Glycosides acetals, hydrolysis

Naturally occurring compounds called cyanogenic glycosides, such as lotau-stralin, release hydrogen cyanide, HCN, when treated with aqueous acid. The reaction occurs by hydrolysis of the acetal linkage to form a cyanohydrin, which then expels HCN and gives a carbonyl compound-fa) Show the mechanism of the acetal hydrolysis and the structure of the cyanohydrin that results. 

Digestion (Section 29.1) The first stage of catabolism, in which food is broken down by hydrolysis of ester, glycoside (acetal), and peptide (amide) bonds to yield fatty acids, simple sugars, and amino acids. 

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... 

Gums are tasteless, odorless, colorless, and nontoxic. None, except the starches and starch derivatives, are broken down by human digestive enzymes. All are subject to microbiological attack. All can be depolymerized by acid- and enzyme-catalyzed hydrolysis of the glycosidic (acetal) linkages joining the monomeric (saccharide) units. 

D-Altrosan is a glycoside. The anomeric carbon—the one with two oxygen substituents—has an alkoxy group attached to it. Hydrolysis of D-altrosan follows the general mechanism for acetal hydrolysis. 

Degradation of dihydrostreptomycin in methanolic hydrogen chloride yielded methyl dihydrostreptobiosaminide, which formed a pentaacetyl derivative on acetylation. - - - Both anomers of this compound were isolated.The crystalline methyl pentaacetyldihydrostreptobio-saminfde was also obtained by selective hydrolysis of the non-glycosidic acetal group in methyl streptobiosaminide dimethyl acetal followed by catalytic hydrogenation and acetylation. 

In the first catabolic stage, digestion, food is broken down in the mouth, stomach, and small intestine by hydrolysis of ester, glycoside (acetal), and peptide (amide) bonds to jdeld primarily fatty acids, simple sugars, and amino acids. These smaller molecules are further degraded in the cytoplasm of cells to yield acetyl groups attached by a thiol ester bond (Section 21.9) to the large carrier molecule coenzyme A. The resultant compound, aceiyl coenzyme A acetyl CoA), is an intermediate in the breakdown of all main classes of food molecules. 

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 ... 

Acid catalyzes hydrolysis of the glycosidic (acetal) group. 

AC2O, FeCl3, Et20, 76-93% yield." These conditions give the acetate of the alcohol, which can then be cleaved by simple basic hydrolysis. The method is also effective for the conversion of r-butyl glycosides to acetates with retention of configuration (80-100% yield). 

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