Alliin


Alliin is a sulfoxide that is a natural constituent of fresh garlic. It is a derivative of the amino acid cysteine. When fresh garlic is chopped or crushed, the enzyme alliinase converts alliin into allicin, which is responsible for the aroma of fresh garlic.
Garlic has been used since antiquity as a therapeutic remedy for certain conditions now associated with oxygen toxicity, and, when this was investigated, garlic did indeed show strong antioxidant and hydroxyl radical-scavenging properties, it is presumed owing to the alliin contained within. Alliin has also been found to affect immune responses in blood.
Alliin was the first natural product found to have both carbon- and sulfur-centered stereochemistry.

Chemical synthesis

The first reported synthesis, by Stoll and Seebeck in 1951, begins the alkylation of L-cysteine with allyl bromide to form deoxyalliin. Oxidation of this sulfide with hydrogen peroxide gives both diastereomers of L-alliin, differing in the orientation of the oxygen atom on the sulfur stereocenter.
A newer route, reported by Koch and Keusgen in 1998, allows stereospecific oxidation using conditions similar to the Sharpless asymmetric epoxidation. The chiral catalyst is produced from diethyl tartrate and titanium isopropoxide.