S-Methylcysteine sulfoxide

S-Methylcysteine sulfoxide is an organosulfur compound with the formula CH₃S(O)CH₂CH(NH₂)CO₂H. It is the sulfoxide of S-methylcysteine. It contributes to the flavor of onions (Allium sp.).^[1][2] The compound is usually encountered as one diastereoisomer, the (R)- and (S)-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.

Quick facts Names, Identifiers ...

S-Methylcysteine sulfoxide

Names
IUPAC name 2-Amino-3-methylsulfinylpropanoic acid
Other names methiin, S-methyl-L-cysteine oxide,
Identifiers
CAS Number	4740-94-7 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:137271
ChemSpider	74136
PubChem CID	82142
CompTox Dashboard (EPA)	DTXSID70963830
InChI InChI=1S/C4H9NO3S/c1-9(8)2-3(5)4(6)7/h3H,2,5H2,1H3,(H,6,7) Key: ZZLHPCSGGOGHFW-UHFFFAOYSA-N
SMILES CS(=O)CC(C(=O)O)N
Properties
Chemical formula	C4H9NO3S
Molar mass	151.18 g·mol−1
Appearance	White solid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

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S-Methylcysteine sulfoxide is produced from glutathione.^[3]

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.^[3]