1-Methyltryptophan is a chemical compound that is an inhibitor of the tryptophan catabolic enzyme indoleamine 2,3-dioxygenase (IDO or INDO EC 1.13.11.52). It is a chiral compound that can exist as both D- and L-enantiomers. The L-isomer (L-1MT) inhibits IDO weakly but also serves as an enzyme substrate. A U.S. patent covering salt and prodrug formulations of indoximod was issued to NewLink Genetics on August 15, 2017 providing exclusivity until at least 2036.