Azines and Diazines as Potential Histamine H 3 ‐Receptor Antagonists

In search of structure‐activity relationships among histamine H 3 ‐receptor antagonists the imidazole ring of known H 3 ‐receptor antagonists was replaced by different heteroaromatic ring systems. Thus, azines and diazines with ether ( 6 – 13 ) and carbamate ( 15 – 24 ) moieties as functional groups were synthesized. The obtained compounds did not show significant H 3 ‐receptor antagonist activity in vitro (rat brain cortex) or in vivo (mice brain). The new compounds were also screened for H 1 ‐receptor antagonist activity on the isolated guinea‐pig ileum and for H 2 ‐receptor antagonist activity on the isolated spontaneously beating guinea‐pig right atrium. The substances showed only weak antagonistic activity at both histamine receptors, H 1 and H 2 .