 4-positions of the rhamnosyl units, or further chain elongation at the 2-position.
Keywords: Rhamnogalacturonan I; Galacturonic acid; cis; -Glycoside
A convenient synthesis of the C-1-phosphonate analogue of UDP-GlcNAc and its evaluation as an inhibitor of O-linked GlcNAc transferase (OGT)
by Jan Hajduch; Ghilsoo Nam; Eun Ju Kim; Roland Fröhlich; John A. Hanover; Kenneth L. Kirk (pp. 189-195).
The C-1-phosphonate analogue of UDP-GlcNAc has been synthesized using an α-configured C-1-aldehyde as a key intermediate. Addition of the anion of diethyl phosphate to the aldehyde produced the hydroxyphosphonate. The configuration of this key intermediate was determined by X-ray crystallography. Deoxygenation, coupling of the resulting phosphonic acid with UMP and deprotection gave the target molecule as a di-sodium salt. This analogue had no detectable activity as an inhibitor of (OGT).
Keywords: O; -GlcNAc transferase; N; -Acetylglucosamine; UDP-GlcNAc; Phosphate isostere; OGT inhibition
Preparation of glycoconjugates by dialkyl squarate chemistry revisited
by Shu-jie Hou; Rina Saksena; Pavol Kováč (pp. 196-210).
The methyl 6-hydroxyhexanoyl glycoside of lactose was treated with each of 1,2-diaminoethane or hydrazine hydrate, and the corresponding amino amide4 and acyl hydrazide13, were treated with each of squaric acid dimethyl, diethyl, dibutyl, and didecyl esters. The monoesters were conjugated to bovine serum albumin (BSA) at different concentrations of hapten using 0.05 and 0.5M pH 9 borate buffer. Maximum loading was achieved faster, and the conjugation efficiency was higher, when the conjugation was conducted at higher concentrations of both hapten and buffer. Conjugations involving haptens14–17 prepared from hydrazide13 were generally slower and less efficient than those with compounds5–8, which were made from amino amide4. Maintaining pH 9 during conjugation was found to be the most important factor in ensuring that the conjugation was a fast, highly efficient, and reproducible process. When the pH of the conjugation mixture fell during the reaction, resulting in decreased reaction rate or even termination of the conjugation process, the normal course of the conjugation process could be restored by addition of buffer salts. Hydrolysis studies with monoesters formed from amino amide4 under conjugation conditions showed that decyl ester8 was the most stable and that the methyl compound5 was the one most readily hydrolyzed. The stability of monoesters prepared from hydrazide13 was similar and comparable to the decyl ester prepared from4. No definite advantage was found for the use of any of the four dialkyl squarate reagents (methyl-, ethyl-, butyl-, and decyl-) for conversion of carbohydrate derivatives to species amenable for conjugation. Nevertheless, dimethyl squarate seemed to be the most convenient reagent because it is a crystalline, easy to handle, and commercially available material with very good reactivity.
Keywords: Conjugate; Neoglycoconjugate; Squaric acid diester; 5-Methoxycarbonyl-β-lactoside; SELDI TOF-MS
Indirect approach to C-3 branched 1,2- cis-glycofuranosides: synthesis of aceric acid glycoside analogues
by Marcelo T. de Oliveira; David L. Hughes; Sergey A. Nepogodiev; Robert A. Field (pp. 211-220).
Aceric acid (3- C-carboxy-5-deoxy-α-l-xylofuranose) residues are present in pectic polysaccharide rhamnogalacturonan II (RG II) in the form of synthetically challenging 1,2- cis-glycofuranosides. To access synthetic fragments of RG II incorporating aceric acid, a four-step procedure based on C-2 epimerisation of initially prepared 1,2- trans-glycofuranoside was developed. Readily available derivatives of branched-chainl-lyxofuranose bearing a 3- C-vinyl group as a masked 3- C-carboxyl group were investigated as potential precursors of aceric acid units. In the first step of the procedure, installation of a participating group at C-2 of the furanose ring ensured stereocontrol of the O-glycosylation, which was carried out with the thioglycoside of 2- O-acetyl-3,5-di- O-benzyl-3- C-vinyl-l-lyxofuranose. After the glycosylation step, the 2- O-acetyl group was removed, the free 2-OH group was oxidised and the resulting ketone was finally reduced to form the C-3-vinyl-l-xylofuranoside. The use of L-Selectride in the key reduction reaction was essential to achieve the required stereoselectivity to generate 1,2- cis-furanoside.
Keywords: Glycofuranosides; Branched-chain sugars; Aceric acid; Rhamnogalacturonan II
WAXS and13C NMR study of Gluconoacetobacter xylinus cellulose in composites with tamarind xyloglucan
by Tracey J. Bootten; Philip J. Harris; Laurence D. Melton; Roger H. Newman (pp. 221-229).
- Model composites, produced using cellulose from stationary cultures of the bacterium Gluconoacetobacter xylinus and tamarind xyloglucan, were examined by wide-angle X-ray scattering (WAXS) and CP/MAS solid-state13C NMR spectroscopy. The dominant crystallite allomorph of cellulose produced in culture media with or without xyloglucan was cellulose Iα (triclinic). The presence of xyloglucan in the culture medium reduced the cross-section dimensions of the cellulose crystallites, but did not affect the crystallite allomorph. However, when the composites were refluxed in buffer, the proportion of cellulose Iβ allomorph increased relative to that of cellulose Iα. In contrast, cellulose Iα remained the dominant form when cellulose, produced in the absence of xyloglucan, was then heated in the buffer. Hence the presence of xyloglucan has a profound effect on the formation of the cellulose crystallites by G. xylinus.
Keywords: Plant cell walls; Xyloglucan; Cellulose; Gluconoacetobacter xylinus; Solid-state; 13; C NMR; WAXS (wide-angle X-ray scattering)
Preparation of chitosan–nylon-6 blended membranes containing silver ions as antibacterial materials
by Yunli Ma; Tao Zhou; Changsheng Zhao (pp. 230-237).
Chitosan–nylon-6 blended membranes containing silver ions were prepared in two steps, and their antibacterial properties with variation of the chitosan content, pH value and concentration of the silver nitrate solution used to prepare the membranes were systematically discussed.Chitosan–nylon-6 blended membranes were prepared by combining solvent evaporation and a phase inversion technique, and then used to chelate silver ions. Gram-positive bacteria ( Staphylococcus aureus) and Gram-negative bacteria ( Escherichia coli) were used to study the antibacterial properties of the membranes. Fourier-transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) indicated hydrogen-bond interactions between chitosan and nylon-6. From the scanning electron microscopy (SEM) pictures, it was observed that with the increase of nylon-6 content, the blended membrane gradually became a material with porous morphology. After chelating silver ions, the tensile strength of the membranes increased. The antibacterial activity with the variation of chitosan content, the pH value and the concentration of the silver nitrate solution used to prepare Ag+-loaded membranes were investigated systematically. The results indicated that the chitosan–nylon-6 blended membranes with Ag+ were antibacterial to both Gram-positive bacteria and Gram-negative bacteria. The antibacterial activity improved with the increased chitosan content due to the larger amount of silver ions loaded. The antibacterial property of the chitosan–nylon-6 blended membranes could be primarily attributed to the content of chitosan and silver ions as well as the surface morphology of the membranes.
Keywords: Chitosan; Nylon-6; Silver ions; Antibacterial property
Characterization of the lipopolysaccharide from a wbjE mutant of the serogroup O11 Pseudomonas aeruginosa strain, PA103
by Biswa Choudhury; Russell W. Carlson; Joanna B. Goldberg (pp. 238-248).
The lipopolysaccharide (LPS) of a wbjE mutant of Pseudomonas aeruginosa PA103, a serogroup O11 strain consists of both high and low molecular weight (HMW and LMW) LPSs. The HMW LPS consisted exclusively of rhamnan A-band LPS and no B-band LPS was detected in the wbjE mutant. Interestingly, the LMW LPS from the wbjE mutant showed that it contained a variety of oligosaccharides, each with two or three phosphate groups present as mono- or pyrophosphates.These oligosaccharides consisted of the complete core octasaccharide.Display OmittedThe GalN residue was present as an N-acetylated residue in all of these oligosaccharides except the tetrasaccharide in which it is present as an N-alanylated residue. None of these oligosaccharides contained either ad- orl-Fuc pNAc residue. These results are discussed with regard to the role of wbjE in the biosynthesis of P. aeruginosa PA103 B-band LPS.
Keywords: Pseudomonas aeruginosa; Lipopolysaccharide; Inner core; wbjE; Biosynthesis
Inhibition of acid-catalyzed depolymerization of cellulose with boric acid in non-aqueous acidic media
by Haruo Kawamoto; Shinya Saito; Shiro Saka (pp. 249-255).
Boric acid inhibited the acid-catalyzed depolymerization of cellulose in sulfolane, a non-aqueous medium, at high temperature. Formation of the dehydration products such as levoglucosenone, furfural, and 5-hydroxymethyl furfural were also effectively inhibited. Similar inhibition was observed for cellooligosaccharides and starch, although the glucosidic bonds in methyl glucopyranosides and methyl cellobioside were cleaved to form α-d-glucofuranose cyclic 1,2:3,5-bisborate.
Keywords: Cellulose; Starch; Acid-catalyzed depolymerization; Boric acid; Sugar borate; Cellooligosaccharide
Structural characterization of the acetylated heteroxylan from the natural hybrid Paulownia elongata/ Paulownia fortunei
by Virgínia M.F. Gonçalves; Dmitry V. Evtuguin; M. Rosário M. Domingues (pp. 256-266).
The heteroxylan from the hybrid Paulownia elongata/ Paulownia fortunei is an O-acetyl-(4- O-methylglucurono)xylan with an acetylation degree (DS) of 0.59 and a molecular weight ( Mw) of 29kDa. The heteroxylan backbone is composed by (1→4)-linked β-d-xylopyranosyl units (Xyl p) partially ramified with terminal (1→2)-linked 4- O-methyl-α-d-glucuronosyl (MeGlc pA) and a small proportion of α-d-glucuronosyl (Glc pA) residues in a molar ratio of Xyl p:(MeGlc pA+Glc pA) of 20:1. Roughly half of the β-d-xylopyranosyl units in the backbone are acetylated: 3-O-acetylated (22mol%), 2-O-acetylated (23mol%) or 2,3-di-O-acetylated (7mol%). ESI-MS and MALDI-MS studies of partially hydrolyzed heteroxylan revealed a random distribution of O-Ac and MeGlc pA within the backbone. However, the frequency of substitution with O-Ac along the backbone is not uniform and the molecular regions that did not contain MeGlc pA substituents possessed an acetylation degree significantly lower than the average DS of the xylan.
Keywords: Paulownia; Xylan; Structural analysis; Electrospray; MALDI; NMR spectroscopy
Preparation and metal-binding behaviour of chitosan functionalized by ester- and amino-terminated hyperbranched polyamidoamine polymers
by Rongjun Qu; Changmei Sun; Chunnuan Ji; Chunhua Wang; Hou Chen; Yuzhong Niu; Chengju Liang; Qiyi Song (pp. 267-273).
A series of insoluble chitosan (CTS) derivatives were prepared by grafting ester- and amino-terminated dendrimer-like polyamidoamine (PAMAM) into CTS using a divergent method by repeating two processes: (1) Michael addition of methyl acrylate (MA) to surface amino groups, and (2) amidation of the resulting esters with ethylenediamine (EDA). Their structures were characterized by infrared spectra (IR) and wide-angle X-ray diffraction (WAXD). The adsorption capabilities of the products for Au3+, Pd2+, Pt4+, Ag+, Cu2+, Zn2+, Hg2+, Ni2+, and Cd2+ were studied. The results showed that the products exhibited better adsorption capabilities for Au3+ and Hg2+ than for other metal ions, and the adsorption capabilities of amino-terminated products were higher than those of ester-terminated ones. Also it was observed that a high percentage of grafting of PAMAM into CTS does not ensure a high adsorption capacity.
Keywords: Chitosan; Polyamidoamine-typed hyperbranched polymer; Preparation; Adsorption; Metal ion
Methanolysis of ethyl esters of N-acetyl amino acids catalyzed by cyclosophoraoses isolated from Rhizobium meliloti
by Heylin Park; Seunho Jung (pp. 274-281).
Methanolysis of four ethyl esters, N-acetyl-l-phenylalanine ethyl ester, N-acetyl-l-tyrosine ethyl ester, N-acetyl-l-tryptophan ethyl ester, and ethyl phenylacetate was catalyzed by a mixture of microbial cyclooligosaccharides termed cyclosophoraoses isolated from Rhizobium meliloti. Cyclosophoraoses [cyclic-(1→2)-β-d-glucans, collectively ‘Cys’] are a mixture of large-ring molecules consisting of various numbers of glucose residues (17–27) linked by β-(1→2)-glycosidic bonds. Cys as a catalytic carbohydrate enhanced the methanolysis about 233-fold for N-acetyl-l-tyrosine ethyl ester in comparison with a control. The effect of dry organic solvents on the methanolysis of N-acetyl-l-tyrosine ethyl ester was investigated by high-performance liquid chromatography (HPLC), and it was found that the rate enhancement correlated closely with the hydrophobicity of the solvent.
Keywords: N; -Acetyl amino acids; Ethyl esters; Methanolysis; Rhizobium meliloti; Cyclosophoraoses; Catalytic oligosaccharides
Preparation and spectroscopic characterization of methoxy poly(ethylene glycol)-grafted water-soluble chitosan
by Young-Il Jeong; Don-Gon Kim; Mi-Kyeong Jang; Jaw-Woon Nah (pp. 282-289).
The object of this study was to test the solubility of a methoxy poly(ethylene glycol) (MPEG)-grafted chitosan copolymer in organic solvents and aqueous solution. Water-soluble chitosan with low molecular weight (LMWSC) was used in a PEG-graft copolymerization. The MPEG was conjugated to chitosan using 4-dicyclohexylcarbodimide (DCC), and N-hydroxysuccimide (NHS). Introduction of PEG was confirmed by1H and13C NMR spectroscopy and FT-IR spectroscopy. The degree of substitution (DS) of MPEG into chitosan was calculated from1H NMR data and also by estimating the molecular weight (MW) using gel permeation chromatography (GPC). The DS values obtained from1H NMR spectroscopy and GPC were similar, indicating that MPEG-grafted LMWSC was synthesized and properly characterized. Furthermore, the introduction of PEG into chitosan increases the solubility in aqueous solutions over a range of pH values (4.0–11.0) and organic solvents such as DMF, DMSO, ethanol, and acetone.
Keywords: Water-soluble chitosan; Poly(ethylene glycol); Aqueous solubility; Organic solvent solubility; Graft copolymer
The impact of dilute sulfuric acid on the selectivity of xylooligomer depolymerization to monomers
by Rajeev Kumar; Charles E. Wyman (pp. 290-300).
The disappearance of xylose and xylooligosaccharides with degrees of polymerization (DP) ranging from 2 to 5 was followed at 160°C with sulfuric acid added to adjust the pH from near neutral to 1.45, and the impact on the yields of lower DP xylooligomers and xylose monomer was determined. In addition, the experimental data for the disappearance of these xylooligomers was kinetically modeled assuming first-order reaction kinetics for xylose degradation and xylooligomer hydrolysis to evaluate how the pH affected the selectivity of monomer formation from xylooligomers and direct oligomer degradation to unknown products. The yield of xylose from xylooligomers increased appreciably with increasing acid concentration but decreased with increasing xylooligomer DP at a given acid concentration, resulting in more acid being required to realize the same xylose yields for higher DP species. For example, the maximum xylose yields were 49.6%, 28.0%, 13.2% and 3.2% for DP values of 2, 3, 4, and 5, respectively, at pH 4.75. Kinetic modeling revealed that all the xylooligomers disappeared at a higher rate compared to xylose monomer and the disappearance rate constant increased with DP at all pH. The kinetics for lower DP oligomers of 2 and 3 showed that these species directly degrade to unknown compounds in the absence of acid. On the other hand, higher oligomers of DP 4 and 5 exhibited negligible losses to degradation products at all pH. Therefore, only xylooligomers of DP 2 and 3 were found to directly degrade to undesired products in the absence of acid, but more work is needed to determine how higher DP species behave. This study also revealed that the source of water and the material used for the construction of the reactor impacted xylose degradation kinetics.
Keywords: Depolymerization; Degradation; Selectivity; Xylooligomers; Xylose; Yield
Determination of the structure and molecular weights of the exopolysaccharide produced by Lactobacillus acidophilus 5e2 when grown on different carbon feeds
by Andrew P. Laws; Marcus J. Chadha; Mariana Chacon-Romero; Valerie M. Marshall; Mohammed Maqsood (pp. 301-307).
A novel exopolysaccharide is produced from Lactobacillus acidophilus 5e2 when grown in skimmed milk supplemented with glucose: Lactobacillus acidophilus 5e2 when grown on skimmed milk, skimmed milk supplemented with sodium formate and skimmed milk supplemented with glucose secretes a branched heteropolysaccharide having a weight average molecular weight less than 450kDa. The exopolysaccharide has a heptasaccharide repeat unit and is composed ofd-glucose,d-galactose and N-acetyl-d-glucosamine in the molar ratio 3:3:1. Using chemical techniques and 1D and 2D-NMR spectroscopy the polysaccharide has been shown to possess the following repeat unit structure:Display Omitted
Keywords: Exopolysaccharide; NMR; LAB; Molecular weight; Lactobacillus acidophilus
FT-IR spectra of alginic acid block fractions in three species of brown seaweeds
by David Leal; Betty Matsuhiro; Miriam Rossi; Francesco Caruso (pp. 308-316).
The homopoly-l-guluronic blocks presented in the IR spectra two characteristics bands at 812 and 781cm−1.Sodium alginates obtained by alkaline extraction of Lessonia flavicans, Desmarestia ligulata and Desmarestia distans (Phaeophyta) from southern Chile were partially hydrolyzed with HCl. Each alginate gave three fractions that were characterized using FT-IR spectroscopy. The fractions soluble in 0.3M HCl presented in the fingerprint region four vibrations at around 960, 911, 890 and 815cm−1 that were assigned to heteropolymeric blocks. The fractions soluble at pH 2.85 showed bands at around 948, 888 and 820cm−1 attributed to homopolymannuronic acid blocks, the first band is resolved in the second-derivative spectra into two bands at 951 and 936cm−1. The fractions insoluble at pH 2.85 presented four bands at around 947, 903, 812 and 781cm−1, which were assigned to homopolyguluronic acid blocks. For some samples, the second derivative FT-IR spectra showed new bands indicating the presence of other structures, in low proportions. Structures deduced by FT-IR spectroscopy were corroborated by solution1H and13C NMR spectroscopy. Two-dimensional spectra were collected to confirm the fine structure of the hetero- and homopolymeric fractions. A geometrically optimized model for the disaccharide α-l-gulopyranuronosyl-(1→4)-α-l-gulopyranuronic acid was calculated using density functional theory; good agreement was obtained between its corresponding calculated vibrations and the experimental bands assigned to homopolyguluronic acid blocks.
Keywords: Alginic acids; Block composition; FT-IR characteristic bands; DFT-calculated vibrations
The applicability of an amidated polysaccharide hydrogel as a cartilage substitute: structural and rheological characterization
by Gemma Leone; Maurizio Delfini; Maria Enrica Di Cocco; Anna Borioni; Rolando Barbucci (pp. 317-327).
An amidic derivative of a carboxymethylcellulose-based hydrogel was obtained and characterized in terms of amidation degree. NMR studies and FT-IR imaging spectroscopy demonstrated that the reaction allowed a polymer to be obtained that was characterized by a regular distribution of amidic groups along the polysaccharide chains. Through this regularity, a homogenous three-dimensional scaffold was obtained, which maintained the thixotropic property of the linear polysaccharide.
Keywords: Amidic carboxymethylcellulose; Hydrogel; NMR; FT-IR Imaging
Effect of pH on the association behavior in aqueous solutions of pig gastric mucin
by Atoosa Maleki; Géraldine Lafitte; Anna-Lena Kjøniksen; Krister Thuresson; Bo Nyström (pp. 328-340).
In this study, dynamic light scattering (DLS), turbidity, and rheo-small angle light scattering (rheo-SALS) methods have been utilized to examine the impact of pH (1⩽pH⩽7) on aqueous solutions of noncommercial purified pig gastric mucin. The asymmetric flow field-flow fractionation (AFFFF) measurements established that the mucin sample has a high molecular weight and is polydisperse. DLS measurements on dilute solutions of mucin disclosed large interchain aggregates at pH 2, where the polymer has a low charge density or is uncharged. At lower or higher values of pH, mucin is charged and the tendency of forming interpolymer complexes is affected. In the semidilute concentration regime, pronounced junction zones (‘lumps’ of polymer) are evolved and a heterogeneous connected network is formed at pH 2, whereas the association structures are disintegrated (smaller ‘lumps’) at lower or higher pH values due to electrostatic repulsive interactions, and a more homogeneous network is evolved. The DLS and viscosity results at pH 1 indicate the development of a fragmented network, composed of contracted chains that are decorated by some positive charges. The effect of shear flow on the structure of semidilute solutions of mucin was investigated with the aid of rheo-SALS methods. The scattered intensity revealed a strong upturn at low values of the wave vector ( q) for mucin solutions at pH 2 and pH 4, which suggests the evolution of large association domains. At these pH values, a flow-induced anisotropy in the 2D SALS patterns in the form of elliptical shapes was observed at high shear rates.
Keywords: Purified pig gastric mucin; Dynamic light scattering; Rheo-small angle light scattering; Effect of pH; Associations
Structural studies of a methyl galacturonosyl-methoxyxylan isolated from the stem of Lagenaria siceraria (Lau)
by Kaushik Ghosh; Krishnendu Chandra; Sadhan K. Roy; Subhas Mondal; Debabrata Maiti; Debsankar Das; Arnab K. Ojha; Syed S. Islam (pp. 341-349).
A water-soluble polysaccharide was isolated from the aqueous extract of the stem of Lagenaria siceraria. The polysaccharide was found to be constituted of methyld-galacturonate, 2- O-methyl-d-xylose, andd-xylose in a ratio of 1:1:1. On the basis of total acid hydrolysis, methylation analysis, periodate oxidation, NMR studies (1H,13C, 2D-COSY, TOCSY, NOESY, HSQC, and HMBC), and MALDI-TOF MS analysis, the structure of the repeating unit of the polysaccharide is determined asDisplay Omitted
Keywords: Lagenaria siceraria; Polysaccharide; Structure; NMR spectroscopy; MALDI-TOF MS analysis
The effect of sodium chloride on molecular mobility in amorphous sucrose detected by phosphorescence from the triplet probe erythrosin B
by Yumin You; Richard D. Ludescher (pp. 350-363).
Phosphorescence from the triplet probe erythrosin B provides spectroscopic characteristics such as emission energy and lifetime that are specifically sensitive to molecular mobility of the local environment. This study used phosphorescence of erythrosin B to investigate how variation in NaCl content modulated the mobility of the amorphous sucrose matrix over the temperature range from 5 to 100°C. Addition of NaCl increased the emission energy and the energy difference with excitation at the absorption maximum and the red edge, and increased the lifetime by reducing the non-radiative decay rate in the glass as well as in the undercooled liquid in a concentration dependent manner, indicating that NaCl decreased the matrix molecular mobility. Emission energy and lifetime increased with increasing NaCl content up to a maximum at NaCl/sucrose mole ratio of ∼0.5; above 0.5mole ratio, the effect of NaCl was less significant and appeared to be opposed by increasing plasticization by residual water. Changes in the width of the distribution of the emission energy and lifetime and variation in the lifetime with excitation and emission wavelength indicated that NaCl increased the spectral heterogeneity and thus increased the extent of dynamic site heterogeneity. These results are consistent with a physical model in which sodium and chloride ions interact with sucrose OH by ion–dipole interactions, forming clusters of less mobile molecules within the matrix.
Keywords: Sucrose; NaCl; Amorphous solid; Molecular mobility; Phosphorescence; Erythrosin BAbbreviations; Ery B; erythrosin B; FWHM; full width at half maximum; T; g; glass transition temperature; T; g; ′; glass transition temperature of the maximally freeze-concentrated solution
Heterogeneity in iota-carrageenan molecular structure: insights for polymorph II→III transition in the presence of calcium ions
by Srinivas Janaswamy; Rengaswami Chandrasekaran (pp. 364-373).
The structural details underscore unexpected flexibility in double helix polymer morphology of polymorph III, and packing arrangement offers an elegant transition mechanism from II.Iota-carrageenan is used in pharmaceutical and food applications due to its ability to complex with other hydrocolloids and proteins. Six distinct cation dependent allomorphs, consistent with its versatile functionality, have so far been observed in the solid state. In this contribution, X-ray structural details of calcium iota-carrageenan (form III) are reported. The polysaccharide retains the half-staggered, parallel, 3-fold, right-handed double helix stabilized by interchain hydrogen bonds from O–2H and O–6H in the Gal p units. Results show that there are four helices, rather than one in I or three in II, organized in a larger pseudotrigonal unit cell of dimensions a=27.44, c=13.01Å, and γ=120°. The four helices have similar core structures, but their sulfate group orientations are quite different. Fifteen calcium ions and 64 water molecules hold the helices together and promote helix–helix interactions. The results portray how the helices would shuffle around in an orchestrated manner to yield calcium iota-carrageenan III from II.
Keywords: Sulfated polysaccharide; Iota-carrageenan; X-ray diffraction; Packing arrangement
Molecular structures of glycal-based bolaamphiphiles: analysis of crystal packing and hydrogen-bond networks
by Nathan C. Tice; Sean Parkin; Joseph J. Bozell (pp. 374-382).
The crystal structures for the glycal bolaamphiphiles, 1,12-bis-(2,3-α-d- erythro-hex-2-enopyranosyloxy)-dodecane (1) and 1,12-bis-(2,3-α-d- threo-hex-2-enopyranosyloxy)-dodecane (2), were determined by single-crystal X-ray analysis. The structure for1 showed that the α:α and α:β diastereomers co-crystallized, with occupancy factors determining an isomeric ratio of 69:31. The pyranose rings for both structures are oriented away from each other and adopt a conventional glycal geometry. The head groups are nearly gauche to the hydrophobic chain, which adopts an all-trans zigzag conformation. Bolaamphiphile1 packs in anti-parallel layers, while bolaamphiphile2 displays a parallel arrangement of layers. Both structures display a three-dimensional hydrogen-bonding network involving the hydroxylic substituents on the head groups. The high similarity in large-scale solid state structures between1 and glucosamide bolaamphiphile3, and2 and galactosamide bolaamphiphile4 suggest a strong dependence on head group stereochemistry, and that only a few, key intermolecular interactions between head groups are necessary in controlling the ultimate structure observed. The solid state results may have implications for understanding the intermolecular forces directing nanoscale self-assembly in solution.
Keywords: X-ray; Bolaamphiphile; Crystal structure; Crystal packing; Hydrogen-bond network; Glucal; galactal; Self-assembly; Nanoscale materials
Acid-catalysed rearrangement of glycosyl trichloroacetimidates: a novel route to glycosylamines
by Kim Larsen; Carl Erik Olsen; Mohammed Saddik Motawia (pp. 383-387).
A novel route to glycosylamines has been developed. Treatment of glycosyl trichloroacetimidates with TMSOTf under glycosylation conditions, but in the absence of an acceptor, resulted in complete rearrangement of the trichloroacetimidates into the corresponding N-protected-glycosylamines. Reductive cleavage of the trichloroacetyl groups using sodium borohydride provided the desired glycosylamine products.
Keywords: Chapman rearrangement; Glycosylamine; Reduction; Trichloroacetimidate
Synthesis of N-bridgehead heterocycles from saccharide benzimidazoles
by Mohammed A.E. Sallam; Viggo Waagen; Thorleif Anthonsen (pp. 388-391).
Treatment ofd- arabino-tetritol-1-yl-benzimidazole with p-toluenesulfonyl chloride (1molequiv) in pyridine, afforded the N-bridgehead heterocycles, 2 R,3 R,4 S-trihydroxy-1:2:3:4-tetrahydropyridino[1,2- a]benzimidazole. The structure of the latter compound was determined by acylation,1H, and13C NMR spectroscopy and mass spectrometry.
Keywords: d; -; arabino; -Benzimidazole; N-Bridgehead heterocycles; 1:3-Diazaline
The structure of the O-specific polysaccharide of the lipopolysaccharide from Pantoea agglomerans strain FL1
by Alessio Cimmino; Guido Marchi; Giuseppe Surico; Anna Hanuszkiewicz; Antonio Evidente; Otto Holst (pp. 392-396).
A neutral O-specific polysaccharide consisting ofd-rhamnose was obtained by mild acid hydrolysis of the lipopolysaccharide of the plant pathogenic bacterium Pantoea agglomerans strain FL1, a common epiphyte of many plant species, and associated with Pseudomonas savastanoi pv. savastanoi in young and apparently intact olive knots. By means of compositional and methylation analyses, and NMR spectroscopy, the chemical repeating unit of the polymer was identified as a linear tetrasaccharide of the structure:Display Omitted
Keywords: Olive knot; Pantoea agglomerans; Lipopolysaccharide; O-specific polysaccharide; NMR spectroscopy
X-ray crystallographic study of several 2′-deoxy-β-d-ribonucleosides with 1-deazapurine-derived aglycones
by Jens Müller; Fabian-Alexander Polonius; Eva Freisinger; Elisa Gil Bardají (pp. 397-403).
A series of 2′-deoxy-β-d-ribonucleosides with deazapurine-derived aglycones has been prepared and structurally characterized by X-ray crystallography.The 2′-deoxy-β-d-ribonucleosides of 1,3-deazapurine (benzimidazole (1)), 1-deazapurine (both 1 H-imidazo[4,5- b]pyridine (2) and 3 H-imidazo[4,5- b]pyridine (3)), and 6-benzoylamino-1-deazapurine (7-benzoylamino-3 H-imidazo[4,5- b]pyridine (4)) have been prepared and structurally characterized by X-ray crystallography. Especially compounds1–3 can serve as artificial nucleosides that may substitute 2′-deoxy adenosine because they lack the exocyclic amino group and one or two of the endocyclic nitrogen atoms and hence have a much smaller potential to engage in hydrogen bonds. In the latter respect, they are candidates for nucleosides in metal-ion mediated base pairs. The unit cell of compound3 contains two crystallographically independent molecules. Compound4 was crystallized from methanol and water, respectively, giving rise to two different solvates. Despite the closely related aglycones, the sugar conformations in1–4 are found to be highly variable (1:2 T1;2:3 T2;3:3 E and E4;4:2 E and2 T3). The structures reported here confirm that there is no simple correlation between the sugar conformation and the character of the nucleoside, and they will hopefully contribute to a better understanding of the complex interplay of different effects that are in control of the conformational equilibrium.
Keywords: 2′-Deoxyribonucleosides, structure; 1-Deazapurine; 1,3-Deazapurine; Benzimidazole; 1-Deazaadenine, protected derivative
Synthesis and geometry of methyl (methyl 4- O-acetyl-3-azido-2,3-dideoxy-α/β-d- arabino- and -α/β-d- ribo-hexopyranosid)uronates
by Dorota Tuwalska; Artur Sikorski; Beata Liberek (pp. 404-411).
The synthesis of methyl (methyl 4- O-acetyl-3-azido-2,3-dideoxy-α/β-d- arabino- and -α/β-d- ribo-hexopyranosid)uronates is presented. High resolution1H and13C NMR spectral data for all diastereoisomers and single-crystal X-ray diffraction analysis for methyl (methyl 3-azido-2,3-dideoxy-β-d- arabino-hexopyranosid)uronate are reported. The planarity of the 4-OAc and 5-COOMe groups as well as the orientations of the aglycone and azide groups in the crystal lattice is discussed. The influence of the 5-COOMe group on the pyranose ring conformation is considered.
Keywords: Sugar amino acid; X-ray diffraction; Anomeric effect; Mesomeric effect; Hybridization; Conformational equilibrium