Quinolinic acid is an endogenous N-methyl-D-aspartate receptor agonist synthesized from L-tryptophan via the kynurenine pathway and thereby has the potential of mediating N-methyl-D-aspartate neuronal damage and dysfunction. Elevated cerebrospinal fluid levels of quinolinic acid are correlated with the severity of neuropsychological deficits in patients who have AIDS. It can act as an endogenous brain excitotoxin when released by activated macrophages. Quinolinic acid is being used as a research tool to examine the role of excitotoxicity in neuronal degeneration associated with a number of neurological diseases (Alzheimer's disease, Huntington's disease, Parkinson's disease) which involve selective neurotransmitter deficits.

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.