Allicin

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] When fresh garlic is chopped or crushed, the enzyme alliinase converts alliin into allicin, which is responsible for the aroma of fresh garlic.[4] The allicin generated is unstable and quickly changes into a series of other sulfur-containing compounds such as diallyl disulfide.[5] Allicin is part of a defense mechanism against attacks by pests on the garlic plant.[6]

Not to be confused with halicin.
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
3D model (JSmol)
1752823
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.007.935
EC Number
  • 208-727-7
KEGG
MeSH Allicin
UNII
Properties
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 unique odor. It is a thioester of sulfenic acid and is also known as allyl thiosulfinate.[7] Its biological activity can be attributed to both its antioxidant activity and its reaction with thiol-containing proteins.[8] Produced in garlic cells, allicin is released upon disruption, producing a potent characteristic scent when garlic is cut or cooked.[5][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.[3] The racemic form can also be generated by oxidation of diallyl disulfide:[9][10]

(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.[11][12] Furthermore, allicin can be unstable, breaking down within 16 hours at 23 °C.[13]

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.[8] At room temperature, two molecules of allylsulfenic acid condense to form allicin.[7][10]

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.[14]

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.[15] A Cochrane review found this to be insufficient to draw conclusions.[16]

History

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.[17]:302

See also

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. 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.
  3. Block E (2010). Garlic and Other Alliums: The Lore and the Science. Cambridge: Royal Society of Chemistry.
  4. 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.
  5. 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.
  6. 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.
  7. 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.
  8. 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.
  9. Cremlyn RJ (1996). An introduction to organosulfur chemistry. Wiley. ISBN 0-471-95512-4.
  10. Borlinghaus, Jan; Albrecht, Frank; Gruhlke, Martin; Nwachukwu, Ifeanyi; Slusarenko, Alan (2014). "Allicin: Chemistry and Biological Properties". Molecules. 19 (8): 12591–12618. doi:10.3390/molecules190812591. PMC 6271412. PMID 25153873.
  11. 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.
  12. Yu T, Wu C (1989). "Stability of Allicin in Garlic Juice". Journal of Food Science. 54 (4): 977. doi:10.1111/j.1365-2621.1989.tb07926.x.
  13. 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.
  14. 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.
  15. 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.
  16. Lissiman E, Bhasale AL, Cohen M (November 2014). "Garlic for the common cold". The Cochrane Database of Systematic Reviews (11): CD006206. doi:10.1002/14651858.CD006206.pub4. PMC 6465033. PMID 25386977.
  17. 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.
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