Carbohydrates structural analysis, methylation techniques

The analysis of monosaccharide mixtures as the permethylated derivatives was proposed early in the application of gas-liquid chromatography to carbohydrates, but the method has now been superseded by more convenient procedures.230,231 There are, however, situations in which this method is useful, such as during a structural study of a polysaccharide by the methylation technique. The mixture of partially methylated monosaccharides obtained by methanolysis may then be fully methylated, and the proportions of the various monosaccharides determined. This approach has been used, for example, in studies on a galactomannan392 and on tamarind-kernel polysaccharide.393 Such an analysis also constitutes a useful check to ensure that no significant change in the composition of the polysaccharide occurred during methylation. 

However, two other applications of mass spectrometry to carbohydrate chemistry seem the most important and promising. These are the identification of partially methylated monosaccharides, and structural analysis of di- and oligo-saccharides (and penetration of this new technique into polysaccharide chemistry). 

Rauvala, H., Finne, J., Krusius, T., Karkkainen, J. and Jamefelt, J. (1981). Methylation Techniques in the Structural Analysis of Glycoproteins and Glycolipids . Advances in Carbohydrate Chemistry and Biochemistry, 38, 389-416. 

American Viscose was the dominant rayon company at the time and well-puriBed dissolving grade wood cellulose was constantly improved thanks to fundamental research on methods of carbohydrate analysis. Purves had originally studied at St. Andrews University where Haworth, Hirst, Purdy and Irvine pioneered the methylation techniques which were essential for chemical structure determination. 

Reviews have appeared on the use of high resolution n.m.r. spectroscopy in the structural determination of complex carbohydrates and of some 3-0-, 4-0-, and 3,4-di-O-glycopyranosyl-substituted methyl D-gtycopyranosides. The latter publication includes complete assignments of and C-n.m.r. resonances as well as conformational studies using HSEA effect theory. The application of various njnj. techniques (multi-relayed correlation, H- H-correlated, triple quantum field H- H-correlated and H- H homonuclear Hartmann Hahn spectroscopy) to carbohydrate analysis has been reviewed in Japanese, and in a further Japanese review the interactions of metal ions with uronic acids and amino sugars as observed by the lanthanide-probe n.m.r. method are discussed/... 

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. ... 

---