TCS 21311 is a potent and selective JAK3 inhibitor with the IC50 values of 8 nM. TCS 21311 shows high selectivity for JAK3 over JAK1, JAK2 and TYK2. The IC50 values are 1017, 2550 and 8055 nM respectively. TCS 21311 exihibits inhibitory effect on GSK-3β, PKCα and PKCθ with the IC50 values of 3, 13 and 68 nM, respectively [1].

Janus kinases (JAK) belong to a small family of cytoplasmic protein tyrosine kinases including JAK1, JAK2, Tyk2, and JAK3, which play important roles in initiating the cytokine-triggered signaling events by activators of transcription (STAT) proteins via tyrosine phosphorylation [2]. Due to its association with relevant cytokine signaling pathways, JAK3 serves as an important target for therapeutic intervention in the treatment of inflammatory diseases, autoimmune disorders and organ transplant rejection [2].

References:
[1] Thoma G, Nuninger F, Falchetto R, et al.  Identification of a potent Janus kinase 3 inhibitor with high selectivity within the Janus kinase family[J]. Journal of medicinal chemistry, 2010, 54(1): 284-288.
[2] Clark M P, George K M, Bookland R G, et al.  Development of new pyrrolopyrimidine-based inhibitors of Janus kinase 3 (JAK3)[J]. Bioorganic & medicinal chemistry letters, 2007, 17(5): 1250-1253.