Synthesis and structure-activity relationships of dual histamine H2 and gastrin receptor antagonists with noncyclic gastrin receptor antagonistic moieties.

In order to study structure-activity relationships of dual histamine H2 and gastrin receptor antagonists as well as to improve their low oral absorbability, their prototype benzodiazepine gastrin receptor antagonistic moieties were altered to a conformationally flexible noncyclic dipeptide equivalent. This skeletal modification significantly potentiated the binding affinity of hybrid compounds for the histamine H2 receptor, whereas their affinity for the gastrin receptor and receptor selectivity over the CCK-A receptor varied widely with the substituents on the gastrin moiety. Among them, [3-[3-(3-piperidin-1-ylmethylphenoxy)propylcarbamoyl]p ropyl carbamic acid 3-[3-([(3-methoxyphenyl)[(methylphenylcarbamyl)methyl]carbamoyl]me thyl)ureido]benzyl ester (7a) showed the highest dual histamine H2 and gastrin receptor antagonistic activities. It also displayed distinct gastric acid antisecretory activity in vivo for two assays, namely, Schild's rat method by i.d. administration and the rat pylorus ligation method by oral administration. With the latter case, dose-response relationships were observed for the first time, suggesting its substantially improved oral absorbability. However, 7a did not display distinct in vivo gastric acid antisecretory activity for the assay with Heidenhain pouch dogs.