Acetals from alditols

Having determined the rules for the formation of acetals from alditols under thermodynamic control, Dr. Mills s interest turned to the very different products obtained under kinetic control. From D-glucitol and either acetone or cyclohexanone under very mild conditions, a large number of compounds were obtained. They were not yet fully separated and characterized when ill health put the brakes on his work. 

Qualitative analysis of selected fractions was based on GLC separation of alditol acetates (5). Alditol acetates from uronosyl residues were prepared by methanolysis followed by reduction (4). 

With due consideration of the explanations just presented for the observed, relative stabilities of cyclic acetals derived from polyols, in terms of their constitution and conformation, nearly all of the following observations on the selective hydrolysis of cyclic acetals of alditols and dialkyl dithioacetals may be readily understood. 

Henry, R.J., Harris, P.J., Blakeney, A.B., and Stone, B.A. 1983. Separation of alditol acetates from plasticisers and other contaminants by capillary gas chromatography. J. Chmmatogr. 262 249-256. 

Complementary to their studies on the 0-nitrobenzylidene acetals of alditols, Tanasescu and coworkers prepared some corresponding derivatives of aldoses and examined their properties on irradiation with ultraviolet light. They found that the di-0-(o-nitrobenzylidene)aldoses are converted into 1,2-0-(o-nitrobenzylidene)-3-0-nitrosobenzoyl derivatives. In a later paper, the formation of optically inactive products from this treatment was described, but the structure of these compounds needs elaborating. These phenomena may be of greater value in effecting transformations in the carbohydrate series when more is known about them. 

Analysis of a hydrolyzate of the lipopolysaccharide from Pasteurella pseudotuberculosis Group IIA, by g.l.c. of the derived alditol acetates, revealed an unknown component. Mass spectrometry of the alditol acetate obtained after reduction with sodium borodeuteride showed a fragmentation mode compatible with the alditol acetate from a 6-deoxy-heptose. The sugar was subsequently identified as 6-deoxy-D-manno-heptose. ... 

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). 

Methanolysls of the methylated polysaccharides followed by acetylation gave a mixture of methyl glycoside acetates amongst which derivatives of 2,3-di- methylgalacturonic acid predominated (glc on column b). A further sample of the methylated polysaccharide was hydrolyzed and the derived partially methylated alditol acetates (from neutral sugar constituents only) were examined by glc-ms (Table III). A sample of fraction F2 was converted into the carboxyl-reduced... 

The formation of anhydro-derivatives from alditols under methanolysis conditions has been investigated, and xylltol, D-arabinltol, L-fucitol, D-glucltol, galactltol, 2-acet imldo-2-deoxy -D-galactltol, and the alditol of N-acetyl-neuramlnic acid were prone to anhydride formation, whereas 2-amlno-2-deoxy-D-galactitol... 

Acetylated derivatives have been used in the characterization of dialdose dianhydrides, partially methylated heptitols, and aldobiuronic acid methyl ester methyl glycosides. The origin of the fragments with even mass numbers derived from alditol acetates is based on elimination of keten, acetic acid, and acetic anhydride. ... 

Figure 8. A photograph of a GLC pattern of partially methylated alditol acetates from the trisaccharide of glucose and arabinose. 2,5-A - 1,3,4-tri-O-acetyl-2,5-di-0-methyl arabinitol 2,3,4,6-G - 1,5-di-0-acetyl-2,3,4, 6-tetra-O-methyl glucitol 2,4-A - l,3,5-tri-0-acetyl-2,4-di-0-methyl arabinitol 2,3,6-G - l,4,5-tri-0-acetyl-2,3,6-tri-0-methyl glucitol. (Reproduced with permission from Ref. 30. Copyright 1988 Academic Press.)...

A g.l.c. procedure that establishes the DP of oligo- and poly-saccharides has been developed. The oligo(poly)saccharide was reduced prior to hydrolysis and conversion of the reducing sugars liberated into their oxime derivatives the DP was determined from the ratio of acetylated aldononitrile to acetylated alditol. A similar technique, which determined the ratio of aldose acetate to alditol acetate, was used to measure the DP of amylose. ... 

Anumula, K.A., and Taylor, P.B. (1992) A comprehensive procedure for preparation of partially methylated alditol acetates from glycoprotein carbohydrates. Analytical Biochemistry, 203,101-108. 

Oligosaccharides were isolated from PMII by weak acid hydrolysis and separation by SEC and HPAEC-PAD. The isolated oligosaccharides were desalted, reduced and methylated. GC-MS analysis of the partially methylated alditol acetates has been used to reveal the structure of the oligosaccharides. 

Multiple-ion monitoring is, however, of considerable value in structural studies, but only if model compounds of known structure are available for comparison. Such an approach has been used in the study of the carbohydrate structures of glycoproteins from different tissues.50 Separation of glycopeptides obtained from various tissues was performed on columns of concanavalin A-Sepharose. Structural analysis by multiple-ion monitoring of partially methylated, alditol acetates derived from the various fractions indicated that the glycopeptides were separated according to the linkage pattern of mannose (see Fig. 1). 

Fig. 1.—Mass Fragmentograms of Partially Methylated Alditol Acetates Obtained from Rat-brain Glycopeptides. [(A) Fraction A glycopeptides, (B) fraction B glycopep-tides, and (C) fraction C glycopeptides. Peak 1, 2,3,4-tri-O-methylfucitol peak 2,...

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. 

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