This ErbB1/2 inhibitor (FW = 466.94 g/mol; CAS 845272-21-1), also named (R)-N4 -(3-chloro-4-(thiazol-2-ylmethoxy)phenyl)-N6 -(4-methyl-4,5- dihydrooxazol-2-yl)quinazoline-4,6-diamine, selectively targets the intrinsic protein kinase activities of ErbB1, or Epidermal Growth Factor Receptor (EGFR), IC50 = 7 nM and ErbB2, or Human Epidermal growth factor Receptor (HER2), IC50 = 2 nM. ARRY-334543 also reverses multidrug resistance by antagonizing the activity of ATP-binding cassette subfamily G member 2.