As a continuation of previous research on anticholinergic drugs derived from 2,2-diphenyl-2-ethylthioacetic acid, several 5,5-diphenyl-5-ethylthio-2-pentynamines ( 2 – 11 ) were synthetised and their antimuscarinic activity on M 1–4 receptor subtypes was evaluated by functional tests and binding experiments. One of the compounds obtained showed unexpected agonistic activity in functional experiments on M 2 receptors. Since the compound carried a phenylpiperazine moiety, other similar compounds ( 12 – 17 ) were prepared and found to be endowed with similar behaviour. These ligands, although possessing the bulky structure characterising muscarinic antagonists, display agonistic activity at M 2 subtypes while, as expected, behaving as antagonists on M 3 and M 4 subtypes. On M 1 subtypes, they show agonistic activity which, however, is not blocked by atropine. The peculiar pharmacological profile of these compounds is of interest for studying muscarinic receptor subtypes.
