Potent, ATP-competitive inhibitor of Clk-family kinases (IC50 values are 15, 20 and 200 nM for mClk4, 1 and 2 respectively and >10 μM for mClk3). Also inhibits DYRK1A/B (IC50 values are 24 and 34 nM respectively). Suppresses serine/arginine-rich protein phosphorylation; affects the regulation of alternative splicing by phosphorylation of SR protein both in vitro and in vivo. Purity 98%. MW (observed): 249.33