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To develop a new therapeutic agent for sleep disorders, we synthesized a novel series of tricyclic indan derivatives and evaluated them for their binding affinity to melatonin receptors. In our previous paper, we proposed a conformation of the methoxy group favorable for the binding of the MT1 receptor. To fix the methoxy group in an active conformation, we decided to synthesize conformationally restricted tricyclic indan analogues with the oxygen atom in the 6-position incorporated into a furan, 1,3-dioxane, oxazole, pyran, morpholine, or 1,4-dioxane ring system. Among these compounds, indeno[5,4-b]furan analogues were found to be the most potent and selective MT1 receptor ligands and to have superior metabolic stability. The optimization of substituents led to (S)-(−)-22b, which showed very strong affinity for human MT1 (Ki = 0.014 nM), but no significant affinity for hamster MT3 (Ki = 2600 nM) or other neurotransmitter receptors. The pharmacological effects of (S)-(−)-22b were studied in experimental animals, and it was found that a dose of 0.1 mg/kg, po promoted a sleep in freely moving cats, as demonstrated by a decrease in wakefulness and increases in slow wave sleep and rapid eye movement sleep, which lasted for 6 h after administration. Melatonin (1 mg/kg, po) also had a sleep-promoting effect, though it lasted only 2 h. A new chiral method for the synthesis of (S)-(−)-22b starting from 60, which was prepared from 59 employing asymmetric hydrogenation with the (S)-2,2‘-bis(diphenylphosphino)-1,1‘-binaphthyl−Ru complex, was developed. (S)-(−)-22b (TAK-375) is currently under clinical trial for the treatment of insomnia and circadian rhythm disorders.

We synthesized a novel series of benzocycloalkene derivatives and evaluated their binding affinities to melatonin receptors. To control the spatial position of the amide group, one of the important pharmacophores, we incorporated an endo double bond, an exo double bond (E- and Z-configurations), and a chiral center (R- and S-configurations) at position 1. The indan derivatives with the S-configuration at position 1 were the most promising in terms of potency and selectivity for the human melatonin receptor (MT1 site), while compounds with the R-configuration showed little potential. Our next attempt was to investigate the most favorable conformation of the methoxy group, the other important pharmacophore for binding to the MT1 receptor. The introduction of a methyl group at position 5 of the indene ring conserved affinity; however, at position 7, it caused a decrease in affinity. These results suggested that the substitution at position 7 forced the methoxy group to adopt an unfavorable orientation. The optimization of the condensed ring size and substituents led to (S)-8d [(S)-N-[2-(2,3-dihydro-6-methoxy-1H-inden-1-yl)ethyl]propionamide], which had high affinity for the human MT1 receptor (Ki = 0.041 nM) but no significant affinity for the hamster MT3 receptor (Ki = 3570 nM). In addition, a practical synthetic method of chiral N-[2-(2,3-dihydro-1H-inden-1-yl)ethyl]alkanamides employing asymmetric hydrogenation with (S)-2,2‘-bis(diphenylphosphino)-1,1‘-binaphthyl−Ru has been established.

A series of 2,3-dihydro-5-benzofuranamines (5-aminocoumarans) were developed for the treatment of traumatic and ischemic central nervous system (CNS) injury. Compounds within this class were extremely effective inhibitors of lipid peroxidation in vitro and antagonized excitatory behavior coupled with peroxidative injury induced by spinal intrathecal injection of FeCl2 (mouse-FeCl2-it assay) in vivo. Selected compounds were tested for antagonistic activity on methamphetamine (MAP)-induced hypermotility resulting from dopamine release in the mouse brain. Among the compounds synthesized, compound 26n (2,3-dihydro-2,4,6,7-tetramethyl-2-[(4-phenyl-1-piperidinyl)methyl]-5-benzofuranamine) exhibited potent effects in these assays (inhibition of lipid peroxidation, IC50 = 0.07 μM; mouse-FeCl2-it assay, ID50 = 10.4 mg/kg, po; MAP-induced hypermotility, 98% inhibition, 10 mg/kg, ip). The S-(+)-form of compound 26n dihydrochloride (TAK-218), which has 30 times more potent antagonistic activity on MAP-induced hypermotility than the R-(−)-form, improved more significantly the survival rate in the cerebral ischemia model (rat, 1−3 mg/kg, ip) during the period of 1−14 days after ischemia and decreased functional disorders in the traumatic brain injury model (rat, 0.1−1 mg/kg, ip) 3−14 days after injury. These results imply a role for dopamine in deterioration of CNS function after ischemic and traumatic injury. TAK-218 is a promising compound for the treatment of stroke and CNS trauma and is now under clinical investigation.

Abstract: Objective: To examine the effects of three nitric oxide synthase inhibitors on survival in a murine sepsis model.Design: Prospective randomized experimental trials.Setting: Laboratory.Subjects: Female Balb/c mice.Interventions:Escherichia coli (108 colony-formingunits/body) were injected into the peritoneal cavities of Balb/c mice. NG-nitro-L-arginine-methyl-ester, NG-monomethyl-L-arginine, or N-iminoethyl-L-ornithine was given at various concentrations, intraperitoneally, one hour before bacterial challenge.Measurements: One hundred and fifteen animals were observed for survival.Results: These inhibitors provided the mice no protection from the bacterial challenge. Notably, pretreatment with NG-nitro-L-arginine-methyl-ester (100 mg/kg i.p.) actually reduced survival time afterE. coli challenge.Conclusions: Inhibition of nitric oxide production improved neither the survival time nor rate in this murine sepsis model.