Linamarin - a cyanogenic glucoside – University of Copenhagen

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NaToxAq > Toxin of the week > Linamarin

22 May 2017

Linamarin - a cyanogenic glucoside

Natural toxin

Cyanogenic glucosides are common in crop and non-crop plants. On hydrolysis toxic hydrogencyanide is produced; both intact cyanogenic glucosides and hydrogencyanide may leach through soils

Linamarin. Click image for 3D structure

The natural toxin Linamarin (CAS 554-35-8) is present in for instance flax (Linum usitatissimum), cassava (Manihot esculenta), lima beans (Phaseolus lunatus) and white clover (Trifolium repens).  Linmarin belongs to the family of cyanogenic glucosides which are present in more than 2500 plant species.

Cyanogenic glucosides functions as deterrents or toxins towards feeding insects; some insects even have developed mechanisms by which they can sesquester or degrade ingested cyanogenic glucosides. When cyanogenic glucosides are hydrolysed, usually in presence of glucosidase (linamarase) and lyase enzymes, toxic hydrogen cyanide (HCN) is released. White clover contains up to 1 gram of cyanide per kg DM, while bitter varieties of cassava can have much higher contents. Fatal doses of HCN for vertebrates can be as low as 1 mg HCN per kg.  Crops containing cyanogenic glucosides need to properly processes (leached, cooked, fermented etc) before use as food. 

Linamarin is a highly polar glucosidic compound (log Kow -1.8) and thus it hardly sorbs to soils and it is readily leached. Linamarin is most stable in cold environments that are slightly acidic, which have low microbial activity (half lives of hundreds of hours). Fast hydrolysis and formation of HCN is seen in top soils; the released cyanide forsorbs to soil minerals or is degraded. The extent of leaching of linamarin as well as HCN in the field has never been investigated.

SMILES: CC(C)(C#N)O[C@H]1[C@@H]([C@H]([C@@H]([C@H](O1)CO)O)O)O

References:

  • Bjarnholt, N.B.; Lægdsmand, M.; Hansen, H.C.B.;.Møller, B.L. (2008) Leaching of cyanogenic glucosides and cyanide from white clover green manure. Chemosphere 72, 897 - 904.
  • Vetter, J. (2000) Plant cyanogenic glucosides. Toxicon 38, 11 – 36
  • Zagrobelny, M.; Bak, S.; Rasmussen, A.V.; Jørgensen, B.; Naumann, C.M.; Møller, B.L. (2004) Cyanogenic glucosides and plant-insect interactions. Phytochem. 65, 293 – 306
  • Johansen, H.; Rasmussen, L.H.; Olsen, C.E.; Hansen, H.C.B. (2007) Hydrolysis, sorption and degradation of the cyanogenic glycoside – dhurrin – in soil. Chemosphere 67, 259 - 266.