Carbazole and tetrahydro-carboline derivatives as dopamine D₃ receptor antagonists with the multiple antipsychotic-like properties

Dopamine D₃ receptor (D₃R) is implicated in multiple psychotic symptoms. Increasing the D₃R selectivity over dopamine D₂ receptor (D₂R) would facilitate the antipsychotic treatments. Herein, novel carbazole and tetrahydro-carboline derivatives were reported as D₃R selective ligands. Through a structure-based virtual screen, ZLG-25 (D₃R K_i = 685 nmol/L; D₂R K_i > 10,000 nmol/L) was identified as a novel D₃R selective bitopic ligand with a carbazole scaffold. Scaffolds hopping led to the discovery of novel D₃R-selective analogs with tetrahydro-β-carboline or tetrahydro-γ-carboline core. Further functional studies showed that most derivatives acted as hD₃R-selective antagonists. Several lead compounds could dose-dependently inhibit the MK-801-induced hyperactivity. Additional investigation revealed that 23j and 36b could decrease the apomorphine-induced climbing without cataleptic reaction. Furthermore, 36b demonstrated unusual antidepressant-like activity in the forced swimming tests and the tail suspension tests, and alleviated the MK-801-induced disruption of novel object recognition in mice. Additionally, preliminary studies confirmed the favorable PK/PD profiles, no weight gain and limited serum prolactin levels in mice. These results revealed that 36b provided potential opportunities to new antipsychotic drugs with the multiple antipsychotic-like properties.