A novel hybrid bioisostere generation/virtual screening method combined with narrowing of chemical space through similarity to compounds that are active at the second target was successfully applied for the development of structurally new dual 5-HT6/D2 receptor ligands. Consequently, a series of derivatives of the found hit 1d (N-[2-(dimethylamino)ethyl]-N-(2-phenylethyl)aniline) was synthesized. The most active 5-HT6/D2 ligands also showed affinity for 5-HT7R and 5-HT2R. The parachloroaniline derivative was identified as a potent dual 5-HT6/5-HT7 receptor antagonist (Ki=24 nM and Kb=30 nM, Ki=4 nM and Kb=1.4 nM, respectively). In the case of halogen-containing compounds, interesting structure-activity relationships were observed at 5-HT6, D2 and 5-HT7 receptors, and the ligand-receptor complexes were subsequently examined using a molecular modelling approach that combined quantum-polarized ligand docking (QPLD) and Molecular-Mechanics-Generalized-Born/Surface Area (MM/GBSA) free-energy calculation, which permitted the identification of putative halogen binding pockets.

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