Separation of methylated sugars

The present article is concerned with the use of gas-liquid chromatography for neutral, basic, and acidic sugars and some of their simple derivatives. A succeeding article will treat the separation of methylated sugars and their derivatives. 

Separation of methylated sugars as their methyl glycosides suffers from the disadvantage, discussed in Fart I in Sections IV (Vol. 28, p. 38) and VI (Vol. 28, p. 51), that multiple peaks are usually obtained from each component. As with the unsubstituted monosaccharides, the profile of the individual peaks, together with their retention times. 

The separation of methylated sugars by use of the derivatives discussed in Sections XVIII-XX (pp. 23-27) may in all cases, except lactones, be complicated by the formation of multiple peaks. Although the peak profile for a particular sugar can be used as a distinguishing feature, it is often more convenient to transform the sugar into a derivative that can give only a single peak. The use of lactones (see Section XX,3 p. 29) is one example this approach, but reduction to the alditol is far more common. 

Other methods have been described for the separation of methylated sugars. These include partition between an organic solvent and water 21 y 22) and separation on columns of alumina 22), silica gel 23), or charcoal 24). A micro method now generally adopted has come into being... 

Preliminary examinations of dextran structures were conducted by optical rotation, infrared spectroscopy and periodate-oxidation reactions. More detailed results can be achieved by methylation analysis [19]. The hydroxyl groups are methylated with methyl iodide after activation with sodium methylsulfinyl carbanion (Fig. 2). The methyl dextran is hydrolysed to the corresponding different methylated monosaccharides, which are furthermore reduced and peracetylated. The resulting alditol acetates of methylated sugars are separated by gas chromatography and identified by their retention times. In particular, a combined capillary gas-liquid chromatography/mass... 

Quantitative Analysis of Mixtures of Sugars by the Method of Partition Chromatography. Part IV. The Separation of the Sugars and Their Methylated Derivatives on Columns of Powdered Cellulose, L. Hough, J. K. N. Jones, and W. H. Wadman,/. Chem. Soc., (1949) 2511-2516. 

Mixtures of methylated sugars are generally fractionated by partition chromatography on cellulose columns. Lemieux and coworkers have found that columns of diatomaceous earth (for example, Celite) are as good as, or better than, cellulose columns for these separations. 

Column and paper-chromatographic methods for the separation, identification, and estimation of methylated monosaccharides have been developed, and are satisfactory, provided that the appropriate reference compounds are available. Recent developments in this field are the ready demethylation of methylated sugars with boron trichloride and the use of gas-liquid partition chromatography for the analysis of mixtures of methylated sugars. ... 

N.m.r. spectroscopy has been used to study the equilibrium between pyranoid and furanoid forms of sugars. 2,3-O-Isopropylidene-L-rhamnose was selected for careful study, since it is known that this compound exists appreciably in the furanose form. For this sugar it was not convenient to observe the anomeric proton signals in order to assess the composition of the equilibrium mixture. However it was observed that with 2,3-O-isopropylidene-L-rhamnofuranose derivatives the separation of methyl signals was 0 09-0-11 p.p.m., whereas... 

Although carbohydrates are among the most polar and non-volatile substances of biochemical interest, the use of GC in their analysis has been quite successful. They are almost a perfect example of the utility of sample derivatization. Based on the early common observations of organic chemists that methylated sugars can be distilled, the first reports on derivatization and GC of carbohydrates appeared quite early in the relevant literature. Mclnnes et al. [396] demonstrated GC of methylated sugars in 1958, while Sweeley and co-workers [184,397] introduced silylation for the same purpose. By the mid-1960 s, it was not surprising to see a GC separation of fairly large disaccharide molecules [398] such as sucrose or cellobiose. 

Another method for the separation of methylated compounds consists in converting the reducing, methylated sugar into the trimethylsilyl derivative or, less commonly, into the acetate. Multiple peaks can be formed, but, although these may complicate the chromatogram, their relative intensities and positions may aid in the identification. Alternatively, methylated sugars may be converted into their lactones. 

Hydrolysis of the methylated glucan with sulfuric acid ( ) afforded a mixture of methylated sugars which were shown hy paper chromatography ( 9) to consist of 2,3,, 6-tetra-, 2,4,6-trl-, 2,3,4-tri-, and 2,4-dl-0-methyl-D-glucose. The quantitative estimation of these methyl derivatives was carried out by separating... 

Mixtures of methylated sugars are most often encountered in the hydrol-yzates of methylated polysaccharides prepared for structural studies. Their separation is discussed in this connection in Chapter XII. 

---