Role of Hydrophobic Substituents on the Terminal Nitrogen of Histamine in Receptor Binding and Agonist Activity: Development of an Orally Active Histamine Type 3 Receptor Agonist and Evaluation of Its Antistress Activity in Mice

The terminal nitrogen atom of histamine was modified with lipophilic substituents to investigate the structure−activity relationship of histamine type 3 receptor (H3R) agonists. The introduction of an alkylated benzene rings maintained or increased the H3R binding affinity. The most potent compound, 4-(2-(4-tert-butylphenylthio)ethyl)-1H-imidazole, possessed in vivo agonistic activity, decreasing brain N^τ-methylhistamine levels in mice after oral administration. It also exhibited antistress activity in the mouse resident−intruder test.