[Isohistamine and homologs as components of H2-antagonists. 22. H2-antihistaminics].

Starting with isohistamines and their homologues or from appropriately hydrogenated imidazo[1,2-c]pyrimidines, imidazo[1,2-c] [1,3]diazepines and -diazocines, H2-antihistaminics with cyanoguanidine and 2-nitro-1,1-ethenediamine structure were prepared and tested for their H2-antagonistic activity on the isolated guinea-pig atrium and on the histamine-stimulated acid secretion of the anaesthetized rat. While the cyanoguanidines 3a-c,f were weaker in comparison to cimetidine, or inactive, 12a-e,g-l, 17 and 19 possessed markedly stronger activity, whereby the activity reaches a maximal effect at the rat stomach when cyanoguanidine and imidazole ring are connected with a three-membered chain. The activity of the 2-nitro-1,1-ethenediamines 15b,h,l exceed that of the comparable cyanoguanidines at both test models.