Ethers of Polysaccharides

Most of the selective-etherification studies on polysaccharides have been made with cellulose, and nearly all of them have involved quantitative separation of the D-glucose derivatives formed on hydrolysis of the partially substituted celluloses. In view of their stability, ethers of polysaccharides are particularly suited to this approach. 

Investigation into the formation of carboxymethyl ethers of polysaccharides has continued, on account of the great utility of these derivatives as ion-exchange materials and polyelectrolytes. As expected, a whole series of polysaccharide derivatives of different degrees of substitution can be prepared by variation of the reaction conditions and molar proportions of monochloroacetic acid. " Published reports include the preparation of various carboxymethyl ethers of starches, amyloses, lichenan, pachymans, and chitin and introduction of the carboxymethyl group into polysaccharide derivatives constitutes a useful way of raising their solubility in water. By combining the introduction of alkyl and carboxy-... 

Cyanoethyl ethers of polysaccharides can be prepared by the reaction of alkaline polysaccharide with acrylonitrile [8,13] (reaction 7.8), and the formation of sulfoethyl ethers can be prepared by the reaction of alkaline polysaccharide with sodium vinylsulfonate [8] (reaction 7.9). 

In 1947, L-rhamnose was first recognized by Stacey as a constituent of Pneumococcus Type II specific polysaccharide. This finding was confirmed, in 1952, by Kabat et al. and in 1955 again by Stacey when 2,4- and 2,5-di-O-methyl-L-rhamnose were synthesized and the former was shown to be identical with a di-O-methylrhamnose, obtained by hydrolysis of the methylated polysaccharide. This result indicated a pyranose ring structure for the rhamnose units in the polysaccharide. Announcement of the identification of D-arabinofuranose as a constituent of a polysaccharide from M. tuberculosis aroused considerable interest. The L-enantiomer had been found extensively in polysaccharides, but reports of the natural occurrence of D-arabinose had been comparatively rare. To have available reference compounds for comparison with degradation products of polysaccharides, syntheses of derivatives (particularly methyl ethers) of both d- and L-arabinose were reported in 1947. 

D-Xylose, which is one of the most abundant sugars in plant polysaccharides, is a rare component of bacterial polysaccharides. It is found in the LPS of Type 1 Neisseria gonorrhoeae strain" GC 6. L-Xylose and its 3-methyI ether are components of the LPS of Pseudomonas maltophila strain NCTC 10257, and are j -pyranosidic. The d- and L-sugars, and different methyl ethers of these, have also been found in the LPS of some photosynthetic bacteria."... 

The first known 1-carboxyethyl ether of a sugar was 2-amino-3-0-[(/ )-l-carboxyethyl]-2-deoxy-D-glucose or muramic acid (37). It is a component of the polysaccharide moiety of the peptidoglycan in the bacterial cell-wall. It is partially replaced by the mamo isomer, 2-amino-3-6>-[(/ )-l-carboxy-ethyl]-2-deoxy-D-mannose, in the peptidoglycan from Micrococcus lyso-deikticus. 

Stevens and coworkers used their c.d. data on the various D-glucans to assign, tentatively, the bands to specific chromophores. They found that derivatives of these polysaccharides that have all of their hydroxyl groups acetylated still exhibit the 177-nm band. They assigned this band (which occurs at somewhat shorter wavelengths for the helical polymers) to the ether of the acetal chromophore. This assignment is essentially consistent with the results obtained by Johnson and coworkers on unsubstituted monosaccharides. 

Taylor H. Evans and Harold Hibbert, Bacterial Polysaccharides 203 E. L. Hirst and J. K. N. Jones, The Chemistry of Pectic Materials 235 Emma J. McDonald, The Polyfructosans and Difructose Anhydrides 253 Joseph F. Haskins, Cellulose Ethers of Industrial Significance. 279... 

The separation and identification of disaccharides is often an important step in the elucidation of the structure of a natural polysaccharide, and Percival484 has published useful data on the O-trimethyl-silyl derivatives of a variety of disaccharides and their reduction products. In some instances, the trimethylsilyl ethers of the disaccharide alditols have lower retention times than those of the disaccharide derivatives. The per-O-trimethylsilyl derivatives of gentiobi-itol and maltitol were encountered in studies on the structure of Pneumococcus Type II capsular polysaccharide.4843... 

In model experiments,205 it was found that concentration of an aqueous solution of the aldonic acids in the presence of hydrochloric acid gives exclusively the 1,4-lactones, which, on subsequent trimethyl-silylation, give only one peak on the chromatogram. This method was successfully employed for the separation of D-galacturonic, D-glucuronic, and D-mannuronic acids. Of the 1,4-lactones examined, only the trimethylsilyl ether of D-mannono-1,4-lactone was obtained in crystalline form. However, all of the derivatives showed characteristic differences in their infrared spectra in the range of 1500 to 600 cm"1. When this method was applied to the determination of uronic acids in a variety of polysaccharides,205 it was impossible to find any hydrolytic conditions under which the uronic acids were quantitatively released and then reduced, a problem experienced by other workers.20 The method was, however, successful in affording a qualitative, microscale procedure for the identification of hexuronic acids (which otherwise are difficult to detect). 

---