Potent and selective inhibitor of Bruton's tyrosine kinase (BTK). Inhibits recombinant BTK with an IC50 value of 2.5 μM and has no activity on other protein kinases ( including JAK1, JAK3, HCK, EGFR kinase and insulin receptor kinase) at concentrations of up to 278 μM. Purity 98%. MW (observed): 360