Showing papers on "Pyranose published in 2017"
TL;DR: The dynamic nature of boronate ester bonds formed with vicinal diols present on alginate pyranose rings provided remarkable self-healing, injectable and multi-stimuli responsive properties to the material.
128 citations
TL;DR: In this article, a novel approach to stereoselective synthesis of C-aryl glycosides capitalizing on the highly stereospecific reaction of anomeric nucleophiles was described.
Abstract: Stereoselective manipulations at the C1 anomeric position of saccharides are one of the central goals of preparative carbohydrate chemistry. Historically, the majority of reactions forming a bond with anomeric carbon has focused on reactions of nucleophiles with saccharide donors equipped with a leaving group. Here, we describe a novel approach to stereoselective synthesis of C-aryl glycosides capitalizing on the highly stereospecific reaction of anomeric nucleophiles. First, methods for the preparation of anomeric stannanes have been developed and optimized to afford both anomers of common saccharides in high anomeric selectivities. We established that oligosaccharide stannanes could be prepared from monosaccharide stannanes via O-glycosylation with Schmidt-type donors, glycal epoxides, or under dehydrative conditions with C1 alcohols. Second, we identified a general set of catalytic conditions with Pd2(dba)3 (2.5 mol%) and a bulky ligand (JackiePhos, 10 mol%) controlling the β-elimination pathway. We demonstrated that the glycosyl cross-coupling resulted in consistently high anomeric selectivities for both anomers with mono- and oligosaccharides, deoxysugars, saccharides with free hydroxyl groups, pyranose, and furanose substrates. The versatility of the glycosyl cross-coupling reaction was probed in the total synthesis of salmochelins (siderophores) and commercial anti-diabetic drugs (gliflozins). Combined experimental and computational studies revealed that the β-elimination pathway is suppressed for biphenyl-type ligands due to the shielding of Pd(II) by sterically demanding JackiePhos, whereas smaller ligands, which allow for the formation of a Pd-F complex, predominantly result in a glycal product. Similar steric effects account for the diminished rates of cross-couplings of 1,2-cis C1-stannanes with aryl halides. DFT calculations also revealed that the transmetalation occurs via a cyclic transition state with retention of configuration at the anomeric position. Taken together, facile access to both anomers of various glycoside nucleophiles, a broad reaction scope, and uniformly high transfer of anomeric configuration make the glycosyl cross-coupling reaction a practical tool for the synthesis of bioactive natural products, drug candidates, allowing for late-stage glycodiversification studies with small molecules and biologics.
83 citations
TL;DR: Right-handed helical poly amido-saccharides (PASs) with β-N-(1→2)-d-amide linkages are synthesized by the anionic ring-opening polymerization of an altrose β-lactam monomer (alt-Lactam), showcasing the ability to direct solution conformation of polymers through monomer design.
Abstract: The design and synthesis of amide-linked saccharide oligomers and polymers, which are predisposed to fold into specific ordered secondary structures, is of significant interest. Herein, right-handed helical poly amido-saccharides (PASs) with β-N-(1→2)-d-amide linkages are synthesized by the anionic ring-opening polymerization of an altrose β-lactam monomer (alt-lactam). The right-handed helical conformation is engineered into the polymers by preinstalling the β configuration of the lactam ring in the monomer via the stereospecific [2+2] cycloaddition of trichloroacetyl isocyanate with a d-glycal possessing a 3-benzyloxy group oriented to the α-face of the pyranose. The tert-butylacetyl chloride initiated polymerization of the alt-lactam proceeds smoothly to afford stereoregular polymers with narrow dispersities. Birch reduction of the benzylated polymers gives water-soluble altrose PASs (alt-PASs) in high yields without degradation of the polymer backbone. Circular dichroism analysis shows the alt-PASs adopt a right-handed helical conformation in aqueous solutions. This secondary conformation is stable over a wide range of different conditions, such as pH (2.0 to 12.0), temperature (5 to 75 °C), ionic salts (2.0 M LiCl, NaCl, and KCl), as well as in the presence of protein denaturants (4.0 M urea and guanidinium chloride). Cytotoxicity studies reveal that the alt-PASs are nontoxic to HEK, HeLa, and NIH3T3 cells. The results showcase the ability to direct solution conformation of polymers through monomer design. This approach is especially well-suited and straightforward for PASs as the helical conformations formed result from constraints imposed by the relatively rigid and sterically bulky repeating units.
33 citations
TL;DR: Permethylation proved to be a useful technique for the analysis of ketopentoses and pharmaceuticals soluble in dimethyl sulfoxide, while the oximation/pertrimethylsilylation method prevailed as the more promising, overall, derivatization method.
29 citations
TL;DR: New water-soluble chitosan derivatives (WSCh), with similar functional properties to those presented by native Ch, are obtained by Maillard reaction (MR) between glucosamine (GA), enhancing its potential application as carrier material for bioactive compounds.
28 citations
TL;DR: The X-ray crystal structure of NagBb is reported, representing the first GH129 family structure, solved by the single-wavelength anomalous dispersion method based on sulfur atoms of the native protein.
21 citations
TL;DR: Cyclic phosphonium anhydrides generated from bis-phosphine oxides and trifluoromethanesulfonic anhydride are shown as general coupling reagents in a dehydrative glycosylation reaction of C1-hemiacetals.
Abstract: Cyclic phosphonium anhydrides generated from bis-phosphine oxides and trifluoromethanesulfonic anhydride are shown as general coupling reagents in a dehydrative glycosylation reaction of C1-hemiacetals. This reaction protocol is characterized by a broad substrate scope and high yields, including reactions of O-, C-, N-, and S-based nucleophiles with furanose, pyranose, and deoxysugar donors.
21 citations
TL;DR: The results of a systematic study oriented at determining the ring-inversion properties of all d-hexopyranoses in the form of monosaccharides, O1-methylated monosACcharides and homotrisaccharide are presented.
Abstract: Among the descriptors of the molecular structure of carbohydrates, the conformation of the pyranose ring is usually the most problematic one to tackle. We present the results of a systematic study oriented at determining the ring-inversion properties of all D-hexopyranoses in the form of monosaccharides, O1-methylated monosaccharides and homotrisaccharides. Contrary to the existing studies, based either on molecular mechanics force fields or on conformational search within ab initio potentials, we combine the structural information from molecular dynamics simulations performed within the GROMOS 56a6CARBO_R force field and use it in a subsequent geometry optimization procedure, performed at the DFT level of theory. This two-step procedure allows avoiding errors resulting from overestimating the contribution of the hydrogen bond-rich, low-energy structures that are not abundant in aqueous solutions. The calculated anomeric ratios and the populations of staggered conformers of the hydroxymethyl group are in satisfactory agreement with the experimental data. Regarding the ring-inversion properties, for the first time, we achieved good agreement of the ab initio-derived data for all hexopyranoses with the experimentally inferred Angyal scheme and with the NMR-inferred populations of ring conformers. The same computational methodology allows determination of the influence of functionalization (methylation or glycosylation) on the ring-inversion properties which includes the influence of the anomeric effect, enhanced upon O1-functionalization. In general, the correlation between ring-inversion properties of unfunctionalized monomers and those of O1-methylated, O1-glycosylated, O4-glycosylated and O1,O4-diglycosylated monomers is qualitatively (but not quantitatively) compatible with that predicted by the classical force fields.
16 citations
TL;DR: Twenty 1,4-disubstituted-triazole nucleosides were synthesized in good yields using the copper catalyzed ‘Click’ reaction between azido-modified pento- or hexopyranoses and alkyne-bearing pyrimidine or purine nucleobases to create a library of compounds with potential bioactivities.
Abstract: With the aim to create a library of compounds with potential bioactivities by combining special characteristics of two important groups such as nucleobases and carbohydrates, twenty 1,4-dis...
14 citations
TL;DR: The pyranose members of the pyrrolomorpholine spiroketal family have been synthesized by stereoselective spirocyclizations of a common glycal precursor, leading to the identification of novel 2-hydroxy analogues with more potent antioxidant activities than the natural products.
Abstract: The pyranose spiroketal natural products pollenopyrroside A and shensongine A (also known as xylapyrroside A, ent-capparisine B) have been synthesized by stereoselective spirocyclizations of a common C1-functionalized glycal precursor. In conjunction with our previously reported syntheses of the corresponding furanose isomers, this provides a versatile family-level synthesis of the pyrrolomorpholine spiroketal natural products and analogues. In rat mesangial cells, hyperglycemia-induced production of reactive oxygen species, which is implicated in diabetic nephropathy, was inhibited by pollenopyrroside A and shensongine A with mid-μM IC50 values, while unnatural C2-hydroxy analogues exhibited more potent, sub-μM activity.
12 citations
TL;DR: The more axial-rich donors in skew and boat conformations are thus preorganized closer to the assumed transition state in these glycosylation reactions for differently protected β-linked 2-O-glycosylated glucosyl donors carrying bulky tert-butyldimethylsilyl groups to different extents.
Abstract: To advance the field of glycobiology, efficient synthesis methods of oligosaccharides and glycoconjugates are a requisite. In glycosylation reactions using superarmed donors, both selectivity and reactivity issues must be considered, and we herein investigate these aspects for differently protected β-linked 2-O-glycosylated glucosyl donors carrying bulky tert-butyldimethylsilyl groups to different extents. The acceptors in reactions being secondary alcohols presents a challenging situation with respect to steric crowding. Conformational pyranose ring equilibria of the superarmed disaccharide donors with axial-rich substituents contained skew and boat conformations, and three-state models were generally assumed. With NIS/TfOH as the promotor, 2,6-di-tert-butyl-4-methylpyridine as the base, and a dichloromethane/toluene solvent mixture, ethyl 1-thio-β-d-glucosyl disaccharide donors having 6-O-benzyl group(s) besides tert-butyldimethylsilyl groups were efficiently coupled at −40 °C to the hydroxyl group at p...
TL;DR: A systematic set of N-glycosylation site mutants was investigated in this work, regarding expression efficiency, enzyme activity and stability, and this site was shown to be the only one that is essential for functional recombinant expression of the enzyme.
TL;DR: It is confirmed that the A. meleagris genes pdh2 and pdh3 indeed encode CAZy class AA3_2 pyranose dehydrogenases, and their kinetic properties differed significantly for the model electron acceptor substrates tested.
Abstract: Multigenicity is commonly found in fungal enzyme systems, with the purpose of functional compensation upon deficiency of one of its members or leading to enzyme isoforms with new functionalities through gene diversification. Three genes of the flavin-dependent glucose-methanol-choline (GMC) oxidoreductase pyranose dehydrogenase (AmPDH) were previously identified in the litter-degrading fungus Agaricus (Leucoagaricus) meleagris, of which only AmPDH1 was successfully expressed and characterized. The aim of this work was to study the biophysical and biochemical properties of AmPDH2 and AmPDH3 and compare them with those of AmPDH1. AmPDH1, AmPDH2 and AmPDH3 showed negligible oxygen reactivity and possess a covalently tethered FAD cofactor. All three isoforms can oxidise a range of different monosaccarides and oligosaccharides including glucose, mannose, galactose and xylose, which are the main constituent sugars of cellulose and hemicelluloses, and judging from the apparent steady-state kinetics determined for these sugars, the three isoforms do not show significant differences pertaining to their reaction with sugar substrates. They oxidize glucose both at C2 and C3 and upon prolonged reaction C2 and C3 double-oxidized glucose is obtained, confirming that the A. meleagris genes pdh2 (AY753308.1) and pdh3 (DQ117577.1) indeed encode CAZy class AA3_2 pyranose dehydrogenases. While reactivity with electron donor substrates was comparable for the three AmPDH isoforms, their kinetic properties differed significantly for the model electron acceptor substrates tested, a radical (the 2,2'-azino-bis[3-ethylbenzothiazoline-6-sulphonic acid] cation radical), a quinone (benzoquinone) and a complexed iron ion (the ferricenium ion). Thus, a possible explanation for this PDH multiplicity in A. meleagris could be that different isoforms react preferentially with structurally different electron acceptors in vivo.
TL;DR: In this article, the pyranose ring structure and the hydrogen bonding between water molecules and phosphonate groups were used to determine the minimum energy structure of NDCF membranes and the addition of n water molecules (n = 1-10).
Abstract: This research aims to calculate energetics parameters, hydrogen bonding, characteristics local hydration, and proton transfer in phosphorylated nata de coco (NDCF) membrane using ab initio method. The minimum energy structure of NDCF membranes and the addition of n water molecules (n = 1-10) determined at the B3LYP/6-311G** level indicates that proton dissociation requires a minimum of four water molecules. Dissociated protons stabilize with the formation of (hydronium, Zundel, Eigen) ions. Calculation of the interaction energy with n water molecules indicates an increasingly negative change in energy (ΔE) and enthalpy (ΔH), and hence an increasingly positive interaction with water molecules. This interaction facilitates the transfer of protons in the membrane matrix. Calculation of the rotational energy at the center of C-O indicates that the pyranose ring structure, with a maximum barrier energies of ~ 12.5 J/mol, is much more flexible than the aromatic backbones of sulfonated poly(phenylene) sulfone ( sPSO 2 ) and the polytetrafluoroethylene (PTFE) backbones in perfluorosulfonic acid ionomers (PFSA). These energy calculations provide the basis that the flexibility of the pyranose ring and the hydrogen bonding between water molecules and phosphonate groups influence the transfer of protons in the membrane of NDCF.
TL;DR: The protein structure of a mutated P2O, T169S (Thr169 is replaced by Ser), in solution was studied by means of molecular dynamics simulation and analyses of photoinduced electron transfer from Trp168 to excited isoalloxazine (Iso*), and was compared with wild type (WT).
Abstract: Pyranose 2-oxidase (P2O) from Trametes multicolor contains FAD as cofactor, and forms a tetramer. The protein structure of a mutated P2O, T169S (Thr169 is replaced by Ser), in solution was studied by means of molecular dynamics simulation and analyses of photoinduced electron transfer (ET) from Trp168 to excited isoalloxazine (Iso*), and was compared with wild type (WT) P2O. Hydrogen bonding between Iso and nearby amino acids was very similar as between T169S and WT protein. Distances between Iso and Tyr456 were extremely heterogeneous among the subunits, 1.7 (1.5 in WT) in subunit A (Sub A), 0.97 (2.2 in WT) in Sub B, 1.3 (2.1 in WT) in Sub C, 1.3 nm (2.0 in WT) in Sub D. Mean values of root of mean square fluctuation over all residues were greater by four times than those in WT. This suggests that the protein structure of T169S is much more flexible than that of WT. Electrostatic (ES) energies between Iso anion in one subunit and ionic groups in the entire protein were evaluated. It was found that more than 50% of the total ES energy in each subunit is contributed from other subunits. Reported fluorescence decays were analyzed by a method as WT, previously reported. Electron affinities of Iso* in T169S were appreciably higher than those in WT. Static dielectric constants near Iso and Trp168 were also quite higher in T169S than those in WT. This article is protected by copyright. All rights reserved.
TL;DR: A systematic comparative conformational analysis of all eight aldohexose isomers using DFT methods reveals changes in anomeric and ring conformational preference upon reduction or oxidation at the C-6 position for several sugars.
Abstract: Knowledge of multi-dimensional carbohydrate structure is essential when delineating structure-function relationships in the development of analytical techniques such as ion mobility-mass spectrometry and of carbohydrate-based therapeutics, as well as in rationally modifying the chemical and physical properties of drugs and materials based on sugars. Although monosaccharides are conventionally presumed to adopt the canonical 4C1 chair conformation, it is not well known how altering the substituent identity around the pyranose ring affects the favored conformational state. This work provides a comprehensive and systematic computational comparison of all eight aldohexose isomers in the gas phase with reduction and oxidation at the C-6 position using density functional theory (M05-2X/cc-pVTZ(-f)//B3LYP/6-31G**) to determine the conformational and anomeric preference for each sugar in the gas phase. All 6-deoxyhexose and aldohexose isomers favored the 4C1 chair conformation, while oxidation at C-6 showed a shift in equilibrium to favor the 1C4 chair for β-alluronic acid, β-guluronic acid, and β-iduronic acid. The anomeric preference was found to be significantly affected by a remote change in oxidation state, with the alternate anomer favored for several isomers. These findings provide a fundamental platform to empirically test steric and electronic effects of pyranose substituents, with the goal of formulating straightforward rules that govern carbohydrate reactivity and drive quicker, more efficient syntheses. Graphical abstract A systematic comparative conformational analysis of all eight aldohexose isomers using DFT methods (M05-2X/cc-pVTZ(-f)) reveals changes in anomeric and ring conformational preference upon reduction or oxidation at the C-6 position for several sugars.
TL;DR: Gas phase, isolated (fructose + (H2O)n)- (n = 1-5) cluster anions mainly exist as open chain structures with conformational and positional isomers in the present experiments, consistent with the fructose solution tautomeric equilibrium with neutral fructose pyranose being the preponderant species.
Abstract: Photoelectron spectroscopy (PES) and density functional theory (DFT) based calculations are executed to characterize gas phase, isolated (fructose + (H2O)n)- (n = 1-5) anionic species produced using a matrix assisted laser desorption ionization (MALDI) method. Gas phase, isolated (fructose + (H2O)n)- (n = 1-5) cluster anions mainly exist as open chain structures with conformational and positional isomers in the present experiments. Some cyclic structures of (fructose + (H2O)n)- (n = 3, 4) are apparently present in the experiments and their VDEs can contribute to the lower energy shoulders of PES features observed for (fructose + (H2O)n)- (n = 3, 4). Cyclic (fructose + (H2O)n)- (n = 1-5) clusters have the added electron as dipole bound, whereas open chain structures have the added electron in a valence orbital. Water molecules in open chain anions predominantly interact with the (1)C side (including (1)OH, (2)O, and (3)OH) of fructose-: they finally form a quasi-cubic structure with OH groups and carbonyl O in the most stable structures for (fructose + (H2O)4)- and (fructose + (H2O)5)- cluster anions. Water molecules solvating cyclic anions form water-water hydrogen bond networks that preferentially interact with OH groups at the (1), (2), and (3) positions of fructose pyranose anions, and the (3), (4), and (6) positions of fructose furanose anions. Structures of neutral (fructose + (H2O)n) (n = 1-5) have pyranose structures as the lower energy isomers rather than open chain structures: this observation is consistent with the fructose solution tautomeric equilibrium with neutral fructose pyranose being the preponderant species. Water molecules also tend to form water-water hydrogen bond networks, interacting with OH groups at (1), (2), and (3) positions for neutral pyranose conformations.
Patent•
25 Jul 2017
TL;DR: In this paper, a method for preparing flaxseed gum oligosaccharides by a hydrogen peroxide oxidation degradation technology is described, and the FGOS obtained in the invention are a semisolid viscous substance, have a light reddish brown color and special fragrance, can be easily dissolved in water, are insoluble in ethanol and other organic solvents, can easily absorb moisture, are a typical carbohydrate substance, and contain uronic acid.
Abstract: The invention discloses a method for preparing flaxseed gum oligosaccharides by a hydrogen peroxide oxidation degradation technology. The flaxseed gum oligosaccharides (FGOSs) are prepared from commercial flaxseed gum by adopting a high pressure assisted hydrogen peroxide oxidation degradation technology through dynamic dissolving, oxidative degradation, suction filtering, decolorizing, ultrafiltration, dialysis, concentration and freeze-drying. The FGOSs obtained in the invention are a semisolid viscous substance, have a light reddish brown color and special fragrance, can be easily dissolved in water, are insoluble in ethanol and other organic solvents, can easily absorb moisture, are a typical carbohydrate substance, and contain uronic acid; the FGOSs have uniform components, the average molecular weight is 1047 Da, the FGOS have a pyranose ring structure, belong to pyranose, and are composed of the following seven monosaccharides: rhamnose, fucose, arabinose, xylose, mannose, galactose and glucose, and the FGOS have certain anti-oxidation ability, and have a high removal rate on hydroxyl free radicals, DPPH free radicals, ABTS free radicals and superoxide anion free radicals.
TL;DR: Using the method of IR spectroscopy, it was ascertained that in pectinates and alginates of polyvalent metals, the coordination between cations Pb2+, Cu2+, Zn2+, Cr3+ and Ni2+ formed asymmetrical structures with carboxyl groups as discussed by the authors.
Abstract: Using the method of IR spectroscopy
it was ascertained that in pectinates and alginates of polyvalent metals the coordination
bonds between cations Pb2+, Cu2+, Zn2+, Cr3+,
Mn2+, Fe2+, Co2+, Ni2+ and the oxygen
atoms of carboxyl and hydroxyl groups, pyranose cycle and glycosidic linkage of
polyuronides, the water molecules are formed. It was also ascertained that Cu2+ cations form asymmetrical structures with carboxyl groups of polyuronides (monodentate
ligands) and cations of other metals—symmetrical structures with carboxyl groups
of polyuronides (bidentate ligands).
TL;DR: The stereoselective peracetylation of α-d-xylose and α-l-arabinose using a combination of triethylamine and acetic anhydride in the presence or absence of a catalytic amount of dimethylaminopyridine (DMAP) is described.
TL;DR: In this article, a novel reaction cascade involving a Lewis acid-induced migration of an isopropylidene protecting group followed by the formation of a pyranose or furanose ring and subsequent reduction of the hemiacetal is described.
Abstract: A novel reaction cascade involving a Lewis acid-induced migration of an isopropylidene protecting group followed by the formation of a pyranose or furanose ring and subsequent reduction of the hemiacetal is described. Depending on the reaction conditions, as well as, the stereochemistry of the substrate, polyhydroxylated tetrahydrofurans or tetrahydropyrans can be obtained in reasonable yields. The synthons used in this transformation were prepared via a highly stereoselective one-pot tandem reaction, consisting of a 1,4-Michael addition of vinylmagnesium bromide to d -glucose-derived cyclohexenone followed by aldol reaction with 2,3- O -isopropylidene- d -glyceraldehyde.
Dissertation•
01 Jan 2017
TL;DR: In this paper, the authors present a list of figures, tables, and nomenclature for a collection of tables and figures from the book "Acknowledgements and acknowledgements:
Abstract: ....................................................................................................................................... i Acknowledgements .................................................................................................................. iii List of Figures ............................................................................................................................ ix List of Tables ........................................................................................................................ xxiii Nomenclature.......................................................................................................................... xxv Abbreviations ....................................................................................................................... xxvii Chapter
Dissertation•
01 Jan 2017
Patent•
26 Jun 2017
TL;DR: In this article, a double-bonded polysaccharide derivatives comprising a double bond in the positions 4 and 5 of the pyranose cycle were used to improve carcinoma cell viability.
Abstract: The invention relates to the preparation of new polysaccharide derivatives comprising a double bond in the positions 4 and 5 of the pyranose cycle. The method of preparation consists in the oxidation of OH group in the position 6 to an aldehyde, followed by the elimination to form a double —C═C— bond in the positions 4 and 5, and the final reduction of the aldehyde group in the position 6 into the original alcohol. The derivatives of polysaccharides prepared according to the invention show an enhanced antioxidant activity and some of them also a selective negative influence on carcinoma cell viability. (formula) where R represents —NH—CO—CH 3 or —OH.