Guanidine-based α2-adrenoceptor ligands: Towards selective antagonist activity

Depression has been linked to a selective increase in the high affinity conformation of the alpha(2)-adrenergic autoreceptors (alpha 2-ARs) in the human brain as well as to an overexpression of alpha 2-ARs in the hippocampus and cerebral cortex. Thus, the development of novel alpha 2-AR antagonists represents an attractive source of new antidepressants. This paper describes the design, synthesis and pharmacological evaluation of 30 new guanidinium and 2-iminoimidazolidinium as potential alpha 2-AR antagonists. In order to design this new series of alpha 2-AR antagonists, a pharmacophore model was developed using the GALAHAD software. This study suggested that increased substitution in the space surrounding the cationic guanidine moiety might lead selectively to antagonist activity. Following the preparation of compounds incorporating this feature and competitive radioligand binding, [S-35]GTP gamma S functional assays revealed that this structural modification affords exclusively alpha 2-AR antagonists, in contrast with the analogous unsubstituted compounds in which a mixture of antagonist/agonist activities was previously observed. (C) 2014 Elsevier Masson SAS. All rights reserved.