Chemical synthesis of sulfated oligosaccharides with a beta-D-Gal-(1-->3)

Combining Computational Chemistry and Crystallography for a Better Understanding of the Structure of Cellulose

The approaches in this article seek to enhance understanding of cellulose at the molecular level, independent of the source and the particular crystalline form of cellulose. Four main areas of structure research are reviewed. Initially, the molecular shape is inferred from the crystal structures of many small molecules that have β-(1→4) linkages. Then, conformational analyses with potential energy calculations of cellobiose are covered, followed by the use of Atoms-In-Molecules theory to learn about interactions in experimental and theoretical structures. The last section covers models of cellulose nanoparticles. Controversies addressed include the stability of twofold screw-axis conformations, the influence of different computational methods, the predictability of crystalline conformations by studies of isolated molecules, and the twisting of model cellulose crystals.

Total Synthesis of the Congested, Bisphosphorylated Morganella morganii Zwitterionic Trisaccharide Repeating Unit

Zwitterionic polysaccharides (ZPSs) activate T-cell-dependent immune responses by major histocompatibility complex class II presentation. Herein, we report the first synthesis of a Morganella morganii ZPS repeating unit as an enabling tool in the synthesis of novel ZPS materials. The repeating unit incorporates a 1,2-cis-α-glycosidic bond; the problematic 1,2-trans-galactosidic bond, Gal-β-(1 → 3)-GalNAc; and phosphoglycerol and phosphocholine residues which have not been previously observed together as functional groups on the same oligosaccharide. The successful third-generation approach leverages a first in class glycosylation of a phosphoglycerol-functionalized acceptor. To install the phosphocholine unit, a highly effective phosphocholine donor was synthesized.

Physicochemical properties and antitumor activities for sulfated derivatives of lentinan

Five fractions of lentinan, a beta-(1-->3)-D-glucan bearing beta-(1-->6)-d-glucopyranosyl branches, were treated with chlorosulfonic acid for 90 min at 60 degrees C in pyridine medium to synthesize water-soluble sulfated derivatives having the substitution degree of 1.44-1.76. The (13)C NMR spectra of the sulfated beta-glucans indicated that the C-6 position was preferentially substituted by the sulfate groups. The values of the weight-average molecular weight (M(w)), radius of gyration (s(2)(z)(1/2)), and intrinsic viscosity ([eta]) of the sulfated lentinan fractions were determined by size-exclusion chromatography with multi-angle laser light scattering (SEC-MALLS) and viscometry in 0.15 M aq NaCl at 25 degrees C, respectively. The dependence of [eta] on M(w) for the sulfated lentinan was found to be [eta]=8.93 x 10(-3)M(w)(0.73+/-0.02) (mL/g) in 0.15 M aq NaCl (for M(w) ranging from 14.6 x 10(4) to 50.4 x 10(4)). On the basis of the Yamakawa-Fujii-Yoshizaki (YFY) theory, the conformational parameters of the sulfated lentinan were calculated as 950 nm(-1) for the molar mass per unit contour length (M(L)), 4.8 nm for the persistence length (q), and 13.9 for the characteristic ratio (C(infinity)), indicating relatively extended single flexible chains in solution. The sulfated glucan fractions exhibited in vitro antiproliferative activities against sarcoma 180 (S-180) cells, and their inhibition ratios were lower than that of the triple-helix lentinan, but higher than that for the one with single random-coil lentinan chains.

Differential O-3/O-4 regioselectivity in the glycosylation of α and β anomers of 6-O-substituted N-dimethylmaleoyl-protected d-glucosamine acceptors

An assessment of the relative O-3/O-4 reactivities of both methyl alpha- and beta-d-glycosides of N-dimethylmaleoyl (DMM) d-glucosamine acceptors protected at O-6 with benzoyl (Bz), benzyl (Bn), and tert-butyldiphenylsilyl (TBDPS) groups is presented using per-O-benzoylated beta-d-galactofuranosyl and per-O-acetylated alpha-d-galactopyranosyl trichloroacetimidates as glycosyl donors. Using the former donor, the alpha anomer of the 6-O-benzoylated compound gave exclusive substitution at O-3, whereas the other two compounds with alpha-configuration kept this site as preferential. The beta anomer of the 6-O-benzoylated compound gave the same amounts of reaction products on O-3 and O-4, whereas the other beta analogs carried a more reactive O-4. The same reactions were carried out using as donor the less-reactive per-O-acetylated alpha-d-galactopyranosyl trichloroacetimidate. Although the same trend was found to occur, the O-4 was always relatively more reactive with the pyranosyl donor than with the furanosyl donor, when keeping the remaining factors constant. Furthermore, the beta anomers of the acceptor gave almost exclusive substitution at O-4. These observations confirm and extend the utility of these 'matching' donor and acceptor reactivities.

Recent trends in the synthesis of O-glycosides of 2-amino-2-deoxysugars

The discovery of new methods for stereoselective glycoside synthesis and convergent oligosaccharide assembly has been critical for the area of glycosciences. At the heart of this account is the discussion of the approaches for stereoselective synthesis of glycosides of 2-amino-2-deoxysugars that have emerged during the past two decades. The introductory part provides general background information and describes the key features and challenges for the synthesis of this class of compounds. Subsequently, major approaches to the synthesis of 2-amino-2-deoxyglycosides are categorized and discussed. Each subsection elaborates on the introduction (or protection) of the amino functionality, synthesis of glycosyl donors by introduction of a suitable leaving group, and glycosidation. Wherever applicable, the deprotection of a temporary amino group substituent and the conversion onto the natural acetamido functionality is described. The conclusions part evaluates the current standing in the field and provides a perspective for future developments.

Quantum mechanics studies of cellobiose conformations

Three regions of the conformation space that describes the relative orientations of the two glucose residues of cellobiose were analyzed with quantum mechanics. A central region, in which most crystal structures are found, was covered by a 9 × 9 grid of 20° increments of the linkage torsion angles ϕ and ψ. Besides these 81 constrained minimizations, we studied two central subregions and two regions at the edges of our maps of complete ϕ,ψ space with unconstrained minimization, for a total of 85 target geometries. HF/6-31G(d) and single-point HF/6-311+G(d) calculations were used to find the lowest energies for each geometry. B3LYP/6-31G+G(d) and single point B3LYP/6-11+G(d) calculations were also used for all unconstrained minimizations. For each target, 181 starting geometries were tried (155 for the unconstrained targets). Numerous different starting geometries resulted in the lowest energies for the various target structures. The starting geometries came from five different sets that were based on molecular mechanics energies. Although all five sets contributed to the adiabatic map, use of any single set resulted in discrepancies of 3–7 kcal/mol (1 cal = 4.184 J) with the final map. For most of the targets, the starting geometry that gave the lowest energy depended on the basis set and whether the HF or B3LYP method was used. However, each of the above four calculations gave the same overall lowest energy structure that was found previously by Strati et al. This global minimum, stabilized by highly cooperative hydrogen bonds, is in a region that is essentially not populated by crystal structures. HF/6-31G(d) energy contours of the mapped central region were compatible with the observed crystal structures. Observed structures that lacked O3···O5′ hydrogen bonds were about 1 kcal/mol above the map's minimum, and observed structures that have a pseudo twofold screw axis ranged from about 0.4 to 1.0 kcal/mol. The HF/6-311+G(d) map accommodated the observed structures nearly as well.Key words: cellulose, carbohydrate, conformation, energy, flexibility, folding, helix, shape.

Solution properties of (1-->3)-alpha-D-glucan and its sulfated derivative from Poria cocos mycelia via fermentation tank

From Poria cocos mycelia yielded via a pilot scale facility-fermentation tank, a water-insoluble (1-->3)-alpha-D-glucan coded as Pi-PCM3-I was isolated by extraction with 0.5 M NaOH/0.01 M NaBH(4) aqueous solution. Nine fractions from F1 to F9 with a weight-average molecular mass (M(w)) range from 7.75 x 10(4) to 57.3 x 10(4) were prepared from the Pi-PCM3-I sample by a nonsolvent addition method. The fractions were reacted with chlorosulfonic acid-pyridine complex to product water-soluble sulfated derivatives coded as S1 to S8 with M(w) from 2.36 x 10(4) to 14.5 x 10(4) and degree of substitution (DS) of 0.86-1.38. M(w), z-average radius of gyration (s(2) (z) (1/2)), the second virial coefficient (A(2)), and the intrinsic viscosity ([eta]) of the native and sulfated Pi-PCM3-I were measured by laser light scattering (LLS), size-exclusion chromatography combined with LLS (SEC-LLS), and viscometry at 25 degrees C. The Mark-Houwink equations for Pi-PCM3-I in 0.25 M LiCl/dimethylsulfoxide (DMSO) (Me(2)SO) and for its sulfated derivative in 0.15 M NaCl aqueous solution at 25 degrees C were established to be [eta] = 1.33 x 10(-2) M(w) (0.75+/-0.01) (mL g(-1)) and [eta] = 1.46 x 10(-4) M(w) (1.13+/-0.01) (mL g(-1)), respectively. On the basis of theories for a wormlike cylinder model, the conformational parameters of the native and sulfated Pi-PCM3-I were calculated to be 760 +/- 50 and 1060 +/- 30 nm(-1) for the molar mass per unit contour length (M(L)), 6.3 +/- 0.5 and 13.1 +/- 1 nm for the persistence length (q), and 14.9 +/- 0.2 and 31.8 +/- 1 for the characteristic ratio (C( proportional, variant)), respectively. The results revealed that Pi-PCM3-I existed as an extended flexible chain in 0.25 M LiCl/Me(2)SO, and its sulfated derivative existed as a semistiff chain in 0.15 M NaCl aqueous solution. Furthermore, Pi-PCM3-I possessed similar structure and molecular parameters to wc-PCM3-I from a rotary shaker; this suggests promising industrialization of Poria cocos polysaccharides.

Stereoselective (2-naphthyl)methylation of sugar hydroxyls by the hydrogenolysis of diastereoisomeric dioxolane-type (2-naphthyl)methylene acetals

The cis axial/equatorial OH groups of methyl alpha-L- and ethyl 1-thio-alpha-L-rhamnopyranoside, 1,6-anhydro-beta-D-mannopyranose, and 1,6-anhydro-beta-D-galactopyranose were reacted with 2-naphthaldehyde dimethyl acetal to diastereomeric dioxolane-type 2,3-O-(2-naphthyl)methylene or 3,4-O-(2-naphthyl)methylene acetals. The glycosides yielded the exo- and endo-isomers in nearly 1:1 ratio, 1,6-anhydro-beta-D-mannopyranose gave predominantly the endo-, and 1,6-anhydro-beta-D-galactopyranose exclusively endo-isomer. The acetals and some of their fully protected derivatives bearing benzyl or tert-butyldimethylsilyl groups were hydrogenolised with AlH(3) (3LiAlH(4)-AlCl(3)) or with Me(3)N.BH(3)-AlCl(3) reagents. The endo-isomers were cleaved by both reagents to give axial NAP ethers, the exo-isomers of pyranosides furnished equatorial NAP ethers. However, the exo-isomers of pyranoses gave irregular axial ethers with a > 30-fold enhancement of the reaction rates with respect to the endo-isomer.

A convergent synthesis of core 2 branched sialylated and sulfated oligosaccharides

A convergent pathway for the syntheses of core 2 oligosaccharide analogues 1 and 2, and a natural form sialylated and sulfated hexasaccharide 3 was developed. Construction of pentasaccharides 24, 27 and hexasaccharide 28 was achieved by complete regioselective glycosylation of the 6-OH in the acceptors 5, 7 and 8, respectively, owing to the much higher reactivity of the primary hydroxyl group over the secondary axial hydroxyl group in these structures. Stereoselective sialylation was accomplished using donor 10 with defined configuration established through X-ray crystallographic analysis. Target oligosaccharides 1-3 were then obtained by the systematic deprotection of intermediates 24, 27 and 29. With these target oligosaccharides 1-3 obtained, biological evaluations of these molecules as enzyme substrates was undertaken and selectin binding studies are planned.

The 2-naphthylmethyl (NAP) group in carbohydrate synthesis: first total synthesis of the GlyCAM-1 oligosaccharide structures

Total syntheses of the GlyCAM-1 (glycosylation-dependent cell adhesion molecule-1) oligosaccharide structures: [alpha-NeuAc-(2 --> 3)-beta-Gal-(1 --> 4)-[alpha-Fuc-(1 --> 3)]-beta-(6-O-SO3Na)-GlcNAc-(1 --> 6)]-[alpha-NeuAc-(2 --> 3)-beta-Gal-(1 --> 3)]-alpha-GalNAc-OMe (1) and [alpha-NeuAc-(2 --> 3)-beta-Gal-(1 --> 4)-[alpha-Fuc-(1 --> 3)]-beta-GlcNAc-(1 --> 6)]-[alpha-NeuAc-(2 3)-beta-Gal-(1 --> 3)]-alpha-GalNAc-OMe (2) through a novel sialyl LewisX tetrasaccharide donor are described. Employing sequential glycosylation strategy, the starting trisaccharide was regio- and stereoselectively constructed through coupling of a disaccharide imidate with the monosaccharide acceptor phenyl-6-O-naphthylmethyl-2-deoxy-2-phthalimido-1-thio-beta-D-glucopyranoside with TMSOTf as a catalyst without affecting the SPh group. The novel sialyl Lewisx tetrasaccharide donor 3 was then obtained by alpha-L-fucosylation of trisaccharide acceptor with the 2,3,4-tri-O-benzyl-1-thio-beta-L-fucoside donor. The structure of the novel sialyl Lewisx tetrasaccharide was established by a combination of 2D DQF-COSY and 2D ROESY experiments. Target oligosaccharides 1 and 2 were eventually constructed through heptasaccharide which was obtained by regioselective assembly of advanced sialyl Lewisx tetrasaccharide donor 3 and a sialylated trisaccharide acceptor in a predictable and controlled manner. Finally, target heptasaccharides 1 and 2 were fully characterized by 2D DQF-COSY, 2D ROESY, HSQC, HMBC experiments and FAB mass spectroscopy.