Glycosidic linkages, problems with

The relevance of the question discussed above to the problem of hydrolytic degradation of cellulose arises from both stereochemical and electronic factors associated with the difference in conformation of the glycosidic linkage as well as with the participation of the C6 oxygen in the bifurcated intramolecular hydrogen bond. The implications of these factors will now be considered. 

Combined approaches have been developed to overcome problems associated with chemically and enzymatically based methods. In such an approach, glycosidic linkages that are very difficult to introduce chemically are introduced enzymatically and vice versa. The enzymatic approach has proven to be extremely valuable for the introduction of neuramic acid units in a synthetically prepared oligosaccharide. 

In view of the purification and waste disposal problems with the chromium oxidations catalytic methods with ruthenium catalysts are more attractive. Ruthenium(Vlll) oxide is a strong oxidant that will also oxidize alkenes, alkynes, sulfides, and in some cases benzyl ethers. The method is compatible with glycosidic linkages, esters and acetals, and is usually carried out in a biphasic solvent system consisting of water and a chlorinated solvent. Acetonitrile or a phase-transfer catalyst has been shown to further promote the oxidation [29,30]. Normally, a periodate or a hypochlorite salt serve as the stoichiometric oxidant generating rutheni-um(VIII) oxide from either ruthenium(IV) oxide or ruthenium(III) chloride [30]. 

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