2-Cyclohexyl-1-(5H-imidazo[5,1-a]isoindol-5-yl)ethanoned-d10 is an intermediate used in the synthesis of NLG919-d10 (N630002), which is the isotope labelled analog of NLG919 (N630000). NLG919 is a potent indoleamine-2,3-dioxygenase (IDO) pathway inhibitor and is suitable for the treatment of immunosuppression associated with cancer.