A potent and covalent BTK inhibitor (IC50 = 0.3 nM); selective for BTK over a panel of 304 kinases at 1 μM; inhibits EGFR, Tec, Blk, BMX, HER4, and TXK (IC50s = 0.62-33 nM); inhibits phosphorylation of BTK at Y233 (IC50 = 1.8 nM) in Ramos cells; reduces viability of REC-1 cells (IC50 = 0.36 nM); reduces tumor volume in an OCI-LY10 DLBCL mouse xenograft model at 2.5 and 7.5 mg/kg