Weak histamine H₂-receptor blocking activity of ranitidine analogues containing conformationally restricted connecting chains

The paper describes the activity of ranitidine analogues in which a rigid molecular conformation has been attained by the substitution of the flexible connecting chain with an o-phenylene unit. The results indicate that this structural manipulation causes a dramatic decrease of H₂-blocking activity. It is concluded that the introduction of the o-phenylene imposes a geometrical constraint which results in a refolded molecular conformation.