Selective inhibitor of the bone morphogenic protein (BMP) ALK2 receptor (IC50 = 108 nM). Exhibits no detectable inhibition of AMPK, ALK5, KDR (VEGFR-2) or PDGFRβ receptors. Blocks BMP4-induced phosphorylation of Smads 1, 5 and 8 in HEK293 cells.