A thiomalic acid or mercaptosuccinic acid is a dicarboxylic acid containing a thiol functional group. Mercaptosuccinic acid is used in the preparation of mercaptosuccinic acid diethyl ester by reaction with ethanol. It is also used as a brightening agent in metal plating. Further, it serves as an intermediate for the synthesis of corrosion inhibitors, soil fumigants, active pharmaceutical ingredients and electroplating agents. Mercaptosuccinic acid is widely used in the synthesis of various biologically active sulfur containing compounds such as the antileukemic spiro[indoline-3,2'-thiazolidine]-2,4'-diones, and the antimicrobial and antitubercular 4-thiazolidinones. It is also used as a building block in the synthesis of novel polyanionic inhibitors of human immunodeficiency virus and other viruses, and as a starting material in the synthesis of isocysteine, an important non-proteinogenic amino acid in a potent peptide inhibitor of stromelysin. In addition, sodium salt of the anionic Au(I) complex of 2-mercaptosuccinic acid is an effective antiarthritic drug.

Phosphamidon is an organophosphorus insecticide widely used in agriculture, which consists of two isomers Z and E. Phosphamidon is highly toxic to mammals and was shown to inhibit acetylcholinesterase in the brain of the hen.