Substituted conformationally restricted guanidine derivatives: Probing the α2-adrenoceptors' binding pocket.In this paper we report the design, synthesis and pharmacological evaluation of new N-substituted 2-amino-1,4-dihydroquinazolines, 2-amino-1,4-dihydropyridopyrimidines and 2-amino-4,5-dihydro-1,3-benzodiazepines as α2-adrenoceptors ligands.  Computational studies show that the proposed substitutions and guanidine-containing ring size will probe an extensive area of the active site.  Preparation of these molecules involved novel routes than those previously utilised in our laboratory for the preparation of the acyclic aryl-guanidine counterparts.  Compounds 8b and 18c showed the highest affinity and antagonistic activity, within their series, towards the α2-adrenoceptor in human brain tissue in vitro experiments.  Structure-activity relationships have been established for the design and biological evaluation of novel α2-adrenoceptor ligands.
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