Alditol Trifluoroacetates

The use of trifluoroacetates has been particularly recommended for the separation of mono-O-methylglucitols, these esters of which are readily resolved on a column of 1% of XE-60 used in conjunction with temperature programming. In work on cellulose derivatives, the separation of 0-methylglucitols as their per (trifluoroacetates) was investigated, but it was found that, although satisfactory resolution could be obtained, quantitative relationships were not reproducible, and the ester of 2,3,4,6-tetra-O-methylglucitol is too volatile to be detected with the instrument 

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Fig. S.30. Gas chromatogram of alditol trifluoroacetates produced from a standard mixture of the parent aldoses. Peaks 1 = fucose 2 = ribose 3 = arabinose 4 = xylose 5 = mannose 6 = glucose ...

Neutral sugars were quantified by trifluoroacetic acid hydrolysis (3) and gas chormatography of alditol acetates (4). Uronic acids were determined by Blumenkrantz method... 

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. 

In model studies,224,225 oligosaccharides have been separated as their trifluoroacetates, and Vilkas and coworkers224 found that a tetra-saccharide so esterified had a retention time of six minutes at 250°. Similar results were obtained by Nakamura and Tamura,49 who showed that, on a column of OV-1 at 220°, the retention time of per-0-(trimethylsilyl)sucrose was 12 min, whereas, at 140°, the per(tri-fluoroacetate) required only 7 min. Other comparative data were provided for the common disaccharide alditols. A study of the concentration of lactose in blood was made by using this method 48 it was also shown48 that trifluoroacetylation of disaccharides proceeds more rapidly and satisfactorily in N,N-dimethylformamide than in ethyl acetate. 

A more common procedure for aldoses is their reduction with sodium borohydride to alditols and submission to GC-MS after conversion to TMS ethers [324], permethyl ethers, acetates or trifluoroacetates. This method was successfully employed in studies of the mechanism of conversion of deoxythymidine diphosphate D-glucose to deoxythymidine 4-oxo-6-deoxy-D-glucose by an oxidoreductase from E. coli [325]. An in-... 

Analysis of the monosaccharide signals in the C-NMR spectrum (103.1, 77.9, 75.0, 71.3 and 66.9) and further assignment of all proton and carbon chemical shifts using H- H COSY and HMQC experiments indicated the presence of a xylose residue. The presence of xylose was confirmed by acid hydrolysis of 44 with aqueous 2N trifluoroacetic acid followed by GC analysis of the corresponding peracetylated alditol. The D-configuration was determined by GC analysis of the l-[(S)-A-acetyl-(2-hydroxypropylamino)]-l-deoxy alditol acetate derivative as for... 

Trifluoroacetic anhydride-acetic acid, when used for the acetolysis of methylene acetals of alditols, shows the same specificity as acetic anhydride-sulfuric acid. - However, the products formed can be converted, by very mild hydrolysis, into the acetate-hydroxy derivative (6), because of facile cleavage of the (trifluoroacetoxy) methyl ether linkage (5). 

This can be illustrated by our work (O Neill et al., 1986a) on the extracellular anionic polysaccharide produced by Alcaligenes (ATCC 31555) species. The polysaccharide was hydrolyzed for 1.5 h with 0.2 M trifluoroacetic acid and the acidic oligosaccharides isolated by ion-exchange chromatography. Following reduction and methylation, the methylated oligosaccharide-alditol methyl esters were separated by reverse-phase HPLC (Fig. 9). Two major and one minor components were isolated and characterized by FAB-MS, EI-MS, and H-NMR. 

The chromatograms in Fig. 15 also show the complex product-distribution of the per(trimethylsilyl) derivatives of the formose sugars at complete conversion. Greatly simplified chromatograms result by reduction of the formose sugars to the corresponding alditols. Branched-chain alditols are resolved from the normal-chain components as their per(trimethylsilyl) derivatives. Better resolution of the normal-chain species is accomplished by using the trifluoroacetates of the polyhydric alcohols. However, there is incomplete separation of the trifiuoroacetates of the branched-chain from those of the normal-chain alditols. 

Investigations that have involved separations of trimethylsilyl ethers of alditols are listed in Table XXV (see p. 88) Tables XXVI (see p. 89), XXVII (see p. 99), and XXVIII (see p. 100) record separations based on alditol acetates, trifluoroacetates, and aldononitrile acetates, respectively. The retention times of alditol acetates have been tabulated. ... 

Trifluoroacetates have been litde used as derivatives for g.l.c. (see Part I, Section III,3 Vol. 28, p. 36), and mass spectra have thus far been recorded only for trifluoroacetylated alditols and nucleosides. ... 

Sugars are normally reduced to their alditols prior to acylation, so that each sugar gives a single derivative. Trifluoroacetates have been used for sugar alcohols in urine [127] by GC—MS and for monosaccharides [128]. 

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