Cyanogenic glycosides hydrolysis

Salicin is an (9-glycoside of a phenol, namely salicyl alcohol. Salicin is a natural antipyretic and analgesic found in willow bark, and is the template from which aspirin (acetylsalicylic acid, see Box 7.13) was developed. Prunasin from cherry laurel is an example of a cyanogenic glycoside, hydrolysis of which leads to release of toxic HCN (see Box 7.7). It is the (9-glucoside of the alcohol mandelonitrile, the trivial name for the cyanohydrin of benzaldehyde. It is the further hydrolysis of mandelonitrile that liberates HCN. 

The cyanogenic glycosides, phaseolunatin [554-35-8], C qH yNO, and vicianin [155-57-7], C2C)H25N02q, have been isolated from lima beans and vetch, respectively. Several studies have reported that heating (cooking) acts to decrease the quantity of HCN Hberated by these compounds upon enzymatic hydrolysis. 

Cyanogenic glycosides are potentially toxic because they liberate hydrogen cyanide on enzyme-catalyzed or acidic hydrolysis. Give a mechanistic explanation for this behavior for the specific cases of... 

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. 

Cyanogenic glycosides toygdalin (or its reduced form, prunasin) and dhurrin are known to be allelopathic (3,48). Not only are these glycosides hydrolyzed to produce hydrogen cyanide, but the benzaldehyde or hydroxybenzaldehyde (produced during hydrolysis) is oxidized to benzoic acid which itself nay be toxic to several species (3, 48). 

Linamurin is the principal cyanogenic glycoside in cassava its toxicity is due to hydrolysis by intestinal microflora releasing free cyanide (Padmaja and Panikkar 1989). Rabbits (Oryctolagus cuniculus) fed 1.43 mg linamurin/kg BW daily (10 mg/kg BW weekly) for 24 weeks showed effects similar to those of rabbits fed 0.3 mg KCN/kg BW weekly. Specihc effects produced by linamurin and KCN included elevated lactic acid in heart, brain, and liver reduced glycogen in liver and brain and marked depletion in brain phospholipids (Padmaja and Panikkar 1989). 

Over 2,650 plant species can produce hydrogen cyanide (Seigler 1991 Swain et al. 1992). These include edible plants such as almonds, pits from stone fruits (e.g., apricots, peaches, plums, cherries), sorghum, cassava, soybeans, spinach, lima beans, sweet potatoes, maize, millet, sugarcane, and bamboo shoots (Fiksel et al. 1981). The cyanogenic glycoside content of a foodstuff is usually expressed as the amount of cyanide released by acid hydrolysis glycoside concentrations are rarely reported (WHO 1992). 

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. 

Figure 1. 6-Glucosidase-mediated hydrolysis of cyclopentenoid cyanogenic glycosides.

Glycosides that have soaplike properties are called saponins. Similarly, glycosides that liberate hydrocyanic acid (HCN) on hydrolysis are known as cyanogenic glycosides, and glycosides that have an effect on heart muscle are called cardiac glycosides. 

Like other glycosides, cyanogenic glycosides are cleaved to a carbohydrate and an alcohol on hydrolysis. 

Ten Canadian flaxseed cultivars were analyzed for total cyanide content (Chadha, 1995) and contents of individual cyanogenic glycosides (Oomah et al., 1992). Chadha et al. (1995) determined cyanide content in 10 cultivars of flaxseed using an autohydrolysis method that required up to 5 hours of hydrolysis time. The maximum cyanide values were typically obtained... 

Cyanogenic glycosides, which are widely distributed in higher plants, are a bound form of toxic hydrogen cyanide, which is released from the glucoside following enzyme hydrolysis.214... 

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