Novel Analogues of (R)-5-(Methylamino)-5,6-dihydro-4H-imidazo[4,5,1-ij]quinolin-2(1H)-one (Sumanirole) Provide Clues to Dopamine D2/D3 Receptor Agonist Selectivity

J Med Chem. 2016 Apr 14;59(7):2973-88. doi: 10.1021/acs.jmedchem.5b01612. Epub 2016 Apr 1.


Novel 1-, 5-, and 8-substituted analogues of sumanirole (1), a dopamine D2/D3 receptor (D2R/D3R) agonist, were synthesized. Binding affinities at both D2R and D3R were higher when determined in competition with the agonist radioligand [(3)H]7-hydroxy-N,N-dipropyl-2-aminotetralin (7-OH-DPAT) than with the antagonist radioligand [(3)H]N-methylspiperone. Although 1 was confirmed as a D2R-preferential agonist, its selectivity in binding and functional studies was lower than previously reported. All analogues were determined to be D2R/D3R agonists in both GoBRET and mitogenesis functional assays. Loss of efficacy was detected for the N-1-substituted analogues at D3R. In contrast, the N-5-alkyl-substituted analogues, and notably the n-butyl-arylamides (22b and 22c), all showed improved affinity at D2R over 1 with neither a loss of efficacy nor an increase in selectivity. Computational modeling provided a structural basis for the D2R selectivity of 1, illustrating how subtle differences in the highly homologous orthosteric binding site (OBS) differentially affect D2R/D3R affinity and functional efficacy.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Benzimidazoles / chemistry*
  • Binding Sites
  • CHO Cells
  • Chemistry Techniques, Synthetic
  • Cricetulus
  • Humans
  • Ligands
  • Models, Molecular
  • Molecular Dynamics Simulation
  • Radioligand Assay
  • Receptors, Dopamine D2 / agonists*
  • Receptors, Dopamine D2 / genetics
  • Receptors, Dopamine D3 / agonists*
  • Receptors, Dopamine D3 / genetics
  • Structure-Activity Relationship*


  • Benzimidazoles
  • DRD2 protein, human
  • Ligands
  • Receptors, Dopamine D2
  • Receptors, Dopamine D3
  • U 95666E