Acetals, of hexitols

Acetals of hexitols form preferentially according to a definite pattern elucidated by Hann and Hudson. For the methylene or benzylidene acetals they make the following generalizations. ) In the case of... 

The benzylidene or Tw-nitrobenzylidene derivatives, because of their insolubility, are well suited for isolation of small quantities of hexitols. The difficulty in obtaining completely or partially benzylidenated products free from one another limits their usefulness for characterization, since varying melting points are obtained. Cia-trans isomerization is another complication. Conversion to the acetates obviates these difficulties. 

Oxepane (seven-membered) rings (1,6-anhydrohexitols)52 have been prepared from the 3,4-isopropylidene acetals of D-mannitol, D-glucitol, and L-iditol, by way of alkaline hydrolysis of the corresponding 1,2 5,6-dianhydrides. The ring structures of the products were established through periodate oxidation and lead tetraacetate oxidation the requisite amount of formic acid was produced, and 3 equivalents of lead tetraacetate were consumed. No inversions at any of the asymmetric centers were involved in the reactions conducted, so the oxepanes had retained the configurations of the starting hexitols. 

Fig. 48.—Benzylation of the dibutylstannylene acetal of 3,4-dideoxy-D-(fireo-hexitol.-,0U04...

The analysis of hexopyranosyl-2-acetamido-2-deoxy-hexitols by g.c.-m.s. is mentioned in Chapter 22, and acetal derivatives of hexitols are referred to in Chapter 5. 

Barker, S. A., and Bourne, E. J., Acetals and Ketals of the Tetritols, Pentitols and Hexitols, VII, 137-207 Barrett, Elliott P., Trends in the Development of Granular Adsorbents for Sugar Refining, VI, 205-230 Barry, C. P., and Honeyman, John, Fructose and its Derivatives, VII, 53-98... 

The partially methylated monosaccharides obtained on depolymerization of the permethylated sample are preferably analyzed as acetates by g.l.c.-m.s., as shown by Bjomdal and coworkers.41,42 The neutral sugars and the amino sugars obtained in acetolysis-acid hydrolysis are reduced, and acetylated for the analysis, and the amino-hexitol and the neuraminic acid residues are acetylated after methanolysis. Identification with the aid of g.l.c.-m.s. has been described for all of the common components of protein- and lipid-linked glycans and oligosaccharides from animal cells, namely, the neutral sugars,41-43 hexitols,44 hexosamines,29,43,45,46 aminohexitols,31,32 and neuraminic acids.33,34,47... 

The hexitols form the typical derivatives of alcohols and glycols— esters, ethers, acetals and ketals, and metallic complexes. Because of the multiplicity of reactive groups and because of stereoisomerism, the number of theoretically possible derivatives of a given type is enormous. For example, D-mannitol on reacting with a mono reagent such as an etherifying agent or an acid, can form 35 different compounds ... 

The separation of alditols as their trifluoroacetates has been reported by Shapira227 and by Japanese authors.213-228 The latter compared the reaction of trifluoroacetic anhydride in acetonitrile, tetra-hydrofuran, or ethyl acetate.213 They found that ethyl acetate is the most satisfactory, as acetonitrile causes tailing, and tetrahydrofiiran contains an impurity, not removed by distillation, which overlaps with fueitol per(trifluoroacetate). They found that, in ethyl acetate, mannitol reacts completely in 20 minutes, in contrast to the results of Shapira, who reported that hexitols require two hours at 35° when treated with trifluoroacetic anhydride and a trace of pyridine. The Japanese workers stated that the best separations were obtained on a column of 2% XF-1105, and that other columns, such as DC-1107, SE-30, or SE-52, caused tailing and broad peaks. 

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