A class of rigid, dibasic, non-imidazole H-3 antagonists was developed, starting from a series of previously described flexible compounds. The original polymethylene chain between two tertiary amine groups was replaced by a rigid scaffold, composed by a phenyl ring or a biphenyl fragment. Modulation of the distance between the two amine groups, and of their alkyl substituents, was driven by superposition of molecular models and docking into a receptor model, resulting in the identification of 1,1'-[biphenyl-4,4'diylbis(methylene)]bis-piperidine (5) as a subtype-selective H-3 antagonist with high binding affinity (pK(i) = 9.47) at human H-3 histamine receptor. (c) 2006 Elsevier Ltd. All rights reserved.