Mass spectrometry polysaccharide structure determination

Lupescu, N., Solo-Kwan, J., Christiaen, D., Morvan, H., and Arad, S. M. (1992). Structural determination by means of gas chromatography-mass spectrometry of 3-0-(a-D-gluco-pyranosyluronic acid)-galactopyranose, an aldobiuronic acid derived from Porphyridium sp. polysaccharide. Carbohydr. Polym. 19 131-134. 

Equally important as NMR spectroscopy is the development of mass spectrometry where advances have been even more spectacular, partly due to its far greater sensitivity. A broad introduction is provided by Hocart (Chapter 9.10), who describes the range of available spectrometers and techniques. In the next chapter (Chapter 9.11), Dorrestein and his coauthors describe applications to the elucidation of biosynthetic pathways, focusing on nonribosomal peptides and polyketides, while Das provides a detailed account of the structure determination of proteins and peptides in Chapter 9.12. In yet another illustration of the power of mass spectrometry to analyze biomacromolecules, Li and Altman extend the technique to a study of bacterial polysaccharides (Chapter 9.13). 

The Introduction to this article (see p. 10) drew attention to the advances in the determination of polysaccharide structures that have accrued as a result of the combination of three techniques. Two of these, namely, methylation, and g.l.c. separations of the metbylated sugars thus obtained, have been treated in previous Sections. It remains, therefore, to indicate the impact of mass spectrometry (m.s.) on certain aspects of the chemistry of polysaccharides. 

Much of the earlier work on the mass spectrometry of carbohydrates was discussed in this Series by Kochetkov and Chizhov, and the same authors have presented certain practical aspects of the technique. Hanessian described the application of mass spectrometry to natural products containing sugars, and other reviews have been written by Rosenthal and Heyns and coworkers. Lindberg and coworkers discussed the combined use of gas-liquid chromatography and mass spectrometry (g.l.c.-m.s.) with reference to alditol acetates and, elsewhere in this Series (see Vol. 29, Chapter 3), Ldnngren and Svensson amplified this topic. The purpose of the present Section is to collate those literature reports relevant to the determination of polysaccharide structures, but not to discuss such matters as the mechanism by which the fragments are formed, information on which can be found in the reviews and articles mentioned. 

The chemical structure of lipid A of lipopolysaccharide isolated from Comamonas testosteroni was recently determined by lida et al. (1996) by means of methylation analysis, mass spectrometry and NMR. The lipid A backbone was found to consist of 6-0-(2-deoxy-2-amino-P-D-glucopyrano-syl)-2-deoxy-2-amino-alpha-D-glucose which was phosphorylated in positions 1 and 4. Hydroxyl groups at positions 4 and 6 were unsubstituted, and position 6 of the reducing terminal residue was identified as the attachment site of the polysaccharide group. Fatty acid distribution analysis and ES/MS of lipid A showed that positions 2,2, 3 and 3 of the sugar backbone were N-acylated or O-acylated by R-3-hydroxydecanoic acid and that the hydroxyl groups of the amide-linked residues attached to positions 2 and 2 were further O-acylated by tetradecanoic and dodecanoic acids, respectively. 

Although beyond the scope of this chapter, it is worth remembering that El has enjoyed considerable success in the analysis of small carbohydrates, particularly monosaccharides, and is still valuable as the ionization method in combined gas chromatography/mass spectrometry (GC/MS) systems for the determination of composition and linkage. Methylation analysis whereby polysaccharides are permethylated, hydrolyzed and then further acetylated is still a valuable technique for structural investigation and should not be discarded in the light of the more recently developed techniques such as ESI and MALDI. Methods for permethylation of carbohydrates have recently been reviewed. ... 

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