[show abstract][hide abstract] ABSTRACT: Two series of triamino pyrimidines and a series of triamino pyridines have been synthesized and their structure-activity relationships evaluated for activity at the H(4) receptor in competitive binding and functional assays. Small structural changes in these three hetereoaromatic cores influenced the functional activity of these compounds.
[show abstract][hide abstract] ABSTRACT: The present work details the transformation of a series of human histamine H(4) agonists into potent functional antagonists. Replacement of the aminopyrrolidine diamine functionality with a 5,6-fused pyrrolopiperidine ring system led to an antagonist. The dissection of this fused diamine led to the eventual replacement with heterocycles. The incorporation of histamine as the terminal amine led to a very potent and selective histamine H(4) agonist; whereas incorporation of the constrained histamine analog, spinacamine, modulated the functional activity to give a partial agonist. In two separate series, we demonstrate that constraining the terminal amino portion modulated the spectrum of functional activity of histamine H(4) ligands.
[show abstract][hide abstract] ABSTRACT: The histamine H(4) receptor (H(4)R) is the latest identified histamine receptor to emerge as a potential drug target for inflammatory diseases. Animal models are employed to validate this potential drug target. Concomitantly, various H(4)R orthologs have been cloned, including the human, mouse, rat, guinea pig, monkey, pig, and dog H(4)Rs. In this article, we expressed all these H(4)R orthologs in human embryonic kidney 293T cells and compared their interactions with currently used standard H(4)R ligands, including the H(4)R agonists histamine, 4-methylhistamine, guanidinylethyl isothiourea (VUF 8430), the H(4)R antagonists 1-[(5-chloro-1H-indol-2-yl)carbonyl]-4-methylpiperazine (JNJ 7777120) and [(5-chloro-1H-benzimidazol-2-yl)carbonyl]-4-methylpiperazine (VUF 6002), and the inverse H(4)R agonist thioperamide. Most of the evaluated ligands display significantly different affinities at the different H(4)R orthologs. These "natural mutants" of H(4)R were used to study ligand-receptor interactions by using chimeric human-pig-human and pig-human-pig H(4)R proteins and site-directed mutagenesis. Our results are a useful reference for ligand selection for studies in animal models of diseases and offer new insights in the understanding of H(4)R-ligand receptor interactions.