ABSTRACT
(3-tert-Butyl-7-(5-methylisoxazol-3-yl)-2-(1-methyl-1H-1,2,4-triazol-5-ylmethoxy)pyrazolo[1,5-d][1,2,4]triazine (1) was recently identified as a functionally selective, inverse agonist at the benzodiazepine site of GABA(A) alpha5 receptors and enhances performance in animal models of cognition. The routes of metabolism of this compound in vivo in rat have been well characterised, the identities of the major metabolites are confirmed by synthesis and their biological profiles were evaluated. An unusual oxidation of the pyrazolo[1,5-d][1,2,4]triazine core to the corresponding pyrazolo[1,5-d][1,2,4]triazin-4(5H)-one scaffold by aldehyde oxidase has been observed.
Subject(s)
GABA Agonists/metabolism , GABA Agonists/pharmacokinetics , GABA-A Receptor Agonists , Isoxazoles/metabolism , Isoxazoles/pharmacokinetics , Protein Subunits/agonists , Triazines/metabolism , Triazines/pharmacokinetics , Animals , Dogs , Dose-Response Relationship, Drug , GABA Agonists/chemical synthesis , Hydrolysis , Isoxazoles/chemical synthesis , Macaca mulatta , Mice , Molecular Conformation , Rats , Stereoisomerism , Structure-Activity Relationship , Tissue Distribution , Triazines/chemical synthesisABSTRACT
(3-tert-Butyl-7-(5-methylisoxazol-3-yl)-2-(1-methyl-1H-1,2,4-triazol-5-ylmethoxy)pyrazolo[1,5-d][1,2,4]triazine (13) has been identified as a functionally selective, inverse agonist at the benzodiazepine site of GABA(A) alpha5 receptors. 13 is orally bioavailable, readily penetrates the CNS, and enhances performance in animal models of cognition. It does not exhibit the convulsant, proconvulsant, or anxiogenic activity associated with nonselective GABA(A) inverse agonists.
Subject(s)
Cognition/drug effects , GABA-A Receptor Agonists , Isoxazoles/chemical synthesis , Nootropic Agents/chemical synthesis , Triazines/chemical synthesis , Administration, Oral , Animals , Binding Sites , Biological Availability , Dogs , Isoxazoles/adverse effects , Isoxazoles/pharmacology , Maze Learning/drug effects , Mice , Nootropic Agents/adverse effects , Nootropic Agents/pharmacology , Patch-Clamp Techniques , Protein Subunits , Radioligand Assay , Rats , Receptors, GABA-A/metabolism , Triazines/adverse effects , Triazines/pharmacologyABSTRACT
In pursuit of a GABA(A) alpha5-subtype-selective inverse agonist to enhance cognition, a series of 6,7-dihydro-2-benzothiophen-4(5H)-ones has been identified as a novel class of GABA(A) receptor ligands. These thiophenes have higher binding affinity for the GABA(A) alpha5 receptor subtype compared to the GABA(A) alpha1, alpha2, and alpha3 subtypes, and several analogues exhibit high GABA(A) alpha5 receptor inverse agonism. 6,6-Dimethyl-3-(2-hydroxyethyl)thio-1-(thiazol-2-yl)-6,7-dihydro-2-benzothiophen-4(5H)-one (43) has been identified as a full inverse agonist at the GABA(A) alpha5 receptor and is functionally selective over the other major GABA(A) receptor subtypes. 43 readily penetrates into the CNS to give selective occupancy of GABA(A) alpha5 receptors. In addition, 43 enhances cognitive performance in rats in the delayed 'matching-to-place' Morris water maze test-a hippocampal-dependent memory task-without the convulsant or proconvulsant activity associated with nonselective, GABA(A) receptor inverse agonists.
Subject(s)
Cognition/drug effects , GABA Agonists/chemical synthesis , Nootropic Agents/chemical synthesis , Receptors, GABA-A/drug effects , Thiazoles/chemical synthesis , Thiophenes/chemical synthesis , Animals , Brain/metabolism , Cell Line , Female , GABA Agonists/adverse effects , GABA Agonists/pharmacology , Hippocampus/physiology , Humans , In Vitro Techniques , Ligands , Male , Maze Learning/drug effects , Memory/drug effects , Mice , Nootropic Agents/adverse effects , Nootropic Agents/pharmacology , Oocytes/drug effects , Oocytes/physiology , Patch-Clamp Techniques , Protein Subunits , Radioligand Assay , Rats , Seizures/chemically induced , Structure-Activity Relationship , Thiazoles/adverse effects , Thiazoles/pharmacology , Thiophenes/adverse effects , Thiophenes/pharmacology , Xenopus laevisABSTRACT
Nonselective inverse agonists at the benzodiazepine binding site on the GABA-A chloride ion channel enhance cognitive performance in animals but cannot be used in the treatment of cognitive disorders because of anxiogenic and convulsant side effects. We have identified a novel series of GABA-A alpha5 receptor ligands during our search for alpha5 receptor inverse agonists as potential cognition enhancers. In particular, 6,6-dimethyl-3-(2-hydroxyethyl)thio-1-(thiazol-2-yl)-6,7-dihydro-2-benzothiophen-4(5H)-one (26) has been identified as a functionally selective GABA-A alpha5 inverse agonist.
