Agonistic and antagonistic bivalent ligands for serotonin and dopamine receptors including their transporters

This review deals with the literature (1982-2006) concerning bivalent ligands for dopamine (D) and serotonin (5-HT) receptors, as well as for their respective transporters. The design, synthesis, and pharmacological evaluation of bivalent agonists and antagonists for dopamine and serotonin receptors have been successfully pursued. Increased potencies for 5-HT1B/1D receptor agonists were achieved as well as improved selectivities. At these receptors, selectivity seems to depend strongly on spacer length, whereas the improved affinities seem to be based on the presence of two pharmacophores within one molecule. Intrinsic activities and pharmacokinetic properties may differ from those of the respective monovalent ligands. Additionally, improved central nervous system penetration was achieved. Bivalent dopamine receptor agonists and antagonists can exhibit selectivity profiles different from their monomeric analogues with no loss in potency. For dopamine antagonists, affinities depend strongly on spacer length. For agonistic dimers different pharmacokinetic properties were observed. Bivalency was also applied to inhibitors of monoamine re-uptake transporters. Selectivity profiles and affinities depend strongly on the length of the alkylene-spacer: For some dimeric inhibitors the norepinephrine transporter (NET) and the dopamine transporter (DAT) affinities changed gradually, but for the serotonin transporter (SERT) a pentamethylene spacer showed the highest potency. Because the bivalent ligand approach has just begun to be applied to these versatile, therapeutically important targets, many advances in affinity enhancement, as well as the achievement of novel selectivity profiles and improved pharmacokinetics can be expected.