D-amino acid homopiperazine amides: discovery of A-320436, a potent and selective non-imidazole histamine H(3)-receptor antagonist.

Structure-activity relationships of homopiperazine-containing alkoxybiaryl nitriles employing various D-amino acid moieties and their N-furanoyl analogues were undertaken. This led to A-320436, a potent and selective non-imidazole H(3)-receptor antagonist possessing balanced affinity for both rat and human H(3)-receptors. This compound was shown to demonstrate in vitro and in vivo functional antagonism and is non-neurotoxic at doses (i.p.) up to 163 mg/kg in a general observation test.