UNC2881 is an inhibitor of Mer (IC50 = 4.3 nM), a member of the TAM family of receptor tyrosine kinases. It is selective for Mer over the remaining TAM family members Axl and TYRO3 (IC50s = 360 and 250 nM, respectively). UNC2881 inhibits phosphorylation of Mer in 697 B-ALL acute lymphoblastic leukemia cells (IC50 = 21.9 nM). It inhibits platelet aggregation and ATP release induced by type I equine fibrillar collagen in isolated human platelet-rich plasma when used at a concentration of 3 μM.