A series of piperazin-1-yl substituted unfused heterobiaryls was synthesized as ligands of the 5-HT7 receptors. The goal of this project was to elucidate the structural features that affect the 5-HT7 binding affinity of this class of compounds represented by the model ligand 4-(3-furyl)-2-(4-methylpiperazin-1-yl)pyrimidine (2). The SAR studies included systematical structural changes of the pyrimidine