Diaminopyrimidines, diaminopyridines and diaminopyridazines as histamine H4 receptor modulators.

Previously disclosed H4 receptor modulators, the triamino substituted pyridines and pyrimidines, contain a free primary amino (-NH2) group. In this Letter we demonstrate that an exocyclic amine (NH2) is not needed to maintain affinity, and also show a significant divergence in the SAR of the pendant diamine component. These des-NH2 azacycles also show a distinct functional spectrum, that appears to be influenced by the diamine component; in the case of the 1,3-amino pyrimidines, the preferred diamine is the amino pyrrolidine instead of the more common piperazines. Finally, we introduce 3,5-diamino pyridazines as novel histamine H4 antagonists.