Alditols permethylated, mass spectrometry

Methylation is the most widely used method to determine the position of the glycosyl linkages.Permethylation of glycolipids can be done according to the methods of Hakomori (32) and Ciucanu and Kerek (33). The permethylated derivatives are hydrolyzed and the products converted into partially methylated alditol acetates and identified by gas chromatography-mass spectrometry ( CG-MS) (34). 

Much of our knowledge on the fragmentation patterns of carbohydrate derivatives arises from studies on methylated monosaccharides, but in structural investigations, such compounds are seldom subjected to mass spectrometry. On the other hand, the molecular weight of a permethylated oligosaccharide is significantly less than that of the per(trimethylsilyl) derivative. For this reason, the mass spectra of disaccharides as -their permethylated alditols have been determined by Chizhov and coworkers, Karkkainen, and Krone and Beckey. Trisaccharides have also been studied by Karkkainen, either as permethylated glycosides or as alditols. ... 

The use of mass spectrometry in the structural analysis of carbohydrates, first reported in 1958 (114), was developed in detail by Kochetkov and Chizhov (115). They showed that, under electron impact, the acetylated and methyl ether derivatives of monosaccharides provided a wealth of structural information through analysis of typical fragmentation pathways of the initial molecular ion. This has proved of enormous utility in the structural elucidation of polysaccharides and complex oligosaccharides sequential permethylation, hydrolysis, reduction to the alditol, and acetylation, affords mixtures of peracetylated, partially methylated alditol acetates that can be separated and analyzed by use of a gas chromatograph coupled directly to a mass spectrometer (25). The mass spectra of stereoisomers are normally identical, while the gas chromatographic retention times readily permit differentiation of stereoisomers. 

F.a.b. mass spectrometry has been shown to be a useful tool for the identification of cello- and malto-ollgosaccharldes and their alditol reduction products. Permethylated slalo-oligosaccharldes liberated from parent gangllosides can be usefully examined by chemical ionization mass spectrometry with ammonia as reagent gas. Molecular weights are revealed by the MH and (M+NH ) ions and the... 

Figure 8-4. Methylation analysis of in vitro P-D-glucans. (a) Gas chromatography of the permethyl-ated alditol acetate obtained from methylation analysis of the cellulose synthesized in vitro by the enzyme from blackberry. Peak 1, derivative characteristic of (1 4) linked glucosyl units. Peak 2, internal standard (mj o-inositol). The derivative characteristic of (1 3) linked glucosyl units usually elutes 1 min before the major derivative visible in the chromatogram (not shown see Bulone et al. 1995). (b) Structural characterization by electron impact mass spectrometry of the 1,4,5-tri-0-acetyl-2,3,6-tri-0-methyl-D-glucitol derivative corresponding to peak 1 in A and characteristic of (1 4) linked glucosyl units.

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