Sigfrid Svensson

Mass spectrometry of partially methylated alditol acetates

Abstract The mass spectra of a number of partially methylated alditol acetates, derived from methyl ethers of pentoses, hexoses, and 6-deoxyhexoses by reduction and acetylation, have been determined. Isomeric alditols having identical substitution patterns gave similar mass spectra that unambiguously determine the substitution pattern. Mass spectra should also allow determination of substitution patterns of partially methylated alditol acetates that have not previously been investigated. The method will be useful, in combination with gas-liquid chromatography, for the characterisation of different methylated sugars obtained on methylation analysis of polysaccharides.

Mass Spectrometry in Structural Analysis of Natural Carbohydrates

Publisher Summary This chapter describes that mass spectrometry (m.s.) has become an important and versatile technique in carbohydrate chemistry. The chapter deals with m.s. as a tool in the structural analysis of naturally occurring carbohydrates. The mass spectra of permethylated methyl glycosides show ions derived from a number of specific degradation pathways. These fragmentations have been carefully studied in the chapter, by using deuterium-labelling techniques. Direct derivatization of reducing sugars by permethylation, peracetylation, or per( trimethylsilyl )ation gives a mixture of glycosides. These derivatives are suitable for g.1.c. analysis, although, for complex mixtures of sugars, the multiplicity of peaks caused by the derivatization may complicate elucidation of the results. The partially methylated sugars are separated and converted into the methyl glycosides, and these are methylated with trideuteriomethyl iodide. The substitution pattern of the trideuteriomethyl groups can be determined by m.s., and the nature of the sugar ascertained by g.1.c. (by comparison with the permethylated compound used as the reference sample).

Structural studies on the O-specific side-chains of the cell-wall lipopolysaccharide from Salmonella typhimurium 395 ms

The structure of the O-specific side-chains of the cell-wall lipopolysaccharide of Salmonella typhimurium 395 MS has been investigated. Methylation analyses of the original lipopolysaccharide, of the material obtained on mild hydrolysis of the lipopolysaccharide with acid, and of a product obtained by acetalation of all of the, free hydroxyl groups in the lipopolysaccharide, followed by alkaline deacetylation, have provided the essential information in this study. The mixtures of sugars obtained on acid hydrolysis of the different methylated products were analysed, as alditol acetates, by g.l.c.-mass spectrometry. As a result of these studies, a detailed structure of the repeating unit of these side-chains is presented.

Specific Degradation of Polysaccharides

Publisher Summary This chapter discusses the chemical methods for specific or selective degradation of polysaccharides and applications of polysaccharides for structural analysis. The degradation of polysaccharides by the action of acids, followed by the fractionation and identification of the oligosaccharides formed, is one of the methods used frequently in structural polysaccharide chemistry, and it gives information both on sequences and anomeric configurations. In principle, any reaction that can be performed at the monomer level should be applicable to polysaccharides and rapid development in this field will be seen. Application of consecutive degradations, each of which should ideally be quantitative, should facilitate determination of complicated structures with moderate effort. G.l.c. an established method for the separation of the low-molecular weight products formed. Mass spectrometry and nuclear magnetic resonance spectroscopy, especially when combined with pulse Fourier transformation (PFT-n.m.r.), are becoming increasingly important for the characterization of the degradation products.

Studies on the length of the side chains of the dextran elaborated by Leuconostoc mesenteroides NRRL B-512

Abstract The length of the side chains in dextran NRRL B-512 has been studied by sequential degradation. Selective removal of the terminal d -glucosyl groups was achieved by alkaline treatment of a methylated dextran in which the hydroxymethyl groups had been replaced by C-p -tolylsulfonylmethyl groups; the 6-hydroxyl group of the new terminal units thus formed is unsubstituted. The degraded material was subjected to a second degradation by using the same procedure. The reactions were followed by methylation and/or ethylation of the products, acid hydrolysis, and analysis of the resulting mixture of ethers by g.l.c.-m.s. As a result of these studies, it is concluded that about 40% of the side chains contain only one d -glucose residue, at least 45% are two d -glucose units long, and the rest (max. 15%) are longer than two such units.

Mass spectra of partially methylated alditol acetates : Part II. Deuterium Labelling Experiments

Abstract The fragmentation pattern of some partially methylated alditol acetates on electron impact has been studied by using the technique of deuterium labelling. Detailed fragmentation mechanisms are postulated.

The structure of capsular polysaccharide of the Pneumococcus type II.

The pneumococcus type II capsular polysaccharide (SII) is composed of singly-branched hexasaccharide repeating units, for which three alternative structures have been proposed. The correct structure has now been determined by consecutive eliminations of the sugar residues in the side chain. The terminal D-glucuronic acid group was eliminated by treating the fully methylated and esterified SIIpolysaccharide first with base, and then with weak acid. The hydroxyl group at C-6 in the penultimate D-glucose residue released by this elimination was transformed into the 6-deoxy-6-tosyl derivative, and the residue thereafter eliminated by treatment with base. As the side-chains were eliminated by these reactions, it is considered that they contain only two sugar residues, which thus excludes two of the three alternative structures. Structure 1 was further confirmed by subjecting SII to a Smith degradation, which yielded the tetrasaccharide L-Rhap-(1 yields 3)-L-Rhap-(1 yields 3)-L-Rhap-(1 yields 2-erythritol, characterised by methylation analysis.

Studies of the distribution of the 4-O-methyl-d-glucuronic acid residues in birch xylan

Abstract The distribution of the 4- O -methyl- d -glucuronic acid residues in birch xylan has been studied. Elimination of the 4- O -methyl- d -glucuronic acid residues of methylated birch-xylan was followed by specific cleavage of the xylan backbone at the originally branched d -xylose residues, using a technique involving sequential oxidation, β-elimination, and mild hydrolysis with acid. The molecular weight distribution of the resulting methylated oligosaccharides indicates that the 4- O -methyl- d -glucuronic acid residues are irregularly distributed in birch xylan.

Structural studies of the o-specific side-chains of the cell-wall lipopolysaccharides from Salmonella newport and Salmonella kentucky

Abstract The structures of the O-specific side-chains of the cell-wall lipopolysaccharides (LPS) of Salmonella newport and Salmonella kentucky have been investigated. Methylation analyses of the original LPS, of the materials obtained on mild hydrolysis of the LPS with acid, and of a product obtained by acetalation of all of the free hydroxyl groups followed by deacetylation, have provided the essential information in this study. The mixtures of sugars obtained on acid hydrolysis of the different methylated products were analysed, as alditol acetates, by g.l.c.-mass spectrometry. As a result of these studies, detailed structures of the repeating units of these side-chains are presented.

Studies on the distribution of the O-acetyl groups in pine glucomannan

Abstract The distribution of the O -acetyl groups in pine glucomannan has been determined. The method used involved acetalation of the glucomannan with methyl vinyl ether, removal of the O -acetyl groups by treatment with base, and cleavage of the glycosidic linkages of the d -mannose residues carrying the original O -acetyl groups by a technique involving oxidation, β-elimination, and mild hydrolysis with acid. After removal of the acetal functions, the composition and molecular-weight distribution of the resulting oligosaccharide mixture indicated that the O -acetyl groups are irregularly distributed in the pine glucomannan.