Cowart et al (2008) Rotationally constrained 2,4-diamino-5,6-disubstituted pyrimidines: a new class of histamine H4 receptor antagonists with improved druglikeness and in vivo efficacy in pain and inflammation models. J.Med.Chem. 51 6547. Leurs et al (2009) Molecular and biochemical pharmacology of the histamine H4 receptor. Br.J.Pharmacol. 157 14.