A cell-permeable, potent, and reversible inhibitor of Janus kinase 3 (JAK3) (IC50 = 27 nM). Reported to bind to the enzyme active site and prevent IL-2-induced phosphorylation of JAK3 and STAT5. Also reported to inhibit IL-2-induced cell proliferation (IC50 = 760 nM for murine CTLL cells and 250 nM for human T-cells). Shown to alleviate oxazolone-induced ear edema in mice with an efficacy comparable to Dexamethasone (Cat. No. 265005) and displays ~16-fold greater selectivity over JAK2.