Methionine sulfone (CAS: 820-10-0), also known as L-methionine-S-dioxide, belongs to the class of organic compounds known as L-alpha-amino acids. These are alpha-amino acids which have the L-configuration at the alpha-carbon atom. Methionine sulfone is a very strong basic compound (based on its pKa). Methionine sulfone has been detected, but not quantified, in garden onions.