ALLICIN SYNTHESIS

Allicin can be obtained from crushed garlic. When garlic cloves are mashed, the allinase enzyme and the substrate alliin previously stored in separate vesicles come in contact and allicin is formed acording to:


Allyl sulfenic condense to give allicin


Allicin can be synthesized in the laboratory by oxidation of diallyl disulfide with a peroxide as hydrogen peroxide , metachloro perbenzoic acid or magnesium monoperoxy phthalate. A detailed description of this last reaction is found at

"Allicin synthesis"

The chemical behavior of allicin is that of thiosulfinates, R-S--S(O)-R (1). Its physical properties, compared with other thiosulfinates, were first studied by Chester Cavallito and co-workers(2,3). In this section the most characteristics reactions are described. The reader may consult specific literature cited below
- Alkaline hydrolysis
In alkaline medium, allicin hydrolyzes to yield a disulfide and a sulfinate ion (2,4)
*

Reaction with thiols

This reaction is specially interesting in the case of cysteine, and has analytical applications (5). Enzymes containing SH active groups (e.g. papain) can be inactivated by allicin.

Allicin is an oily liquid, water soluble at 2.5% (3) with a characteristic odor (not as pungent as diallyl disulfide). At room temperature it decomposes almost totally in a 48h period (it can be stored for months at -70
oC or below). The reactions involved in the process have been thoroughly studied by E. Block. At the first stage the allicin breaks the SS bond to yield two compounds:

Thioacrolein can condense in a Diels-Alder reaction


Allicin itself can condense at room temperature to form two compounds named E and Z "ajoenes" (from Spanish word "ajo" from the Latin"allium" =garlic). A complex mechanism has been proposed for these reactions (6)

E-ajoene

Z-ajoene


The formation of these products and their relative proportion depends on the nature of the solvent. Thus when crushed garlic is stored in water the ajoenes and disulfides form to a lesser extent than in ethanol or oil (7) so that water is the solvent generally used for long term storage of allicin (at low temperature). An example of the variety and complexity of the allicin chemistry in non aqueous solvents is a new product found in oil-macerated garlic: Z- 4, 5, 9-trithiadeca- 1-6-diene - 9-oxide or Z-10 devinyl ajoene (8). This compound shows a broad antimicrobial activity comparable to Z -ajoene


Z10 DA
References

1.Sir Derek Barton& David Ollis chairmenComprehensive Organic Chemistry . Selenium and Sulfur Compounds;Pergamon Press. VOL 3, p 294

2.Cavallito, C.J. and Bailey, J.H. Allicin, the antibacterial principe of Allium sativum. I. Isolation, physical properties and antibacterial action. J. Am. Chem. Soc 65, 1950-1951,(1944)

3.Small, L.V., Bayley, J.H., and Cavallito,C. Alkyl thiosulfinates J. Am. Chem. Soc,69,1710-1713,(1947)

4.Kice,J.L., Rogers,T.E. Mechanism of the Alkaline Hydrolysis of Aryl Thiosulfinates and Thiosulfonates J. Am. Chem. Soc 96,8009-8079, (1974)

5.Han, J.,Lawson, L.,Han, G. A Spectrophotometric Method for Quantitative Determination of Allicin and Total Garlic Thiosulfinates. Anal. Biochem. 225 157-160,(1995)

6.Block, E., Ahmad, S., Jain, M., Crecely, R., Apitz-Castro, R., Cruz, M. (E,Z)-ajoene: A potent antithrombotic agent from garlic. J. Am. Chem. Soc. 106, 8295-8296,(1984)

7. Iberl,B., Winkler,G, Knobloch,K. Products of Allicin Transformation: Ajoenes and Dithiins, Characterization and theeir Determination by HPLC. Planta Medica , 56, 202- 211, (1990)

8. Yoshida, H.,Iwata,N.,Katzusaki,H.,Naganawa,R.,Ishikawa,K.,Fukuda,H., Fujino,T. Suzuki,A. Antimicrobial Activity of a Compound Isolated from an Oil- Macerated Garlic Extract. Biosci. Biotechnol. Biochem, 62 , 1014-1017 (1998)

1 1 * In his original work Chester Cavallito referred to sulfur dioxide as the final product of alkaline hydrolysis. I have made the reaction in my lab, and I have analized the product by voltammetry. The product had the same halfwave potential than a standard sulfite voltammetric assay
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