Glucosides, aryl

In section H notes are appended on the preparation of specific classes of glycosides — furemosides, a-glucosides, aryl glycosides and polysaccharides. 

The use of the enzyme system then known as invertin, which was extracted from beer yeast with water and precipitated from the aqueous solution, was available to Fischer when he began his classical studies of the enzymic hydrolysis of glucosides reported in 1894. The stage was also set by another enzyme known as emulsin, which Fischer purchased from E. Merck, Darmstadt, and which was known to hydrolyze several natural aromatic glucosides such as salicin, coniferin, arbutin, and the synthetic phenyl glucoside. These aryl glucosides were already known to not be cleaved by invertin. 

Aryl glycosides of 2-amino-2-deoxy sugars, as might be expected, can be prepared by similar techniques as was illustrated by the synthesis of phenyl 3,4,6-tri-0-acetyl-2-acetamido-2-deoxy-p-D-glucoside and -D-galactoside by toluene -sulphonic acid catalysed reactions between phenol and the hexosamine penta-acetates These products were then anomerised using zinc chloride as catalyst to provide means of obtaining -anomers. 

Silver imidazolate together with mercury(II) chloride or zinc(II) chloride has proved to an efficient promoting system for glycosidations. For example, l,2-(ra/w-linked aryl glucosides have been prepared from fully acetylated glycopyranosyl bromides in almost quantitative yield (equation 6).7(5... 

Heddle and Percival48 have demonstrated that the C2- and C6-hydroxyl groups of glucosides possess acidic properties, and the instability of aryl jS-D-glucosides as compared to alkyl /J-D-glucosides is undoubtedly related to the high stability of aryloxide ions as compared to that of alkoxide ions.33... 

The question thus arises, why is the non-covalent event absolutely faster for the pyridinium salts than for the aryl glucosides A reasonable supposition is that the difference in behaviour is related to the differing ring conformations of the two sets of substrates, and if the non-covalent event... 

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