Alditol acetates spectra

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

Analysis of the monosaccharide signals in the C-NMR spectrum (103.1, 77.9, 75.0, 71.3 and 66.9) and further assignment of all proton and carbon chemical shifts using H- H COSY and HMQC experiments indicated the presence of a xylose residue. The presence of xylose was confirmed by acid hydrolysis of 44 with aqueous 2N trifluoroacetic acid followed by GC analysis of the corresponding peracetylated alditol. The D-configuration was determined by GC analysis of the l-[(S)-A-acetyl-(2-hydroxypropylamino)]-l-deoxy alditol acetate derivative as for... 

Systematic studies on the mass spectra of alditol acetates have revealed a simple mode of fragmentation for this class of compound. Alditol acetates do not give a molecular ion, but (M — CH3CO0 ) is found in a low abundance. The mass spectra of stereoisomers are almost identical and, therefore, the mass spectrum of D-glucitol hexaacetate (see Fig. 1) is representative of all peracetylated hexitols. 

The component in peak A gave a mass spectrum identical with that of the alditol acetate of a 3,6-dideoxy-2,4-di-0-methyIhexose. As tyvelose is the only 3,6-dideoxy-hexose present, the component of the first peak must be the corresponding alditol acetate, methylated at 0-2 and 0-4. The component in peak B gave a mass spectrum characteristic of a mixture of the alditol acetates from a 6-deoxy-2,3-di-0-methylhexose (27) and a 2,3,4,6-tetra-O-methylhexose (28). 

Figure 3.19 El mass spectra of (a) peracetylated mannitol (mol wt = 434), (b) glycerol-tris-TMS (mol wt = 308), (c) 2-hydroxyethyl glucose-pentakis-TMS (mol wt = 584), and (d) partially methylated alditol acetate of 1,4-linked 2-hydroxyethylated glucose (mol wt = 394). (e) El mass spectrum of partially methylated alditol acetate of l,6-linked glucose (mol wt = 350) derived from dextran.

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