Alliinase

In garlic, an alliinase enzyme acts on the chemical alliin converting it into allicin.

[2] However, the sulfenic acid intermediate is not chiral, and the final product's stereochemistry is not controlled.

There are a range of similar enzymes that can react with the cysteine-derived sulfoxides present in different species.

A separate enzyme, the lachrymatory factor synthase or LFS, then converts this chemical to syn-propanethial-S-oxide, a potent lachrymator.

The analogous butyl compound, syn-butanethial-S-oxide, is found in Allium siculum species.