BLK-IN-2 (compound 25) is a potent and selective irreversible inhibitor of B-Lymphoid tyrosine kinase (BLK), with an IC50 of 5.9 nM. BLK-IN-2 also inhibits BTK (IC50=202.0 nM). BLK-IN-2 shows potent antiproliferative activities against several lymphoma cells.