pH Dependent Thermal Stabilization of DNA by Glcβ(1→3)GlcNAcβ1→STol

A disaccharide, Glcβ(1→3)GlcNAcβ1→STol (GGS, 1 ), was synthesized and demonstrated to stabilize ct‐DNA during the denaturing process. GGS at 50 μM shifted T_m of ct‐DNA by 23 °C and the behavior was pH dependent. Poly(dA‐dT)₂ was found to be the preferable type of DNA for GGS stabilization by circular dichroism spectroscopy study.     

具有β-(1→6)-半乳吡喃糖骨架和α-L-(1→3)-阿拉伯呋喃糖侧链的阿拉伯半乳寡糖的简易合成

4-Methoxyphenyl glycoside of β-D-Galp-(1→6)-[α-L-Araf-(1→3)-]β-D-Galp-(1→6)-β-D-Galp-(1→6)-{β-D-Galp-(1→6)-[α-L-Araf-(1→3)-]β-D-Galp-(1→6)-β-D-Galp-(1→6)-}2β-D-Galp-(1→6)-[α-L-Araf-(1→)3)-]β-D-Galp-(1→)6)-β-D-Galp was synthesized with 2,3,4,6-tetra-O-benzoyl-α-D-galactopyranosyl trichloroacetimidate (1), 6-O-acetyl-2,3,4-tri-O-benzoyl-α-D-galactopyranosyl trichloroacetimidate (11), 4-methoxyphenyl 3-O-allyl-2,4-tri-O-benzoyl-β-D-galactopyranoside (2),isopropyl 3-O-allyl-2,4-tri-O-benzoyl--thio-β-D-galactopyranoside (12),4-methoxyphenyl 2,3,4-tri-O-benzoyl-β-D-galactopyranoside (5), and 2,3,5-tri-O-benzoyl-α-L-arabinofuranosyl trichloroacetimidate (8) as the key synthons.     

Highly Efficient Regio- and Stereoselective Synthesis of β-（1 →6）-Branched β-（1 →3）-Linked Glucohexaose and Its Analogue

A β-（1→）6）-branched β-（1→）3）-linked glucohexaose （1） and its lauryl glycoside （2）, present in many biologically active polysaccharides from traditional herbal medicines such as Ganoderma lucidum, Schizophyllum commune and Lentinus edodes, were highly efficiently synthesized. Coupling of 2,3,4,6-tetra-O-benzoyl-β-D-glucopyranosyl- （1--）3）-2-O-benzoyl-4,6-O-benzylidene-a-D-glucopyranosyl trichloroacetimidate （7） with 3,6-branched acceptors 8 and 12 gave β-（1→）3）-linked pentasaccharides （9） and （13）, then via simple chemical transformation 4＇,6＇-OH pentasaccharide acceptors 10 and 14 were obtained. Regio- and stereoselective coupling of 3 with 10 and 14 gave β-（1→）3）-linked hexasaccharides （11） and （15） as the major products. Deprotection of 11 and 15 provided the target sugar 1 and 2. Thus, a new method for the preparation of this kind of compounds was developed.     

Regioselective Lactonization of α‐(2→8)‐Trisialic Acid

A simple and selective method has been developed to obtain both monolactones of the title compound, a model compound for biologically important polyneuraminic acid derivatives: acidic lactonization and alkaline hydrolysis of dilactone 1 . The two monolactonized trimers can be separated by capillary electrophoresis, and then distinguished by enzymatic hydrolysis with neuraminidase; only the 2‐monolactone undergoes reaction.     

Synthesis of β-（ 1→6）-Branched （ 1→3）-Glucononaoside with Alter-nate β- and α-Bonds in the Backbone

Lauryl glycoside of β-D-Glcp-(1→3)-[β-D-Glcp-(1→6)-]α-D-Glcp-(1→3)-β-D-Glcp-(1→3)-[β-D-Glcp-(1→6)-]α-D-Glcp-(1→3)-β-D-Glcp-(1→3)-[β-D-Glcp-(1→6)-]β-D-Glcp was synthesized through 3 3 3 strategy. 3-O-Allyl-2,4,6-tri-O-benzoyl-β-D-glucopyranosyl-(1→3)- -[2, 3, 4, 6-tetra-O-benzoyl-β-D-glucopyranosyl-(1→6)-] 1,2-O-isopropylidene-α-D-glucofuranose was used as the key intermediate which was converted to the corresponding trisaccharide donor and acceptor readily.     

Derivatization of sialic acids for stabilization in matrix‐assisted laser desorption/ionization mass spectrometry and concomitant differentiation of α(2 → 3)‐ and α(2 → 6)‐isomers

Sialylated carbohydrates usually decompose by loss of sialic acid when ionized by matrix‐assisted laser desorption/ionization (MALDI) as the result of the labile carboxylic proton. Stabilization has previously been achieved by forming methyl esters with methyl iodide, a procedure that eliminates the labile proton. In this paper, we describe an alternative procedure for methyl ester formation that provides information on the sialic acid linkage directly from the MALDI spectrum. The sugars were desalted, dissolved in methanol, and treated with 4‐(4,6‐dimethoxy‐1,3,5‐triazin‐2‐yl)‐4‐methylmorpholinium chloride (DMT‐MM). After removal of the solvent, the products were transferred directly to the MALDI target and examined from 2,5‐dihydroxybenzoic acid. Small amounts of N‐glycans derived from biological sources benefited from an additional clean‐up stage involving Nafion 117. α(2 → 6)‐Linked sialic acid produced only methyl esters whereas α(2 → 3)‐linked sialic acids were converted into their lactones providing a 32 Da difference in mass. Negative ion collision‐induced decomposition (CID) mass spectra of these neutralized glycans provided information, in many cases, on the antenna of N‐linked glycans to which the variously linked sialic acids were attached. The method was applied to N‐linked glycans released from bovine fetuin and porcine thyroglobulin. Copyright © 2008 John Wiley & Sons, Ltd.     

Methyl β‐d‐galactopyranosyl‐(1→4)‐β‐d‐allopyranoside tetrahydrate

The title compound, C₁₃H₂₄O₁₁·4H₂O, (I), crystallized from water, has an internal glycosidic linkage conformation having ϕ′ (O5_Gal—C1_Gal—O1_Gal—C4_All) = −96.40 (12)° and ψ′ (C1_Gal—O1_Gal—C4_All—C5_All) = −160.93 (10)°, where ring‐atom numbering conforms to the convention in which C1 denotes the anomeric C atom, C5 the ring atom bearing the exocyclic hydroxymethyl group, and C6 the exocyclic hydroxymethyl (CH₂OH) C atom in the βGalp and βAllp residues. Internal linkage conformations in the crystal structures of the structurally related disaccharides methyl β‐lactoside [methyl β‐d ‐galactopyranosyl‐(1→4)‐β‐d ‐glucopyranoside] methanol solvate [Stenutz, Shang & Serianni (1999). Acta Cryst. C 55 , 1719–1721], (II), and methyl β‐cellobioside [methyl β‐d ‐glucopyranosyl‐(1→4)‐β‐d ‐glucopyranoside] methanol solvate [Ham & Williams (1970). Acta Cryst. B 26 , 1373–1383], (III), are characterized by ϕ′ = −88.4 (2)° and ψ′ = −161.3 (2)°, and ϕ′ = −91.1° and ψ′ = −160.7°, respectively. Inter‐residue hydrogen bonding is observed between O3_Glc and O5_Gal/Glc in the crystal structures of (II) and (III), suggesting a role in determining their preferred linkage conformations. An analogous inter‐residue hydrogen bond does not exist in (I) due to the axial orientation of O3_All, yet its internal linkage conformation is very similar to those of (II) and (III).     

Synthesis of propyl O-(α-L-rhamnopyranosyl)-(1→3)-[2,4-di-O-(2s-methylbutyryl)-α-L-rhamnopyranosyl]-(1→2)=(3-O-acetyl-β-D-glucopyranosyl)-(1→2)-βp-D-fucopyranoside,the tetrasaccharide moiety of Tricolorin A

Propyl O-(α-L-rhamnopyranosyl)-(1→3)-[2,4di-O-(2s-methylbutyryl)-α-L-rhamnopyranosyl]-(1→2)-(3-O-acetyl-β-glucopyranosyl)-(1→2)-β-D-fucopyranoside (1), the tetrasaccharide moiety of Ricolorin A, was synthesized in total 23 steps with a longest linear sequence of 10 steps, and overall yield of 3.7% from D-Glucose. The isomerization of the dioxolane-type benzylidene in the prance of NIS/AgOTf was observed. Tetrasaccharide 1 exhibited no activity against the cultured P388 cell as Tricolorin A did.     

Methyl β‐allolactoside [methyl β‐d‐galactopyranosyl‐(1→6)‐β‐d‐glucopyranoside] monohydrate

Methyl β‐allolactoside [methyl β‐d ‐galactopyranosyl‐(1→6)‐β‐d ‐glucopyranoside], (II), was crystallized from water as a monohydrate, C₁₃H₂₄O₁₁·H₂O. The βGalp and βGlcp residues in (II) assume distorted ⁴C₁ chair conformations, with the former more distorted than the latter. Linkage conformation is characterized by ϕ′ (C2_Gal—C1_Gal—O1_Gal—C6_Glc), ψ′ (C1_Gal—O1_Gal—C6_Glc—C5_Glc) and ω (C4_Glc—C5_Glc—C6_Glc—O1_Gal) torsion angles of 172.9 (2), −117.9 (3) and −176.2 (2)°, respectively. The ψ′ and ω values differ significantly from those found in the crystal structure of β‐gentiobiose, (III) [Rohrer et al. (1980). Acta Cryst. B 36 , 650–654]. Structural comparisons of (II) with related disaccharides bound to a mutant β‐galactosidase reveal significant differences in hydroxymethyl conformation and in the degree of ring distortion of the βGlcp residue. Structural comparisons of (II) with a DFT‐optimized structure, (II_C), suggest a link between hydrogen bonding, pyranosyl ring deformation and linkage conformation.     

Disorder and conformational analysis of methyl β‐d‐galactopyranosyl‐(1→4)‐β‐d‐xylopyranoside

Methyl β‐d ‐galactopyranosyl‐(1→4)‐β‐d ‐xylopyranoside, C₁₂H₂₂O₁₀, (II), crystallizes as colorless needles from water with positional disorder in the xylopyranosyl (Xyl) ring and no water molecules in the unit cell. The internal glycosidic linkage conformation in (II) is characterized by a ϕ′ torsion angle (C2′_Gal—C1′_Gal—O1′_Gal—C4_Xyl) of 156.4 (5)° and a ψ′ torsion angle (C1′_Gal—O1′_Gal—C4_Xyl—C3_Xyl) of 94.0 (11)°, where the ring atom numbering conforms to the convention in which C1 denotes the anomeric C atom, and C5 and C6 denote the hydroxymethyl (–CH₂OH) C atoms in the β‐Xyl and β‐Gal residues, respectively. By comparison, the internal linkage conformation in the crystal structure of the structurally related disaccharide, methyl β‐lactoside [methyl β‐d ‐galactopyranosyl‐(1→4)‐β‐d ‐glucopyranoside], (III) [Stenutz, Shang & Serianni (1999). Acta Cryst. C 55 , 1719–1721], is characterized by ϕ′ = 153.8 (2)° and ψ′ = 78.4 (2)°. A comparison of β‐(1→4)‐linked disaccharides shows considerable variability in both ϕ′ and ψ′, with the range in the latter (∼38°) greater than that in the former (∼28°). Inter‐residue hydrogen bonding is observed between atoms O3_Xyl and O5′_Gal in the crystal structure of (II), analogous to the inter‐residue hydrogen bond detected between atoms O3_Glc and O5′_Gal in (III). The exocyclic hydroxymethyl conformations in the Gal residues of (II) and (III) are identical (gauche–trans conformer).     

Conformational studies of the β(1→3) linked disaccharide component of the immunologically active pentasaccharide of the Forssman antigen

Conformational energy calculations at the PCILO level of approximation were performed on β(1 → 3) linked disaccharide consisting of N-acetylgalactosamine and galactose of the Forssman antigen to examine the side group conformations and their influence on the mutual orientations of the two pyranosyl rings. Two low energy regions for the glycosidic bond conformation have been located in the grid search using classical potential functions. The PCILO energy minimizations were then carried out in each of these regions. The preferred orientations of the nonreducing pyranosyl ring relative to the reducing ring were found to be in agreement with the available x-ray results. Moreover, the orientations of groups attached to the anomeric carbons were in good accordance with the requirements of the exo-anomeric effect.     

Oligosaccharides Related to Tumor-Associate Antigens. Part 2. Conformational analysis of the trisaccharide α-L-Fucp-(1→2)-β-D-Galp-(1→3)-β-D-GalpNAc,epitope structure recognized by the MBr1 antibody

The conformational space of the trisaccharide α-L -Fuc-(1→2)-β- D -Gal-(1→3)-β -D -GalNAc-1-OPr ( 2 ) and of its component disaccharide moieties α -L -Fuc-(1→2)-β -D -Gal-1-OMe ( 3 ) and β -D -Gal-(1→3)-β- D -GalNAc-1-OPr ( 4 ) was investigated with the aid of molecular-mechanics energy minimizations and molecular-dynamics simulations. These calculations suggested the occurrence of two conformations for each compound characterized by different ? and Ψ glycosidic angles. However, ¹H-NMR investigation of D₂O solutions of 2–4 indicated a sure preference for one of the two conformers with a contribution of the other one ranging from negligible to low.     

Ceric-ion-initiated grafting of methyl methacrylate onto (1 → 5)-α-D-ribofuranan and (1 → 5)-α-D-xylofuranan

We report herein studies of grafting of MMA onto (1 → 5)-α-D -ribofuranan and (1 → 5)-α-D -xylofuranan by ceric ion initiation both in water and in dimethyl sulfoxide (DMSO). In aqueous medium, the graft polymer having high grafting (%) can be obtained easily without adding any nitric acid. The degradation of polysaccharide by the acidic ceric ion solution is not serious; 73–82% of its original molecular weight remained after the polymerization. In DMSO, graft polymers having lower grafting (%) and lower molecular weight of grafts were obtained.