Glycoside cyanogenic

Cyanogenic glycosides (Table 16.22) are present in lima beans and in some other plant foods. Precursors of cyanogenic glycosides are the amino acids listed in Table 16.22. As in the biosynthesis of glucosinolates (cf. 17.1.2.6.5), an aldoxime is initially formed, which is then transformed into 

The substrate specificity of P-glucosidase is governed by an aglycon moiety. Thus, the enzymes present in emulsin , a glycosidase mixture from bitter almonds, hydrolyze not only amygdalin but also other cyanogenic glycosides which are de- 

Glycoside Name Structure Sugar Amino acid precursor Occurrence (seeds) 

Linamaiin CH3 CH3 Glucose Val Lima bean Linseed (flax) Cassava 

As shown in Fig. 16.4, P-glucosidase hydrolysis produces an unstable hydroxynitrile which slowly degrades into the corresponding carbonyl compound and HCN. However, most legume seeds contain a hydroxynitrile lyase which accelerates this reaction. 

Krt L L L JUM 2 1 1 H H L-Amino acid 2, 2 0-Sugar Cyanogenic Glycoside 1 R2 Sugar Configuration at C-2 

Cyanogenic glycosides are formed in higher plants and some insects, e.g., Zygaena and Heliconius species. About 25 representatives are known today. 

Cyanogenic glycosides are formed from L-amino acids (Table 43). An enzyme complex comprising enzymes 1-4 yields an oc-hydroxynitrile (A 3.1) which is glucosylated in the last step. An important reaction in the biosynthesis of tri-glochinin is the oxidative splitting of the aromatic ring of L-tyrosine. 

1 L-Amino acid iV-monooxygenase 2 iV-hydroxy amino acid dehydrogenase (oxydative decarbo-xylating) 3 aldoxime dehydratase 4 nitrile monooxygenase 5 glucosyltransferase 

Cyanogenic glycosides act as feeding deterrents in plants and animals (E 5.5.3) and in the protection of plants to microbial attack (E 5.4). The HCN liberated during destruction is toxic to grazing animals or plant pathogens due to the interaction with enzyme systems containing heavy metal ions, e.g., cytochromes. 

The deviating metabolism of i -amino-acids in plants clearly calls for caution in the indiscriminate use of racemic amino-acid precursors in biosynthetic experiments. 

Another uniform group of naturally occurring cyanogenic compounds, the cyanolipids, which are limited in distribution, with one exception, to seed oils of members of the family Sapindaceae, has only recently been structurally clarified. Collectively, they are esters, divisible, according to their alcohol moieties, into four obviously related groups of undecided steric compositions, (57)—(60). Striking, and repeatedly commented upon, is the 

In a full account of preliminarily published results, detailed evidence is presented for the above conclusions, reached through experiments with linen flax seedlings, producing linamarin (62 R = R = Me), and cherry laurel or peach shoots, synthesizing prunasin (62 R = H, R = Ph). A notable incorporation of 2-oximinoisovaIeric acid and 2-oximino-3-phenylpropionic acid into linamarin and prunasin, respectively, may conceivably reflect the role of the oximino-acids as sources of nitriles, formed by a long-known, non-enzymic conversion. Experiments aimed at inducing accumulation of intermediates 

Tyrosine, but not phenylalanine or Dopa, serves as the amino-acid precursor in plant-feeding experiments. The possibility of the oxidative ring cleavage being associated with the release of hydrocyanic acid in the catabolism of tyrosine-derived glucosides in higher plants has been discussed.  

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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. 

Nonvolatile Inhibitors. Glycosides A number of toxic constituents are known to be released by the enzymatic degradation of various glycosides. Some of the volatile components have been mentioned previously—i.e., isothiocyanates from mustard oil glycosides and hydrogen cyanide from cyanogenic glycosides. 

Fig. 2.13 Generalized reaction sequence from starting amino acid [65] to product cyanogenic glycoside [66]...

L. corniculatus in southern England, and demonstrated that presence of cyanogenic glycosides is dominant over their absence. Further work on inheritance of cyano-genesis in this species was complicated by the fact that this clover is a tetraploid. Work with other species led to more definitive results, however. 

Fig. 2.14 Generalized pattern of distribution of cyanogenic glycosides in Europe...

A few paragraphs above, we saw the part played by Lotus corniculatus in the cyanogenic glycoside story. We now turn onr attention to another aspect of this species that has attracted a considerable amonnt of attention and has, coincidentally. 

The authors suggest that altitudinal variation in phytochemical constituents remains unknown. That this is factually incorrect is revealed by the well-known work on the effect of elevation on cyanogenic glycosides, as shown in the case of the clovers above, as well as in the case of alkaloid variation in Berberis just described. 

Fig. 6.2 Compounds 519-524, cyanogenic glycosides from Passiflora species...

Atwood, S. S. and Sullivan, J. T. 1943. Inheritance of a cyanogenic glycoside and its hydrolyzing enzyme in Trifolium repens. J. Heredity 34 311-320. 

Jones, D. A. 1972. Cyanogenic glycosides and their function. Pages 103-124 in J. B. Harbome (ed.). Phytochemical Ecology, Academic Press, New York. 

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). 

Most cyanogenic glycosides are biogenetically derived from the amino acids phenylalanine, tyrosine, valine, isoleucine, or leucine but the non-protein amino acid cyclopentenylglycine and probably, nicotinic acid also serve as precursors (Figure 5.1) [9]. 

Figure 5.1 Cyanogenic glycosides derived from amino acids (and nicotinic acid)...

Siegler, D.S. and Brinker, A.M. (1993) Characterisation of cyanogenic glycoside, cyanolipids, nitroglycosides, organic nitro compounds and nitrile glycosides from plants, in Methods of Plant Biochemistry, Alkaloids and Sulfur Compounds (eds P.M. Dey and J.B. Harbome) Academic Press, pp. 51—93. 

Lechtenberg, M. and Nahrstedt, A. (1999) Cyanogenic glycosides, in Naturally Occurring Glycosides (ed. R. Ikan) John Wiley Sons, Ltd, Chichester, UK, pp. 147-191. 

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