Carbohydrates trifluoroacetyl derivatives

Vilkas and coworkers224 showed that carbohydrates can be separated as their trifluoroacetates, and included 2-amino-2-deoxy-D-glucose and deoxystreptamine in this study. Likewise, Ueno and coworkers225 were able to separate the trifluoroacetates of certain aminodeoxy-glucoses and aminodeoxycyclitols. The separation of aminodeoxy-hexitols as their trifluoroacetyl derivatives has been studied by Tamura and coworkers,563 who found a column of 2% XF-1105 the most satisfactory. 

Even isolated mono- and disaccharides are capable of extensive hydrogen bonding, which results in extremely low vapor pressures. Attempts at vaporization of these materials results in decomposition. Volatile derivatives must be prepared and the approaches are similar to those described for amino acids. The most common derivatives are methyl or trimethylsilyl ethers and acetyl or trifluoroacetyl esters. A highly detailed review of applications of GLC to carbohydrates including over 1000 references concerning derivatization and types of columns used has been written by Dutton (69,70). 

Trifluoroacetyl (TFA) derivatives, which have been used for gas chromatography of amino acids, have recently been introduced to the carbohydrate field. Vilkas et al. (317) reported the separation of a number of pentoses, hexoses, amino sugars, methyl glycosides, and disaccharides as... 

Gas liquid chromatography (GLC) has found only limited application in lichen chemistry because most lichen substances are very polar and have low volatility. To overcome this problem, more volatile derivatives are used. Nishikawa et al. (1973) analyzed the low molecular weight carbohydrates of eight lichen species as their acetyl, trifluoroacetyl and trimethylsilyl derivatives by GLC under the following conditions Hj,... 

Table 16. Relative retention times of the acetyl, trifluoroacetyl and trimethylsilyl derivates of some low molecular weight carbohydrates from lichens...

The application of enzymic methods to the structural analysis of polysaccharides has been reviewed. The second part of a review on the application of g.l.c. to carbohydrates includes details of methods of methylation, and has collected m.s. data for TMS, acetyl, trifluoroacetyl, and methyl derivatives of sugars. The high reactivity of methyl trifluoromethanesulphonate (methyl triflate) makes it a suitable reagent for methylation of carbohydrates under mild conditions. Since the high reactivity of this triflate limits the choice of solvent for the methylation, hydrophilic carbohydrates cannot normally be methylated by this procedure. 

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