Glycosides hydrolysis, acid-catalysed

The main cyanogenic glycoside in laurel is prunasin, the P-o-glucoside of benzaldehyde cyanohydrin. The enzymic hydrolysis of prunasin may be visualized as an acid-catalysed process, first of all hydrolysing the acetal linkage to produce glucose and the cyanohydrin. Further hydrolysis results in reversal of cyanohydrin formation, giving HCN and benzaldehyde. 

It should also be noted that hydrolysis of glycosides (acetals or ketals) will occur under acid-catalysed conditions if we have an excess of water present. This is a reversal of the process for glycoside... 

The treatment of free sugars with alcohols in the presence of acid catalysts is the procedure most commonly used to prepare simple alkyl glycosides of the type frequently used in synthetic work. Although this is one of the oldest and most widely used reactions of carbohydrates it has not, until recently, been investigated in any detail on account of the variety of competing processes involved and the complexities of the products. Alternatively, the reverse reaction, the acid catalysed hydrolysis of glycosides, which is appreciably easier to study because of the single products obtained, has been the subject of many detailed studies and is now well documented and understood. 

The hydrolysis of glycosides is achieved by specific hydrolytic enzymes, e.g. p-glucosidasc for [)-glucosides and ft-galactosidase for ft-galactosides. These enzymes mimic the readily achieved acid-catalysed processes [Figure 2.27(b)], Under acidic conditions, the a- and (Vanomcric hemiacetal forms can also equilibrate via the open chain... 

ACID-CATALYSED HYDROLYSIS OF GLYCOSIDES 3.7.1 Specific Acid Catalysis... 

Figure 3.21 Time courses of the hydrolysis of an isotopic quasi-racemate in two acid-catalysed hydrolyses of glycosides. Both figures, taken from Ref. 107, by kind permission of Prof. A. J. Bennet and the American Chemical Society, refer to a mixture of labelled d-sugar and unlabelled l-sugar (10mgmL each), show the least-squares best fit and display only every fourth data point for clarity, (a) Ring effect for methyl (3-xylopy-ranoside (b) anomeric effect for methyl 5-thio-oc-xylopyranoside. See Table 3.3 for numerical values of the effects, which are in opposite senses.

Amide participation appears to be about as effective in specific acid-catalysed hydrolysis (of the methyl glycosides) as in spontaneous hydrolysis (of the 2,4-dinitrophenyl glycosides). There is some evidence for simultaneous general acid catalysis and amide participation in the hydrolysis of p-D-GlcNAcp-OoCfiH4COOH. 

BeMiller, J.N. (1967). Acid-Catalysed Hydrolysis of Glycosides . Advances in Carbohydrate Chemistry, 22, 25-108. 

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