Grigory M. Lipkind

A computer-assisted structural analysis of regular polysaccharides on the basis of 13C-n.m.r. data.

A computerised approach to the structural analysis of unbranched regular polysaccharides is described, which is based on an evaluation of the 13C-n.m.r. spectra for all possible primary structures within the additive scheme starting from the chemical shifts of the 13C resonances of the constituent monosaccharides and the average values of the glycosylation effects. The analysis reveals a structure (or structures), the evaluated spectrum of which resembles most closely that observed. The approach has been verified by using a series of bacterial polysaccharides of known structure and, in combination with methylation analysis data, for the determination of the presently unknown structures of the O-specific polysaccharides from Salmonella arizonae O59 and O63, and Proteus hauseri O19.

The nuclear overhauser effect and structural factors determining the conformations of disaccharide glycosides

Abstract Conformations of (1→2)-, (1→3)-, and (1→4)-linked disaccharide methyl glycosides involving aldohexopyranose residues have been studied on the basis of the inter-unit n.O.e. and theoretical calculations using atom-atom potential functions. The preferred conformations and the n.O.e. values are determined by the absolute configurations of constituent residues, the configuration and position of the glycosidic linkage, and the orientation of the protons at the aglycon carbon associated with the glycosidic linkage and the adjacent carbons.

Conformational states of cellobiose and maltose in solution: A comparison of calculated and experimental data

Abstract A theoretical conformational analysis of the methyl β-glycosides of cellobiose and maltose was carried out and average values of the coupling constants 3 J C-1,H-4′ and 3 J C-4′,H-1 and optical linkage rotation (Λ) were calculated. It was shown that, in aqueous solutions of the disaccharide derivatives, there was a complex conformational equilibrium. The above values fitted the experimental data well if they were obtained by taking into account non-bonded interactions and torsion energy. The exo-anomeric effect and intramolecular hydrogen-bonding in aqueous solutions were shown to be of no significance.

Nuclear overhauser effects for methyl β-maltoside and the conformational states of maltose in aqueous solution

Abstract A nuclear Overhauser enhancement in methyl β-maltoside, resulting from pre-irradiation of H-1′ of the non-reducing glucose residue, has been measured and calculated theoretically. Comparison of these data reveals a complicated conformational equilibrium in aqueous solutions of maltose derivatives.

N.m.r. and conformational analysis of some 2,3-disubstituted methyl α-l-rhamnopyranosides

Abstract Conformational studies of the branched trisaccharide glycosides X-(1 → 2)[Y-(1 → 3)]-α- l -Rha-OMe (where X and Y are residues of α- l -, β- l -, α- d -, and β- d -hexopyranoses) were based on 1 H- and 13 C-n.m.r. data (n.O.e.s, 13 C chemical shifts) and theoretical calculations. In the majority of the trisaccharide glycosides, there is insignificant restriction of rotation around the glycosidic linkages in the disaccharide units as compared to the corresponding disaccharide glycosides X-(1 → 2)-α- l -Rha-OMe and Y-(1 → 3)-α- l -Rha-OMe. Differences in the conformations observed for several compounds resulted in changes of the n.O.e. patterns and in deviations from additivity of glycosylation effects in the 13 C-n.m.r. spectra.

Nuclear Overhauser effect and conformational states of cellobiose in aqueous solution

Abstract A nuclear Overhauser enhancement in α-cellobiose 1-phosphate, resulting from pre-irradiation of H-1′ of the non-reducing glucosyl group, was measured and calculated theoretically. Comparison of these data reveals a complicated conformational equilibrium in aqueous solutions of the cellobiose derivative.

The structure of the biological repeating unit of the O-antigen of Hafnia alvei O39

On mild acid-catalysed degradation of the lipopolysaccharide from Hafnia alvei O39 followed by gel filtration of Sephadex G-50, the O-specific polysaccharide and three oligosaccharides were obtained, which represent the core substituted with 0-2 O-antigen repeating-units. On the basis of sugar and methylation analyses, 13C-n.m.r. data, solvolysis of the polysaccharide with anhydrous hydrogen fluoride, and computer-assisted 13C-n.m.r. analysis of the Smith-degraded polysaccharide, it was concluded that the biological repeating unit of the O39 antigen was Formula; see text

Synthesis and 13C NMR spectra of 2,3-di-O-glycosyl derivatives of methyl α-l-rhamnopyranoside and methyl α-d-mannopyranoside

Abstract The syntheses are described of 2,3-di-O-glycosyl derivatives of methyl α- l - rhamnopyranoside (1–5)and α- d -mannopyranoside (6–9). Download : Download full-size image X Y X Y 1 α- l -Rha p α- d -Glc p 6 α- l -Rha p α- d -Glc p 2 α- d -Glc p α- l -Rha p 7 α- d -Man p α- d -Glc p 3 α- l -Rha p β- d -Glc p 8 β- l -Fuc p β- l -Fuc p 4 α- l -Rha p β- l -Fuc p 9 α- l -Fuc p β- l -Fuc p 5 β- d -Glc p β- d -Gal p The deviation from additivity in 13C NMR spectra calculated for 1–9 were similar for stereochemicallyrelated trisaccharides.

Synthesis of di-O-glycosyl derivatives of methyl α-l-rhamnopyranoside

Abstract The syntheses are described of 2,3-di-O-glycosyl derivatives (1–12) of methyl α- l -rhamnopyranoside where the glycosyl moieties are variously α- l -fucopyranose, β- l -fucopyranose, β- d -glucopyranose, α- d -mannopyranose. The syntheses involve stereoselective glycosylation of methyl 4-O-benzoyl-3-O-(2,3,4-tri-O-benzoyl-α- l -rhamnopyranosyl)-α- l -rhamnopyranoside (21), methyl 4-O-benzoyl-3-O-(2,3,4,6-tetra-O-benzoyl-α- d -mannopyranosyl)-α- l -rhamnopyranoside (25), methyl 4-O-benzoyl-O-(2,3,4,6-tetra-O-benzoyl-β- d -glucopyranoside (29), methyl 4-O-benzoyl-3-O-(2,3,4-tri-O-benzoyl-β- l -fucopyranosyl)-α- l -rhamnopyranoside (35), and methyl 4-O-benzyl-2-O-(2,3,4-tri-O-benzoyl-β- l -fucopyranosyl)-α- l -rhamnopyranoside (59). In the syntheses of compounds 7–9, the α- l -fucopyranosyl residues are introduced stereoselectively, using 2,3,4-tri-O-benzoyl-α- l -fucopyranosyl bromide (17) and ethyl 2,3,4-tri-O-acetyl-1-thio-β- l -fucopyranoside (47) as glycosyl donors.

Nuclear overhauser effects and conformations of branched trisaccharide methyl β-glycosides that contain a 2,3-disubstituted galactose residue

On the basis of the n.O.e. data and theoretical calculations, it was found that less than 90% of one conformer was present in aqueous solution for each of a series of trisaccharide methyl beta-glycosides with a 2,3-disubstituted galactose residue.