R406 is an orally available and competitive Syk/FLT3 inhibitor for ATP binding with a Ki of 30 nM, potently inhibits Syk kinase activity in vitro with an IC50 of 41 nM, measured at an ATP concentration corresponding to its Km value. R406 reduces immune complex-mediated inflammation. R406 also inhibits Lyn (IC50=63 nM) and Lck (IC50=37 nM).