Mer kinase inhibitor design. (A) General structure of pyrazolopyrimidine template designed for Mer kinase inhibition. R¹, R², and R³ represent substituents that can be synthetically varied to optimize the biological properties of this template. (B) X-ray cocrystal structure (PDB 3TCP) of UNC569 and the Mer kinase catalytic domain illustrating the binding mode and location of R¹, R², and R³ in the enzyme active site. (C) Structure and inhibitory properties of UNC1062 versus the TAM family kinases.