Glycosides alkali-lability

Kuhn and Low149 (see also, Ref. 150) were the first to recognize that glycosidic linkages that are) to a carbonyl group are alkali-labile, and are... 

Obviously, these methods are inapplicable to esterification of free sugars and of alkali-labile glycosides and esters (including the resultant sulfonic esters), but may be employed with sugar alcohols, non-reducing di- and oligo-saccharides, and alkali-stable glycosides and acetals (e.g., certain-O-isopropylidene derivatives). 

The mechanism proposed by Evans is reasonable and attractive however, it is based largely on indirect evidence and on thp assumption that the glycosidic enediol linkage is alkali-labile. The evidence cited to support this latter assumption must be reviewed in the light of present understanding of the mechanisms by which these substances are degraded by... 

Glycosides are generally considered to be stable toward alkali, although several types of alkali-labile glycosides are known.161 Recently, however, the alkaline hydrolysis of glycosides that are stable under normal conditions has been demonstrated to occur under drastic conditions.162 This type... 

Kenyon and coworkers found that celluronic acids are degraded in alkaline solution to generate acidity, and suggested that this alkali-lability is due to the presence of small proportions of ketonic groups in these products. They postulated that the ketone groups enolize in alkali, the enediols then split, and adjacent glycosidic links hydrolyze in such a way as to initiate an extensive alkaline degradation. 

Figure 1.1 Beta-elimination at a residue of galacturonic acid methyl ester in a pectin. The reaction will not occur if the carboxyl group is free. Breakage of the glycosidic bond occurs under alkaline conditions and both fragments can be labelled with tritiated borohydride. Similar reactions occur with alkali-labile glycopeptides.

The internucleotide bonds are susceptible to hydrolysis. Also, the glycosidic bond between the furanose and the base is acid labile, especially with the purine nucleotides. Further, the presence of the 2 -hydroxyl group in ribonucleic acids renders the RNAs alkali labile. 

An early example of the alkaline degradation of an enol glycoside is that of theobromine j3-D-glucopyranoside tetraacetate, discovered by Fischer and Helferich 70). The alkali lability of glycosides with enols of the type... 

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