Fragmentation alditols

The mass spectrum of alditol acetates are easy to interpret as they fragment at each C—C bond as shown. 

Primary fragment ions from partially methylated alditol acetates (Fig. 2) arise by -cleavage with, in general, preferred formation of ... 

Fig. 2. Primary fragment ions arising by a-cleavage in the mass spectra of partially methylated alditol acetates.

Methylated alditol units in oligosaccharides are cleaved in a manner similar to that described previously for partially methylated alditol acetates. On the other hand, substituted cyclic carbohydrates undergo a variety of types of fragmentation, the most important of which are summarized in Fig. 4 for simple permethylated glycosides. 

The most easily recognizable fragment ions in the mass spectra of permethylated oligosaccharide alditols are those from nonreducing units, i.e., fragment ions at m/z 219 for permethylated hexose, m/z 189 for permethylated deoxyhexose, m/z 175 for permethylated pentose, m/z 233 for permethylated... 

The use of primary fragment ions is not enough to allow for extensive structural characterization. Careful examination, however, of the secondary fragmentation pathways provides a more precise means to identify some, but not all, of the structural characteristics for the substance under study. Aspinall (82MI7) reviewed a useful example in which the permethylated alditols from the milk oligosaccharides lacto-N-tetraose [Gai- (1 3)-Glc- l 3)-Gal-... 

Alditols are often observed as the end-products of monosaccharide metabolism that are stored in various cellular and tissue compartments with low redox potentials. However, there are also examples of alditols as important metabolic intermediates allowing the interconversion of rare forms of certain monosaccharides. In enteric bacteria such as Escherichia coli the hexitol galactitol is taken up through enzyme II of the phosphoenol pyruvate-dependent phosphotransferase system and accumulated inside the cell as galactitol 1-phosphate. The genes involved in galactitol metabolism have been cloned on a 7.8 kb DNA fragment [201]. 

Isolation of the alditol (23) on solvolysis with hydrogen fluoride of the methylated oligosaccharide fragment of P. aeruginosa L yi 0 10a O-spe-... 

PEAK NUMBER R r ALDITOL ACETATE DIAGNOSTIC PRIMARY FRAGMENT IONS ... 

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