Allicin

Not to be confused with Allysine or halicin.

Allicin is an organosulfur compound obtained from garlic.^[1] When fresh garlic is chopped or crushed, the enzyme alliinase converts alliin into allicin, which is responsible for the aroma of fresh garlic.^[2] Allicin is unstable and quickly changes into a series of other sulfur-containing compounds such as diallyl disulfide.^[3] Allicin is an antifeedant, i.e. the defense mechanism against attacks by pests on the garlic plant.^[4]

Allicin

Names
Preferred IUPAC name S-(Prop-2-en-1-yl) prop-2-ene-1-sulfinothioate
Other names 2-Propene-1-sulfinothioic acid S-2-propenyl ester 3-[(Prop-2-ene-1-sulfinyl)sulfanyl]prop-1-ene S-Allyl prop-2-ene-1-sulfinothioate
Identifiers
CAS Number	539-86-6 Y
3D model (JSmol)	Interactive image Interactive image
Beilstein Reference	1752823
ChEBI	CHEBI:28411 Y
ChEMBL	ChEMBL359965 Y
ChemSpider	58548 Y
ECHA InfoCard	100.007.935
EC Number	208-727-7
IUPHAR/BPS	2419
KEGG	C07600 Y
MeSH	Allicin
PubChem CID	65036
UNII	3C39BY17Y6 Y
CompTox Dashboard (EPA)	DTXSID6043707
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
SMILES O=S(SC\C=C)C\C=C C=CCSS(=O)CC=C
Properties
Chemical formula	C6H10OS2
Molar mass	162.26 g·mol−1
Appearance	Colourless liquid
Density	1.112 g cm−3
Melting point	< 25 °C (77 °F; 298 K)
Boiling point	decomposes
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Allicin is an oily, slightly yellow liquid that gives garlic its distinctive odor. It is a thioester of sulfenic acid. It is also known as allyl thiosulfinate.^[5] Its biological activity can be attributed to both its antioxidant activity and its reaction with thiol-containing proteins.^[6]

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.^[7] The racemic form can also be generated by oxidation of diallyl disulfide:^[8][9]

(SCH₂CH=CH₂)₂ + 2 RCO₃H + H₂O → 2 CH₂=CHCH₂SOH + 2 RCO₂H

2 CH₂=CHCH₂SOH → CH₂=CHCH₂S(O)SCH₂CH=CH₂ + H₂O

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.^[10][11] Furthermore, allicin can be unstable, breaking down within 16 hours at 23 °C.^[12]

Biosynthesis

The biosynthesis of allicin commences with the conversion of cysteine into S-allyl-L-cysteine. Oxidation of this thioether gives the sulfoxide (alliin). The enzyme alliinase, which contains pyridoxal phosphate (PLP), cleaves alliin, generating allylsulfenic acid (CH₂=CHCH₂SOH), pyruvate, and ammonium ions.^[6] At room temperature, two molecules of allylsulfenic acid condense to form allicin.^[5][9]

Research

Allicin has been studied for its potential to treat various kinds of multiple drug resistance bacterial infections, as well as viral and fungal infections in vitro, but as of 2016, the safety and efficacy of allicin to treat infections in people was unclear.^[13]

In a small clinical trial, a daily high dose of extracted allicin (20 times the amount in a garlic clove) showed effectiveness to prevent the common cold.^[14] A Cochrane review found this to be insufficient to draw conclusions.^[15]

A study from 2021 has shown "a combination of the short half-life, high reactivity and non-specificity to particular proteins are reasons most bacteria cannot deal with allicin’s mode of action and develop effective defence mechanism" and argue "that could be the key to sustainable drug design addressing serious problems with escalating emergence of multidrug-resistant bacterial strains".^[16]

History

It was first isolated and studied in the laboratory by Chester J. Cavallito and John Hays Bailey in 1944.^[17][7] Allicin was discovered as part of efforts to create thiamine derivatives in the 1940s, mainly in Japan. Allicin became a model for medicinal chemistry efforts to create other thiamine disulfides. The results included sulbutiamine, fursultiamine (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.^[18]: 302

See also

• Allyl isothiocyanate, the active piquant chemical in mustard, radishes, horseradish and wasabi
• syn-Propanethial-S-oxide, the lachrymatory chemical found in onions
• List of phytochemicals in food

References

1. Block E (March 1985). "The Chemistry of Garlic and Onions". Scientific American. 252 (3): 114–9. Bibcode:1985SciAm.252c.114B. doi:10.1038/scientificamerican0385-114. PMID 3975593.
2. Kourounakis PN, Rekka EA (November 1991). "Effect on active oxygen species of alliin and Allium sativum (garlic) powder". Research Communications in Chemical Pathology and Pharmacology. 74 (2): 249–52. PMID 1667340.
3. Ilic D, Nikolic V, Nikolic L, Stankovic M, Stanojevic L, Cakic M (2011). "Allicin and related compounds: Biosynthesis, synthesis and pharmacological activity" (PDF). Facta Universitatis. 9 (1): 9–20. doi:10.2298/FUPCT1101009I.
4. Borlinghaus J, Albrecht F, Gruhlke MC, Nwachukwu ID, Slusarenko AJ (August 2014). "Allicin: chemistry and biological properties". Molecules. 19 (8): 12591–618. doi:10.3390/molecules190812591. PMC 6271412. PMID 25153873.
5. Nikolic V, Stankovic M, Nikolic L, Cvetkovic D (January 2004). "Mechanism and kinetics of synthesis of allicin". Die Pharmazie. 59 (1): 10–4. PMID 14964414.
6. Rabinkov A, Miron T, Konstantinovski L, Wilchek M, Mirelman D, Weiner L (February 1998). "The mode of action of allicin: trapping of radicals and interaction with thiol containing proteins". Biochimica et Biophysica Acta (BBA) - General Subjects. 1379 (2): 233–44. doi:10.1016/s0304-4165(97)00104-9. PMID 9528659.
7. Block E (2010). Garlic and Other Alliums: The Lore and the Science. Cambridge: Royal Society of Chemistry. ISBN 978-0854041909.
8. Cremlyn RJ (1996). An introduction to organosulfur chemistry. Wiley. ISBN 0-471-95512-4.
9. Borlinghaus J, Albrecht F, Gruhlke MC, Nwachukwu ID, Slusarenko AJ (August 2014). "Allicin: chemistry and biological properties". Molecules. 19 (8): 12591–618. doi:10.3390/molecules190812591. PMC 6271412. PMID 25153873.
10. Brodnitz MH, Pascale JV, Derslice LV (1971). "Flavor components of garlic extract". Journal of Agricultural and Food Chemistry. 19 (2): 273–5. doi:10.1021/jf60174a007.
11. Yu TH, Wu CM (1989). "Stability of Allicin in Garlic Juice". Journal of Food Science. 54 (4): 977. doi:10.1111/j.1365-2621.1989.tb07926.x.
12. Hahn G (1996). Koch HP, Lawson LD (eds.). Garlic: the science and therapeutic application of Allium sativum L and related species (2nd ed.). Baltimore: Williams and Wilkins. pp. 1–24. ISBN 978-0-683-18147-0.
13. Marchese A, Barbieri R, Sanches-Silva A, Daglia M, Nabavi SF, Jafari NJ, Izadi M, Ajami M, Nabavi SM (2016). "Antifungal and antibacterial activities of allicin: A review". Trends in Food Science and Technology. 52: 49–56. doi:10.1016/j.tifs.2016.03.010.
14. Nahas R, Balla A (January 2011). "Complementary and alternative medicine for prevention and treatment of the common cold". Canadian Family Physician. 57 (1): 31–6. PMC 3024156. PMID 21322286.
15. Lissiman E, Bhasale AL, Cohen M (November 2014). "Garlic for the common cold". The Cochrane Database of Systematic Reviews. 2020 (11): CD006206. doi:10.1002/14651858.CD006206.pub4. PMC 6465033. PMID 25386977.
16. Janská P, Knejzlík Z, Perumal AS, Jurok R, Tokárová V, Nicolau DV, et al. (2021-03-19). "Effect of physicochemical parameters on the stability and activity of garlic alliinase and its use for in-situ allicin synthesis". PLOS ONE. 16 (3): e0248878. Bibcode:2021PLoSO..1648878J. doi:10.1371/journal.pone.0248878. PMC 7978267. PMID 33740023.
17. Cavallito CJ, Bailey JH (1944). "Allicin, the Antibacterial Principle of Allium sativum. I. Isolation, Physical Properties and Antibacterial Action". Journal of the American Chemical Society. 66 (11): 1950. doi:10.1021/ja01239a048.
18. Bettendorff L (2014). "Chapter 7 - Thiamine". In Zempleni J, Suttie JW, Gregory JF, Stover PJ (eds.). Handbook of vitamins (Fifth ed.). Hoboken: CRC Press. pp. 267–324. ISBN 978-1-4665-1557-4.