Allicin formation

Scheme 10 The formation of allicin from alliin by alliinase action...

Ajoene (Spanish, ajo, garlic), 4,5,9-trithiadodeca-l,6,ll-triene-9-oxide 35 (Scheme 12), an antithrombotic compound with other well-defined physiological properties, is formed from allicin.84 Like allicin, ajoene is a sulfoxide but has two further sulfur atoms in a disulfide linkage. E and Z isomeric forms are possible involving the C=C bond at positions 6 and 7. Ajoene is somewhat more stable than allicin. The formation of ajoene probably involves condensation of 2 molecules of allicin forming a sulfonium salt 33, with elimination of propenesulfenic acid. Elimination of a second molecule of propenesulfenic acid... 

Abramovitz, D., Gavri, S., Harats, D., Levkovitz, H., Mirelman, D., Miron, T., Eilat-Adar, S., Rabinkov, A., Wilchek, M., Eldar, M., and Vered, Z. 1999. Allicin-induced decrease in formation of fatty streaks (atherosclerosis) in mice fed a cholesterol-rich diet. Coron. Artery Dis. 10, 515-519. 

Members of the allium family (onions, garlic, and leeks) contain cysteine sulfoxide derivatives (allyl sulfur compounds), such as allicin and alliin (see Figure 14.9). When the plant cells are damaged, the enzyme alliinase is released from vacuoles and catalyzes the formation of thiosulfinates and thiols, including the lachrymator thiopropanal S-oxide. Their function in the plant is presumably to provide protection against attack by pests. 

Scheme (2). Formation of allicin from the action of allinase on alliin. (modified from Block et.al. 1984 [13]).

Boiling of whole cloves inactivates the enzyme allinase and only 0.5-1% of alliin is converted to allicin which is rapidly converted to diallyl trisulfide. Also 12% of the y-glutamylcysteines are hydrolyzed to S-allyl cysteine (SAC) and S-l-propenyl cysteine. A similar loss of alliin is found [37]. Boiling of crushed or tiny chopped garlic enables tiie formation of allicin... 

Alliin-inosine 5 -monophosphate thermal interactions, 188-197 Allium chemistry allicin decomposition, 67-68 previous studies, 64-66 natural flavor identification, 63-64 product formation from chopped garlic, 65... 

Galano A, Francisco-Marquez M (2009) Peroxyl radical scavenging activity of garlic 2-propenesulfenic acid vs allicin. J Phys Chem B 113 16077-16081 Galano A, Francisco-Marquez M (2009) Reactions of OOH radical with P-carotene, lycopene, and torulene hydrogen atom transfer and adduct formation mechanisms. J Phys ChemB 113 11338-11345... 

A number of enzymes have been reported which decompose thiamine without separating the two ring moieties. Thus garlic and certain other plants possess an enz nne which catalyzes formation of a disulfide from thiamine and allicin [Eq. (8)]. Presumably thiamine reacts in the thiol form (Se, S7). 

One study found that thiosulfinates (e.g., allicin) were not formed below pH 3.6, thus alliinase is completely and irreversibly inhibited by stomach acid. A second (unidentified) enzyme, in addition to alliinase is involved in thiosulfinate formation. A stomach acid-resistant coating on garlic powder tablets is necessary for thiosulfinate release, which if prepared carefiilly can release amounts of total thiosulfinates similar to whole garlic cloves. ... 

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