Heterocyclic Replacement of the Central Phenyl Core of Diamine-Based Histamine H3 Receptor Antagonists.

A series of small molecules consisting of a heterocyclic core flanked by two basic functionalities were synthesized and screened for in vitro affinity at the human histamine H(3) receptor (hH(3)R). Nine of the twenty-eight compounds tested were found to possess a hH(3)R K(i) of less than 5 nM and consisted of a diverse range of central hetero-aromatic linkers (pyridine, pyrazine, oxazole, isoxazole, thiazole, furan, thiophene, and pyrrole). One member of this series, (4-isopropyl-piperazin-1-yl)-(6-piperidin-1-ylmethyl-pyridin-3-yl)-methanone (37), was found to be a high affinity, selective antagonist that crosses the blood-brain barrier and occupies H(3) receptors after oral administration in the rat.