Allicin is an
organosulfur compound
Organosulfur chemistry is the study of the properties and synthesis of organosulfur compounds, which are organic compounds that contain sulfur. They are often associated with foul odors, but many of the sweetest compounds known are organosulfur der ...
obtained from
garlic
Garlic (''Allium sativum'') is a species of bulbous flowering plants in the genus '' Allium''. Its close relatives include the onion, shallot, leek, chives, Welsh onion, and Chinese onion. Garlic is native to central and south Asia, str ...
and
leeks
A leek is a vegetable, a cultivar of '' Allium ampeloprasum'', the broadleaf wild leek ( syn. ''Allium porrum''). The edible part of the plant is a bundle of leaf sheaths that is sometimes erroneously called a "stem" or "stalk".
The genus '' ...
.
When fresh garlic is chopped or crushed, the enzyme
alliinase
In enzymology, an alliin lyase () is an enzyme that catalyzes the chemical reaction
:an ''S''-alkyl-L-cysteine ''S''-oxide \rightleftharpoons an alkyl sulfenate + 2-aminoacrylate
Hence, this enzyme has one substrate, ''S''-alkyl-L-cysteine ...
converts
alliin
Alliin is a sulfoxide that is a natural constituent of fresh garlic. It is a derivative of the amino acid cysteine. When fresh garlic is chopped or crushed, the enzyme alliinase converts alliin into allicin, which is responsible for the aroma o ...
into allicin, which is responsible for the aroma of fresh garlic. Allicin is unstable and quickly changes into a series of other sulfur-containing compounds such as
diallyl disulfide
Diallyl disulfide (DADS or 4,5-dithia-1,7-octadiene) is an organosulfur compound derived from garlic and a few other plants in the genus ''Allium''. Along with diallyl trisulfide and diallyl tetrasulfide, it is one of the principal components of ...
.
Allicin is an
antifeedant
Antifeedants are organic compounds produced by plants to repel herbivores through distaste or toxicity. These chemical compounds are typically classified as secondary metabolites in that they are not essential for the metabolism of the plant, but ...
, i.e. the defense mechanism against attacks by pests on the garlic plant.
Allicin is an oily, slightly yellow liquid that gives garlic its distinctive odor. It is a
thioester
In organic chemistry, thioesters are organosulfur compounds with the molecular structure . They are analogous to carboxylate esters () with the sulfur in the thioester replacing oxygen in the carboxylate ester, as implied by the thio- prefix ...
of
sulfenic acid
In chemistry, a sulfenic acid is an organosulfur compound and oxoacid with the general formula . It is the first member of the family of organosulfur oxoacids, which also include sulfinic acids () and sulfonic acids (), respectively. The base mem ...
. It is also known as allyl thiosulfinate.
Its biological activity can be attributed to both its antioxidant activity and its reaction with thiol-containing proteins.
Structure and occurrence
Allicin features the
thiosulfinate
In organosulfur chemistry, thiosulfinate is a functional group consisting of the linkage (R refers to organic substituents). Thiolsulfinates are also named as alkanethiosulfinic (or arenethiosulfinic) acid esters.
They are the first of the seri ...
functional group, R-S-(O)-S-R. The compound is not present in garlic unless tissue damage occurs,
and is formed by the action of the enzyme
alliinase
In enzymology, an alliin lyase () is an enzyme that catalyzes the chemical reaction
:an ''S''-alkyl-L-cysteine ''S''-oxide \rightleftharpoons an alkyl sulfenate + 2-aminoacrylate
Hence, this enzyme has one substrate, ''S''-alkyl-L-cysteine ...
on
alliin
Alliin is a sulfoxide that is a natural constituent of fresh garlic. It is a derivative of the amino acid cysteine. When fresh garlic is chopped or crushed, the enzyme alliinase converts alliin into allicin, which is responsible for the aroma o ...
.
Allicin is
chiral
Chirality () is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek language, Greek (''kheir''), "hand", a familiar chiral object.
An object or a system is ''chiral'' if it is dist ...
but occurs naturally only as a
racemate
In chemistry, a racemic mixture or racemate () is a mixture that has equal amounts (50:50) of left- and right-handed enantiomers of a chiral molecule or salt. Racemic mixtures are rare in nature, but many compounds are produced industrially as r ...
.
The
racemic
In chemistry, a racemic mixture or racemate () is a mixture that has equal amounts (50:50) of left- and right-handed enantiomers of a chiral molecule or salt. Racemic mixtures are rare in nature, but many compounds are produced industrially as r ...
form can also be generated by oxidation of
diallyl disulfide
Diallyl disulfide (DADS or 4,5-dithia-1,7-octadiene) is an organosulfur compound derived from garlic and a few other plants in the genus ''Allium''. Along with diallyl trisulfide and diallyl tetrasulfide, it is one of the principal components of ...
:
:(SCH
2CH=CH
2)
2 + 2 RCO
3H + H
2O → 2 CH
2=CHCH
2SOH + 2 RCO
2H
:2 CH
2=CHCH
2SOH → CH
2=CHCH
2S(O)SCH
2CH=CH
2 + H
2O
Alliinase is irreversibly deactivated below pH 3; as such, allicin is generally not produced in the body from the consumption of fresh or powdered garlic. Furthermore, allicin can be unstable, breaking down within 16 hours at 23 °C.
Biosynthesis
The biosynthesis of allicin commences with the conversion of cysteine into
''S''-allyl-L-cysteine. Oxidation of this thioether gives the sulfoxide (
alliin
Alliin is a sulfoxide that is a natural constituent of fresh garlic. It is a derivative of the amino acid cysteine. When fresh garlic is chopped or crushed, the enzyme alliinase converts alliin into allicin, which is responsible for the aroma o ...
). The enzyme
alliinase
In enzymology, an alliin lyase () is an enzyme that catalyzes the chemical reaction
:an ''S''-alkyl-L-cysteine ''S''-oxide \rightleftharpoons an alkyl sulfenate + 2-aminoacrylate
Hence, this enzyme has one substrate, ''S''-alkyl-L-cysteine ...
, which contains
pyridoxal phosphate
Pyridoxal phosphate (PLP, pyridoxal 5'-phosphate, P5P), the active form of vitamin B6, is a coenzyme in a variety of enzymatic reactions. The International Union of Biochemistry and Molecular Biology has catalogued more than 140 PLP-dependen ...
(PLP), cleaves alliin, generating allylsulfenic acid (CH
2=CHCH
2SOH), pyruvate, and ammonium ions.
At room temperature, two molecules of allylsulfenic acid condense to form allicin.
[
]
Research
Allicin has been studied for its potential to treat various kinds of multiple drug resistance
Multiple drug resistance (MDR), multidrug resistance or multiresistance is antimicrobial resistance shown by a species of microorganism to at least one antimicrobial drug in three or more antimicrobial categories. Antimicrobial categories are ...
bacterial infections, as well as viral and fungal infections in vitro
''In vitro'' (meaning ''in glass'', or ''in the glass'') Research, studies are performed with Cell (biology), cells or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in ...
, but as of 2016, the safety and efficacy of allicin to treat infections in people was unclear.
A Cochrane review found there to be insufficient clinical evidence regarding the effects of allicin in preventing or treating common cold
The common cold, or the cold, is a virus, viral infectious disease of the upper respiratory tract that primarily affects the Respiratory epithelium, respiratory mucosa of the human nose, nose, throat, Paranasal sinuses, sinuses, and larynx. ...
.
History
It was first isolated and studied in the laboratory by Chester J. Cavallito and John Hays Bailey in 1944.[
Allicin was discovered as part of efforts to create ]thiamine
Thiamine, also known as thiamin and vitamin B1, is a vitamin – an Nutrient#Micronutrients, essential micronutrient for humans and animals. It is found in food and commercially synthesized to be a dietary supplement or medication. Phosp ...
derivatives in the 1940s, mainly in Japan. Allicin became a model for medicinal chemistry
Medicinal or pharmaceutical chemistry is a scientific discipline at the intersection of chemistry and pharmacy involved with drug design, designing and developing pharmaceutical medication, drugs. Medicinal chemistry involves the identification, ...
efforts to create other thiamine disulfides. The results included sulbutiamine
Sulbutiamine sold under the brand names Arcalion, Enerion, and Sulbuxin is a synthetic derivative of thiamine (vitamin B1). In France, it is used to treat symptoms of weakness or fatigue. In Uruguay, it is prescribed when there is thiamine defic ...
, fursultiamine
Fursultiamine (INN; chemical name thiamine tetrahydrofurfuryl disulfide or TTFD; brand names Adventan, Alinamin-F, Benlipoid, Bevitol Lipophil, Judolor, Lipothiamine) is a medication and vitamin used to treat thiamine deficiency. Chemically, it ...
(thiamine tetrahydrofurfuryl disulfide) and benfothiamine. These compounds are hydrophobic, easily pass from the intestines to the bloodstream, and are reduced to thiamine by cysteine or glutathione
Glutathione (GSH, ) is an organic compound with the chemical formula . It is an antioxidant in plants, animals, fungi, and some bacteria and archaea. Glutathione is capable of preventing damage to important cellular components caused by sources ...
.
See also
* Allyl isothiocyanate
Allyl isothiocyanate (AITC) is a naturally occurring unsaturated isothiocyanate. The colorless oil is responsible for the pungent taste of cruciferous vegetables such as mustard, radish, horseradish, and wasabi. This pungency and the lachrymato ...
, the active piquant chemical in mustard
Mustard may refer to:
Food and plants
* Mustard (condiment), a paste or sauce made from mustard seeds used as a condiment
* Mustard plant, one of several plants, having seeds that are used for the condiment
** Mustard seed, small, round seeds of ...
, radish
The radish (''Raphanus sativus'') is a flowering plant in the mustard family, Brassicaceae. Its large taproot is commonly used as a root vegetable, although the entire plant is edible and its leaves are sometimes used as a leaf vegetable. Origina ...
es, 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 ...
and wasabi
Wasabi (Japanese language, Japanese: , , or , ) or Japanese horseradish (''Eutrema japonicum'' syn. ''Wasabia japonica'') is a plant of the family Brassicaceae, which also includes horseradish and Mustard plant, mustard in other genus, genera. ...
* ''syn''-Propanethial-''S''-oxide, the lachrymatory chemical found in onion
An onion (''Allium cepa'' , from Latin ), also known as the bulb onion or common onion, is a vegetable that is the most widely cultivated species of the genus '' Allium''. The shallot is a botanical variety of the onion which was classifie ...
s
* List of phytochemicals in food
The following is a list of phytochemicals present in foods.
Terpenoids (isoprenoids)
Carotenoids ( tetraterpenoids)
''Carotenes''
orange pigments
* α-Carotene – to vitamin A: carrots, pumpkins, maize, tangerine, orange
* β-Carote ...
References
{{Authority control
Thiosulfinates
Anti-inflammatory agents
Antibiotics
Dietary antioxidants
Pungent flavors
Allium
Garlic
Antifungals
Allyl compounds
Transient receptor potential channel modulators