The Versatile 2-Substituted Imidazoline Nucleus as a Structural Motif of Ligands Directed to the Serotonin 5-HT1A Receptor

The involvement of the serotonin 5-HT1A receptor (5-HT1A-R) in the antidepressant effect of allyphenyline and its analogues indicates that ligands bearing the 2-substituted imidazoline nucleus as a structural motif interact with 5-HT1A-R. Therefore, we examined the 5-HT1A-R profile of several imidazoline molecules endowed with a common scaffold consisting of an aromatic moiety linked to the 2-position of an imidazoline nucleus by a biatomic bridge. Our aim was to discover other ligands targeting 5-HT1A-R and to identify the structural features favoring 5-HT1A-R interaction. Structure–activity relationships, supported by modeling studies, suggested that some structural cliché such as a polar function and a methyl group in the bridge, as well as proper steric hindrance in the aromatic area of the above scaffold, favored 5-HT1A-R recognition and activation. We also highlighted the potent antidepressant-like effect (mouse forced swimming test) of (S)-(+)-19 [(S)-(+)-naphtyline] at very low dose (0.01 mg kg−1). This effect was clearly mediated by 5-HT1A, as it was significantly reduced by pretreatment with the 5-HT1A antagonist WAY100635.