The influence of guanidino and isothiourea groups in histaminergic compounds on H2-activity

Because in some alkylenediisothioureas replacement of one of the isothiourea groups by a guanidino group resulted in a strong increase in agonistic histamine H2-activity, while replacement of the guanidino group of a potent analogue of impromidine by an isothiourea group resulted in a complete loss of histamine H2-activity, it was concluded that guanidino and isothiourea groups are not bio-isosteric for the H2-receptor.