(a) The chemical structure of cyclofenilacrylic acid-based bivalent ligand AK-15b. (b) The chemical structures of SR141617A, PPHT, the initially designed CBR1-D2R bivalent ligands and SAR explorations derived from SR141617A. (c) The chemical structure of the MOR-CCR5 bivalent ligand VZMC001. (d) The chemical structures of eticlopride, NT(8–13) and designed D2R–NTS1R bivalent ligands, (e) The chemical structures of MTEP, DAPT, DAP, linkers and mGluR5–D2R bivalent ligand MQ-22a.