Sinigrin or allyl glucosinolate is a

glucosinolate Glucosinolates are natural components of many pungent plants such as mustard, cabbage, and horseradish. The pungency of those plants is due to mustard oils produced from glucosinolates when the plant material is chewed, cut, or otherwise damaged. ...

that belongs to the family of

glucoside A glucoside is a glycoside that is chemically derived from glucose. Glucosides are common in plants, but rare in animals. Glucose is produced when a glucoside is hydrolysed by purely chemical means, or decomposed by fermentation or enzymes. Th ...

s found in some plants of the family

Brassicaceae Brassicaceae () or (the older but equally valid) Cruciferae () is a medium-sized and economically important Family (biology), family of flowering plants commonly known as the mustards, the crucifers, or the cabbage family. Most are herbaceous pla ...

such as Brussels sprouts,

broccoli Broccoli (''Brassica oleracea'' var. ''italica'') is an edible green plant in the Brassicaceae, cabbage family (family Brassicaceae, genus ''Brassica'') whose large Pseudanthium, flowering head, plant stem, stalk and small associated leafy gre ...

, and the seeds of black mustard (''

Brassica nigra ''Rhamphospermum nigrum'' (syns. ''Brassica nigra'' and ''Sinapis nigra''), black mustard, is an annual plant native to cooler regions of North Africa, temperate regions of Europe, and parts of Asia. It is cultivated for its dark-brown-to-black se ...

''). Whenever sinigrin-containing plant tissue is crushed or otherwise damaged, the

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

myrosinase degrades sinigrin to a mustard oil ( allyl isothiocyanate), which is responsible for the

pungent Pungency ( ) is the taste of food commonly referred to as spiciness, hotness or heat, found in foods such as chili peppers. Highly pungent tastes may be experienced as unpleasant. The term piquancy ( ) is sometimes applied to foods with a lower ...

taste of mustard and

horseradish Horseradish (''Armoracia rusticana'', syn. ''Cochlearia armoracia'') is a perennial plant of the family Brassicaceae (which also includes Mustard plant, mustard, wasabi, broccoli, cabbage, and radish). It is a root vegetable, cultivated and us ...

. Seeds of white mustard, ''Sinapis alba'', give a less pungent mustard because this species contains a different glucosinolate, sinalbin.

Occurrence

The compound was first reported in 1839, after its isolation from black mustard ''

'', also known as ''Sinapis nigra'', after which it was named. Sinigrin is now known to occur widely in other brassica families including

and

Capparaceae The Capparaceae (or Capparidaceae), commonly known as the caper family, are a family of plants in the order Brassicales. As currently circumscribed, the family contains 15 genera and about 430 species. The largest genera are ''Capparis'' (about 1 ...

Structure

The chemical structure of sinigrin had been established by 1930. This showed that it is a glucose derivative with β-D-glucopyranose configuration. It was unclear whether the C=N bond was in the Z (or ''syn'') form, with sulfur and oxygen substituents on the same side of the double bond, or the alternative E form in which they are on opposite sides. The matter was settled by

X-ray crystallography X-ray crystallography is the experimental science of determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to Diffraction, diffract in specific directions. By measuring th ...

of its potassium salt in 1963. It is now known that all natural

glucosinolates Glucosinolates are natural components of many pungent plants such as mustard, cabbage, and horseradish. The pungency of those plants is due to mustard oils produced from glucosinolates when the plant material is chewed, cut, or otherwise dama ...

are of Z form.

Synthesis

Biosynthesis

Sinigrin is biosynthesised from the amino acid

methionine Methionine (symbol Met or M) () is an essential amino acid in humans. As the precursor of other non-essential amino acids such as cysteine and taurine, versatile compounds such as SAM-e, and the important antioxidant glutathione, methionine play ...

in a multi-step pathway.

Laboratory synthesis

The first laboratory syntheses of sinigrin was published in 1965. Later work provided a more efficient route.

Function

The natural role of glucosinolates are as plant defense compounds. The enzyme myrosinase removes the glucose group in sinigrin to give an intermediate which spontaneously rearranges to allyl isothiocyanate, the compound responsible for the pungent taste of

Dijon mustard Dijon mustard () is a traditional mustard of France. It is named after the city of Dijon in Burgundy, which was the center of mustard making in the late Middle Ages and was granted exclusive rights in France in the 17th century. First used in ...

. This is a reactive material which is toxic to many insect predators and its production is triggered when the plant is damaged. This effect has been called the mustard oil bomb. Singrin is also known to be allelopathic. At concentrations typically found in foods, the glucosinolates are not toxic to humans and can be useful flavor components. Sinigrin is unusual among the glucosinolates because it is also known to be the natural precursor for other volatile compounds including epithionitrile, allyl cyanide and allyl thiocyanate.

References

{{Glycosides Pungent flavors Glucosinolates Allyl compounds Potassium compounds Sulfate esters