(3R,4S)-Tofacitinib-d3 is the labeled analogue of (3R,4S)-Tofacitinib (T528000), an enantiopure stereoisomer of the drug, Janus kinase 3(Jak3) inhibitor (CP-690,550) that has been found to inhibit selected members of the STE7 and STE20 subfamily of kinases.