Histamine analogues: imidazolylalkylguanidines, synthesis and in vitro pharmacology

Impromidine analogues characterized by modified side chains connecting the guanidine and imidazole moieties have been prepared and tested for H2-agonistic activity on isolated guinea-pig right atrium and for H1-antagonistic activity on guinea-pig ileum, respectively. 3-(1H-Imidazol-4-yl)propylguanidines with varied cimetidine-like side chain (5a–d) proved to be almost full H2-agonists and 5–70 times more potent than histamine, whereas compounds with β- or γ-methyl branched imidazolylpropyl moiety (5e, 5f, 5h) are only weak partial H2-agonists. Both unsaturated impromidine analogues (5i, 5j) are full H2-agonists, the (Z)-configurated compound 5j being about 4 times more potent than the (E)-configurated derivate 5i.