The human histamine H4 receptor (hH4R) is a promising new target in the therapy of inflammatory diseases and disorders of the immune system. For the development of new H4R antagonists a broad ligand-based virtual screening was performed resulting in two hits. The dissection of their common annelated aromatic core into its heteromonocyclic components showed that 2, 4-diaminopyrimidine is a potent hH4R affinity scaffold, which ...