Alditol from monosaccharides

The more stable boron chelates can be isolated even from aqueous solution, whereas those of lower stabilities are only accessible from non-aqueous media. Catechol- and inositol-borates (3, 5 and 6) possesses a well-defined monomeric structure,75 whereas those obtained from monosaccharides and alditols are polymeric.121 A crystal structure determination122 has been carried out for sodium scyUo-inositol diborate (6). 

Paper Chromatography.— A new solvent system (nitromethane-acetic acid-ethanol-water saturated with boric acid, 8 1 1 1) that separates the common monosaccharides from each other, and that also separates alditols from each other and from their parent monosaccharides, has been reported. Paper-... 

The polyhydric alcohols arising formally from the replacement of a carbonyl group in a monosaccharide with a CHOH group are termed alditols (see 2-Carb-19). 

Although many analyses are performed on alditol acetates (see Section VII, p. 56), in order to avoid the formation of multiple peaks, such a reduction is not practical when the mixture contains ketoses, notably fructose. Such analyses are mainly encountered with medical samples and in the examination of sugars occurring free in Nature. Furthermore, the peak-area ratios may be used as a means of identification, to check on the completeness of trimethylsilylation,67,89 and, despite the complex chromatograms obtained from trimethyl-silyl derivatives, they have the merit of being rapidly formed.89 For all of these reasons, improvements in the separation of monosaccharides as their trimethylsilyl derivatives continue to be of considerable importance. 

Hydrazones 10 derived from aldose monosaccharides (9) and 2-hydrazinopyrimidine (8) gave, upon oxidative cyclization with bromine in methanol, the corresponding 3-(alditol-l-yl)-l,2,4-triazolo[4,3-a]pyrim-idines 11 [97JHC(34)1115] (Scheme 7). 

Hence, the mass spectra of alditol acetates may be used to solve problems, just as for the monosaccharide series for example, for determination of molecular weight (indirectly, from the position Of M—59 and M—73), of the position of the deoxy unit, and so forth. 

The amount of each neutral monosaccharide in the samples can be calculated relative to the internal standard, allose, using response factors. The relative response of the detector for the individual alditol acetates can be calculated from the areas under the peaks for each alditol acetate, relative to the area under the peak for allitol acetate. There should be no peaks in the chromatogram of the water control and only one peak, corresponding to allitol hexaacetate from the internal standard allose, in the chromatogram of the TFA control. 

FIGURE 5.2 The alditols derived from the C4, C5, and C6 monosaccharides in the D-series. Degenerate symmetry means that there are only three pentitols and six hexitols. 

---