L-Kynurenine ((S)-Kynurenine) is a key intermediate in the breakdown pathway of tryptophan. L-Kynurenine is a substrate of kynureninase, KMO, and KAT associated with the suppression of antitumor immune responses. It has been shown to inhibit allogeneic T-cell proliferation and to increase malignant U87 glioma cell invasion into a collagen matrix.

D-Kynurenine (ZINC901103) is a metabolite of D-tryptophan and an agonist of GPR109B. D-Kynurenine activates AhR and promotes the conversion of the epithelium to mesenchyme. D-Kynurenine serves as a substrate in the fluorescence analysis of D-amino acid oxidase.

2-Amino-4-(2-aminophenyl)-4-oxobutanoic acid is a ketone and amino acid derivative with a variety of biological functions including vasodilatory, immunomodulatory, and neuromodulatory activities.2-Amino-4-(2-aminophenyl)-4-oxobutanoic acid is the precursor of niacin. 2-Amino-4-(2-aminophenyl)-4-oxobutanoic acid is the precursor of nicotinic acid. Abnormal production of 2-Amino-4-(2-aminophenyl)-4-oxobutanoic acid has been linked to cognitive deficits and depressive symptoms associated with neurological disorders. 2-Amino-4-(2-aminophenyl)-4-oxobutanoic acid is overexpressed in certain types of cancer cells and may be used to assess cancer risk. Expressed and may be used as a biomarker for assessing cancer risk.