Аллицин

АЛЛИЦИН— органическое анти­биотическое вещество, структурной формулы:

CJI, = СН — СИ, — S СН, = СН — СИ, — S4

I ИЛИ \ О.

СП, = C1I — СН, — S-f — о— СП, = СН — си, —ъ/

Бесцветная маслянистая жидкость, плохо рас­творяющаяся в воде и хорошо в обычных органич. растворителчх, плотность 1,109. А. неустойчив, особенно в водных растворах, при хранении по- лимеризуется, разрушается щелочами \же на холоду, обладает антибактериальной активностью против ряда микроор! анизмов. Получается из чес­нока, а также может быть получен синтетически окислением диаллилдисульфида.

Лит.: Шемякин М. М. и X о х л о в а А. С., Химия антибиотических мешестп. М.—Л.. 1 949.

Аллици́н — химич. соединение, образующееся при механическом разрушении клеток чеснока, обладающее бактерицидным и фунгицидным действием.

Не присутствует в чесноке, а образуется из своего предшественника - аминокислоты аллиина. В целом зубке аллиин и фермент аллициназа разделены: фермент — находится в вакуолях, а аллиин — в цитоплазме. При нарушении целостности зубка клетки его разрушаются и их компоненты вступают во взаимодействие, при этом образуется А.

А. — соединение с невысокой термической стабильностью. Он медленно разрушается при комнатной температуре и быстро — при нагревании (готовке).

Острый, жгучий вкус свежего чеснока также обусловлен А.

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

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

(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. Furthermore, allicin can be unstable, breaking down within 16 h at 23 °C.  

Several animal studies published between 1995 and 2005 indicate that allicin may: reduce atherosclerosis and fat deposition,  normalize the lipoproteinbalance, decrease blood pressure,  have anti-thrombotic  and anti-inflammatory activities, and function as an antioxidant to some extent. Other studies have shown a strong oxidative effect in the gut that can damage intestinal cells.  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.  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.  The 2-propenesulfenic formed when garlic is cut or crushed has a lifetime of less than one second. 

Allicin has been found to have numerous antimicrobial properties, and has been studied in relation to both its effects and its biochemical interactions. 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. 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. 

A water-based formulation of purified allicin was found to be more chemically stable than other preparations of garlic extracts. 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.  (Presumably, the dilution of these components in water helps to preserve the allicin molecule.)