Linkage analysis Hakomori methylation

Hakomori methylation analysis, and preparation and GLC gf the PAAN derivatives (4), were used to determine the linkages. C NMR of partially hydrolysed samples confirmed the octasaccharide repeat unit, the beta linkages and the presence of the carboxylic acids. 

Substitution reactions at secondary hydroxyls are generally performed either for analysis of structure or to serve a protective function during other reactions. Etherification of the nonanomeric hydroxyls was an important structural tool in the analysis of oligosaccharide and polysaccharide structure. Methyl ethers have been employed for structural determination for more than 75 years. Thus, methyl ether formation in a polysaccharide results in substitution only at free hydroxyls. Subsequent analysis of the methylated derivatives reveals positions previously occupied in glycosidic linkage. Reagents used for this purpose have evolved from dimethylsulfate to the commonly employed method of Hakomori using sodium hydride and dimethylsulfoxide. 

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