Acetylated alditol acetates, preparation 7-Acetylation

The preferred method for reduction and acetylation is that of Blakeney et al. (1983). Their innovation was to use DMSO as the solvent for sodium borohydride and to use 1-methylimidazole as the catalyst for the quantitative acetylation of alditols in the presence of borate. Methods commonly used to prepare alditol acetates prior to this had incorporated steps in which the borate was removed by repeated evaporations with methanol, which was slow and tedious. 

In the methylation analysis [69-72], an LCC preparation is methylated with CH3I in DMSO under strong alkaline conditions. The resulting methylated LCC sample is then subjected to acid-catalyzed hydrolysis to obtain partially methylated sugar monomers. The hydrolysate is then reduced and acetylated and the resulting alditol acetate mixture is analyzed by GC and GC-MS. The nature of the carbohydrate bonding sites is then elucidated from the umnethylated (acetylated) sites of the monomeric saccharides which are identified and quantified (Fig. 4). 

The substitution of sodium acetate or N-methyl-imldazole for pyridine in the preparation of alditol acetate derivatives for the capillary g.c. analysis of neutral and amino-sugars using selected ion monitoring m.s. detection has been examined. While N-methyl-imidazole effected full acetylation of alditols in the presence of borates and water, it led to a higher detector background than the more tedious use of sodium acetate. Muramic acid produced two alditol acetate derivatives, the lactams (1) and (2), in a reproduceable fashion only in the sodium acetate-catalyzed procedure... 

Mixtures containing nearly all possible partially methylated alditol acetates have been prepared as standards for the methylation analysis of cell-wall polysaccharides. Incomplete Hakamori methylation (1.e. limiting amounts of potassium dimsyl) of neutral monosaccharides with purification of the derivatives on a C g reversed-phase column was followed by standard hydrolysis, reduction, and acetylation. Relative capillary g.c. retention data was... 

Improved procedures for the preparation and g.c. analysis of peracetylated aldoses have been developed. Acetylation (AcjO-l-raethylimidazole) can be performed directly on acid hydrolysates, and factors influencing the ratios of isomers produced have been studied. This method was compared with the alditol acetate procedure for the quantitative analysis of four plant materials. G.l.c.-m.s. data have been reported for partially methylated and acetylated derivatives of L-gfycero-n-manno- and n-gfycero-D-manno-heptoses and -heptitols. ... 

A new method for preparing alditol acetate derivatives has been detailed which avoids the need to remove borate prior to acetylation,... 

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