Alditols 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). 

Amino acid analysis of a strong acid hydrolysate (2 N HCl at 100° C for 3 h) identified only glutamic acid and this was confirmed by gas chromatography-mass spectroscopy (Fig. 4). Mild acid hydrolysis (0.5 N HCl at 80°C for 1 h) followed by direct insertion mass spectroscopy gave a spectrum identical to authentic ribose-5-phosphate (Fig. 5). Borate electrophoresis of the alditol derived from the stored material and of its acid... 

Compound A is a D-aldopentose. When treated with sodium borohydride, compound A is converted into an alditol that exhibits three signals in its C NMR spectrum. Compound A undergoes a Kiliani-Fischer synthesis to produce two aldo-hexoses, compounds B and C. Upon treatment with nitric acid, compound B yields compound D, while compound C yields compound E. Both D and E are optically active aldaric acids. 

When subjected to a Ruff degradation, a D-aldopentose, A, is converted to an aldotetrose, B. When reduced with sodium borohydride, the aldotetrose B forms an optically active alditol. The NMR spectrum of this alditol displays only two signals. The alditol obtained by direct reduction of A with sodium borohydride is not optically active. When A is used as the starting material for a Kiliani-Fischer synthesis, two diastereomeric aldohexoses, C and D, are produced. On treatment with sodium borohydride, C leads to an alditol E, and D leads to F. The NMR spectrum of E consists of three signals that of F consists of six. Propose structures for A-F. 

Fig. 9. 360 MHz iR-NMR spectrum of a mucin-type acidic pentasaccharide-alditol containing the bloodgroup-A determinant, dissolved in 2H2O, recorded at p H 7 and 25 °C.

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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