S-Methylcysteine sulfoxide
S-Methylcysteine sulfoxide is an organosulfur compound with the formula. It is the sulfoxide of S-methylcysteine. It contributes to the flavor of onions. The compound is usually encountered as one diastereoisomer, the - and -configurations at the carbon and sulfur stereocenters, respectively. The S-methyl part of the name refers to the location of the methyl group on sulfur. Although odorless, S-methylcysteine sulfoxide is acted upon by alliinase and lachrymatory-factor synthase.
S-Methylcysteine sulfoxide is produced from glutathione.
Related compounds are the unsaturated sulfoxides S-''trans-prop-1-enyl cysteine sulfoxide and S''-propyl cysteine sulfoxide, both found also in onions, and S-allyl cysteine sulfoxide, typically found in garlic.