3,4-Dihydro-2(1H)-quinolinone as a Novel Antidepressant Drug:  Synthesis and Pharmacology of 1-[3-[4-(3-Chlorophenyl)-1-piperazinyl]propyl]-3,4- dihydro-5-methoxy-2(1H)-quinolinone and Its Derivatives

To develop a novel antidepressant drug with central nervous system-stimulating activity, we prepared a series of 1-[ω-(4-substituted phenyl-1-piperazinyl)alkyl]-3,4-dihydro-2(1H)-quinolinone derivatives and examined their activities by their effects at 30 and 100 mg/kg po on the sleeping time of mice anesthetized with halothane and on the time required for recovery from coma induced in mice by cerebral concussion. We examined their binding affinities for σ receptors by evaluating their ability to inhibit [³H]-1,3-di(o-tolyl)guanidine ([³H]DTG) binding to the rat whole brain membrane in comparison with three putative σ receptor agonists:  1,3-di(o-tolyl)guanidine (DTG, 66), (+)-1,2,3,4,5,6-hexahydro-6,11-dimethyl-3-(2-propenyl)-2,6-methano-3-benzazecin-8-ol (SKF10,047, 67), and (+)-1,2,3,4,5,6-hexahydro-6,11-dimethyl-3-(3-methyl-2-butenyl)-2,6-methano-3-benzazecin-8-ol (pentazocine, 68). Among the series of derivatives, 1-[3-[4-(3-chlorophenyl)-1-piperazinyl]propyl]-3,4-dihydro-5-methoxy-2(1H)-quinolinone hydrochloride (34b) and its mesylate (34c), at a dose of 30 mg/kg po, reduced the sleeping time and the time for recovery from coma and they inhibited [³H]DTG binding for σ receptors. The putative σ receptor agonists reduced the sleeping time and the time for recovery from coma whereas two σ receptor antagonists, α-(4-fluorophenyl)-4-(5-fluoro-2-pyrimidinyl)-1-piperazinebutanol hydrochloride (BMY14802, 69) and cis-9-[3-(3,5-dimethyl-1-piperazinyl)propyl]carbazole dihydrochloride (rimcazole, 70), were inactive in the two tests. Preadministration of the putative σ receptor antagonists 69 (3 mg/kg po) and 70 (30 mg/kg po) completely antagonized the actions of 34b and the σ receptor agonists in the test for recovery from coma. These results suggested that 34b and 34c are σ receptor agonists. Furthermore, a single administration of 1 and 10 mg/kg po 34b and 34c showed antidepressant-like activity by reducing the immobility time in the forced-swimming test with mice, while a tricyclic antidepressant, 10,11-dihydro-N,N-dimethyl-5H-dibenz[b,f]azepine-5-propanamine hydrochloride (imipramine, 1) (10 and 30 mg/kg po), did not reduce the time after a single administration. 1 reduced the time after repeated administration of 30 mg/kg po once a day for 4 days. The structure−activity relationship of the series of compounds is also discussed.