Used as a key intermediate in tryptophan metabolism studies, particularly in research related to the kynurenine pathway. It serves as a biomarker for immune activation and inflammation, especially in neurological and psychiatric disorders such as depression, schizophrenia, and neurodegenerative diseases. Applied in biochemical assays to monitor enzyme activity, including indoleamine 2,3-dioxygenase (IDO) and tryptophan 2,3-dioxygenase (TDO), which are targets in cancer immunotherapy and inflammatory disease research. Also utilized in metabolomics studies to understand cellular immune responses and in drug development for modulating immune tolerance.