ISOTHIOUREA ANALOGS OF HISTAMINE AS POTENT AGONISTS OR ANTAGONISTS OF THE HISTAMINE H-3 RECEPTOR

The synthesis and H-3-activity of a series of isothiourea analogues of histamine have been described. It has been shown that S-[2-(4(5)-imidazolyl)ethylisothiourea (VUF 8325) is a potent H-3-agonist measured as the electrically evoked contraction of the guinea-pig ileum. Upon methylation of the imidazole system or the isothiourea moiety a decrease in affinity was observed leading to either weak agonists or weak antagonists. Introduction of N-(phenylalkyl) substituents at the isothiourea part gives rise to highly potent H-3-antagonists. Particularly the 4-chlorobenzyl group appeared to be favourable in the series described resulting in a histamine H-3-antagonist with a pA2-value of 9.9.