Hydrolysis of a Glycoside

This type of reaction was used by Langenbeck24 to describe the mechanism underlying the enzymatic hydrolysis of a glycoside (Fig. 4). This... 

Figure 16. Acid-catalyzed hydrolysis of a glycosidic linkage...

The alcohol or phenol formed from hydrolysis of a glycoside is called an aglycon. What monosaccharide and aglycon are formed by acidic hydroiysis of indican, the giycoside precursor of the biue pigment indigo ... 

Aglycon (Section 27.7C) The alcohol formed from hydrolysis of a glycoside. 

Benzylidene acetals, very fragile in an acidic medium, are hydrolysed by aqueous acetic acid or cleaved by hydrogenolysis. Selectivity can be observed in the hydrolysis of isopropylidene acetals. With compound 5.10, only the ring spanning positions 5 and 6 is hydrolysed by aqueous acetic acid. Hydrolysis of the acetal function which involves the anomeric oxygen requires heating in mineral acid (0.1 M) for a few hours, comparable conditions to those of hydrolysis of a glycoside. 

Many plants owe their activity to compounds which are only formed as a result of post harvest enzyme effects. Examples include vanilla pods where there is no vanillin in the freshly picked pod it is formed only during fermentation of the pod which involves an enzymatic hydrolysis of a glycoside. 

The initial step of the acid-catalyzed hydrolysis of a glycoside, as well as of any acetal or ketal, is a fast and reversible protonation of one of the two acetal oxygens of a sugar glycoside (Fig. 3.1). 

Glycosides are stable in basic solutions because they are acetals. In acidic solutions, however, glycosides undergo hydrolysis to produce a sugar and an alcohol (again, because they are acetals. Section 16.7B). The alcohol obtained by hydrolysis of a glycoside is known as an aglycone ... 

Aglycone (Section 22.4) The alcohol obtained by hydrolysis of a glycoside. 

Formation of a Glycoside 988 Hydrolysis of a Glycoside 989 Phenylosazone Formation 1000... 

D-Xylosyl-D-glucose (primeverose). M.p. 209°C. [o ]d +23° —> —3.4° (water) obtained by partial hydrolysis of a glycoside from Primula officinalis 132) from madder root 133). (See Ruberythric acid.) The synthesis has been accomplished by coupling 2,3,4-tri-O-acetyl-a-D-xylosyl bromide with 1,2,3,4-tetra-O-acetyl-iS-D-glucose 134). 

Glycosidase-catalyzed hydrolysis of a glycoside bond in a polysaccharide can occur with either inversion or retention of stereochemistry at the anomeric center. Both mechanisms probably proceed through a short-lived oxonium ion (RaO" ") intermediate in which one face of the carbohydrate is effectively shielded by the leaving group, leaving the other face open to nucleophilic... 

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