We have designed and synthesized a new series of arylpiperazines V exhibiting high 5-HT1AR affinity and selectivity over α1-adrenoceptors. The new selective 5-HT1AR ligands contain a hydantoin (m = 0) or diketopiperazine (m = 1) moiety and an arylpiperazine moiety separated by one methylene unit (n = 1). The aryl substituent of the piperazine moiety (Ar) consists of different benzofused rings mimicking the favorable voluminous substituents at ortho and meta positions predicted by 3D-QSAR analysis in the previously reported series I. In particular, (S)-2-[[4-(naphth-1-yl)piperazin-1-yl]methyl]-1,4-dioxoperhydropyrrolo[1,2-a]pyrazine [(S)-9, CSP-2503] (5-HT1A, Ki = 4.1 nM; α1, Ki > 1000 nM) has been pharmacologically characterized as a 5-HT1AR agonist at somatodendritic and postsynaptic sites, endowed with anxiolytic properties. Ligand (S)-9 is predicted, in computer simulations, to bind Asp3.32 in TMH 3, Thr5.39 and Ser5.42 in TMH 5, and Trp6.48 in TMH 6. We propose that agonists modify, by means of an exp...