Identification of 4-(1H-imidazol-4(5)-ylmethyl)pyridine (immethridine) as a novel, potent, and highly selective histamine H(3) receptor agonist.

In this study, the piperidine ring of immepip and its analogues was replaced by a rigid heterocyclic pyridine ring. Many compounds in the series exhibit high affinity and agonist activity at the human histamine H 3 receptor. Particularly, the 4-pyridinyl analogue of immepip (1c, immethridine) is identified as a novel potent and highly selective histamine H 3 receptor agonist (pK, = 9.07, pEC 50 = 9.74) with a 300-fold selectivity over the closely related H 4 receptor.