Allicin

Allicin
Preferred IUPAC name 2-Propene-1-sulfinothioic acid S-2-propenyl ester
Systematic name 3-[(Prop-2-ene-1-sulfinyl)sulfanyl]prop-1-ene
Identifiers
CAS number	539-86-6 Y
PubChem	65036
ChemSpider	58548 Y
UNII	3C39BY17Y6 Y
EC number	208-727-7
KEGG	C07600 Y
MeSH	Allicin
ChEBI	CHEBI:28411 Y
ChEMBL	CHEMBL359965 Y
IUPHAR ligand	2419
Beilstein Reference	1752823
Jmol-3D images	Image 1 Image 2
SMILES O=S(SC\C=C)C\C=C C=CCSS(=O)CC=C
InChI InChI=1S/C6H10OS2/c1-3-5-8-9(7)6-4-2/h3-4H,1-2,5-6H2 Y Key: JDLKFOPOAOFWQN-UHFFFAOYSA-N Y InChI=1/C6H10OS2/c1-3-5-8-9(7)6-4-2/h3-4H,1-2,5-6H2 Key: JDLKFOPOAOFWQN-UHFFFAOYAO
Properties
Molecular formula	C6H10OS2
Molar mass	162.27 g mol−1
Exact mass	162.017306322 g mol−1
Appearance	Colourless liquid
Density	1.112 g cm−3
Melting point	<25 °C
Boiling point	decomposes
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Allicin is an organosulfur compound obtained from garlic, a species in the family Alliaceae.^[1] It was first isolated and studied in the laboratory by Chester J. Cavallito and John Hays Bailey in 1944.^[2][3] This colorless liquid has a distinctively pungent smell. This compound exhibits antibacterial and anti-fungal properties.^[2] Allicin is garlic's defense mechanism against attacks by pests.^[4]

Structure and occurrence

Allicin features the thiosulfinate functional group, R-S(O)-S-R. The compound is not present in garlic unless tissue damage occurs,^[1] and is formed by the action of the enzyme alliinase on alliin.^[1] Allicin is chiral but occurs naturally only as a racemate.^[3] The racemic form can also be generated by oxidation of diallyl disulfide:^[5]

(SCH₂CH=CH₂)₂ + RCO₃H → CH₂=CHCH₂S(O)SCH₂CH=CH₂ + RCO₂H

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.^[6][7] Furthermore, allicin can be unstable, breaking down within 16 h at 23 °C.^[8]

Potential health benefits

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Several animal studies published between 1995 and 2005 indicate that allicin may: reduce atherosclerosis and fat deposition,^[9][10] normalize the lipoprotein balance, decrease blood pressure,^[11][12] have anti-thrombotic^[13] and anti-inflammatory activities, and function as an antioxidant to some extent.^[14][15][16] Other studies have shown a strong oxidative effect in the gut that can damage intestinal cells, although these results were in laboratory animals, not humans. Furthermore, many of these results were obtained by excessive amounts of allicin, which has been clearly shown to have some toxicity at high amounts, or by physically injecting the lumen itself with allicin, which may not be indicative of what would happen via oral ingestion of allicin or garlic supplements.^{[17] [18]} A randomized clinical trial funded by the National Institutes of Health (NIH) in the United States and published in the Archives of Internal Medicine in 2007 found that the consumption of garlic in any form did not reduce blood cholesterol levels in patients with moderately high baseline cholesterol levels.^[19] The fresh garlic used in this study contained substantial levels of allicin so this study casts doubt on the ability of allicin when taken orally to reduce blood cholesterol levels in human subjects.

In 2009, Vaidya, Ingold and Pratt clarified the mechanism of the antioxidant activity of garlic, such as trapping damaging free radicals. When allicin decomposes, it forms 2-propenesulfenic acid, and this compound is what binds to the free-radicals.^[20] The 2-propenesulfenic formed when garlic is cut or crushed has a lifetime of less than one second.^[21]

Antibacterial activity

Allicin has been found to have numerous antimicrobial properties, and has been studied in relation to both its effects and its biochemical interactions.^[22] One potential application is in the treatment of methicillin-resistant Staphylococcus aureus (MRSA), an increasingly prevalent concern in hospitals. A screening of allicin against 30 strains of MRSA found high level of antimicrobial activitity, including against strains that are resistant to other chemical agents.^[23] Of the strains tested, 88% had minimum inhibitory concentrations for allicin liquids of 16 mg/L, and all strains were inhibited at 32 mg/L. Furthermore, 88% of clinical isolates had minimum bactericidal concentrations of 128 mg/L, and all were killed at 256 mg/L. Of these strains, 82% showed intermediate or full resistance to mupirocin. This same study examined use of an aqueous cream of allicin, and found it somewhat less effective than allicin liquid. At 500 mg/L, however, the cream was still active against all the organisms tested—which compares well with the 20 g/L mupirocin currently used for topical application.^[23]

A water-based formulation of purified allicin was found to be more chemically stable than other preparations of garlic extracts.^[23] They proposed that the stability may be due to the hydrogen bonding of water to the reactive oxygen atom in allicin and also to the absence of other components in crushed garlic that destabilize the molecule.^[24] (Presumably, the dilution of these components in water helps to preserve the allicin molecule.)

See also

Wikimedia Commons has media related to: allicin

• Allyl isothiocyanate, the active piquant chemical in mustard, radishes, horseradish and wasabi
• Capsaicin, the active piquant chemical in chili peppers
• Piperine, the active piquant chemical in black pepper
• syn-Propanethial-S-oxide, the chemical found in onions
• List of phytochemicals in food

References

External links

• Johnston, Nicole (2002). "News in Brief: Garlic: A natural antibiotic". Mdd modern drug discovery 5 (4). http://pubs.acs.org/subscribe/journals/mdd/v05/i04/html/04news4.html. "Allicin, the major component of garlic, is one such agent, and it was recently shown to be potent against VRE and MRSA in two studies presented at the 41st Interscience Conference on Antimicrobial Agents and Chemotherapy in Chicago in December." 

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