RESUMO
Halogenated analogues of the neurotoxic alkaloid muscimol were prepared with fluorine, iodine or trifluoromethyl at the 4 position of the isoxazole ring system. These compounds were investigated as agonists for GABAA receptors. Only the C-4 fluorine-containing analogue proved to be an active compound in these assays. The fluoro analogue was less active than muscimol, however it showed differential activity between synaptic (α1 ß2 γ2 ) and extrasynaptic (α4 ß2 γ) GABAA receptors, having a similar potency to the neurotransmitter GABA for the extrasynaptic (α4 ß2 γ) receptor.
Assuntos
Flúor/química , Agonistas GABAérgicos/química , Muscimol/química , Animais , Cristalografia por Raios X , Agonistas GABAérgicos/síntese química , Agonistas GABAérgicos/metabolismo , Conformação Molecular , Muscimol/síntese química , Muscimol/metabolismo , Oócitos/metabolismo , Receptores de GABA-A/genética , Receptores de GABA-A/metabolismo , Xenopus laevis/crescimento & desenvolvimento , Xenopus laevis/metabolismoRESUMO
Ten analogs of muscimol and thiomuscimol in which the amino function was delocalized in an amidinic system were prepared by N2 alkylation of 6-aryl-3-aminopyridazines with (chloromethyl)isoxazole or (chloromethyl)isothiazole derivatives. These muscimol and thiomuscimol derivatives show potent binding properties for GABA-A receptors (they displace [3H]GABA and [3H]gabazine) and provoke convulsions after iv injections. They fit well with the model pharmacophore proposed by our group for the GABA-A antagonists and show similar structure-activity profiles to that of the pyridazinyl-GABAs.
Assuntos
Antagonistas de Receptores de GABA-A , Muscimol/análogos & derivados , Piridazinas/síntese química , Animais , Ligação Competitiva , Convulsivantes/síntese química , Feminino , Técnicas In Vitro , Camundongos , Modelos Moleculares , Conformação Molecular , Muscimol/síntese química , Muscimol/metabolismo , Muscimol/farmacologia , Piridazinas/metabolismo , Piridazinas/farmacologia , Ensaio Radioligante , Ratos , Receptores de GABA-A/metabolismo , Relação Estrutura-AtividadeRESUMO
A series of bioisosteric 4-(aminomethyl)-1-hydroxypyrazole (4-AHP) analogues of muscimol, a GABA(A) receptor agonist, has been synthesized and pharmacologically characterized at native and selected recombinant GABA(A) receptors. The unsubstituted 4-AHP analogue (2a) (EC(50) 19 µM, R(max) 69%) was a moderately potent agonist at human α(1)ß(2)γ(2) GABA(A) receptors, and in SAR studies substitutions in the 3- and/or 5-position were found to be detrimental to binding affinities. Ligand-receptor docking in an α(1)ß(2)γ(2) GABA(A) receptor homology model along with the obtained SAR indicate that 2a and muscimol share a common binding mode, which deviates from the binding mode of the structurally related antagonist series based on 4-(piperidin-4-yl)-1-hydroxypyrazole (4-PHP, 1). Selectivity for α(1)ß(2)γ(2) over ρ(1) GABA(A) receptors was observed for the 5-chloro, 5-bromo, and 5-methyl substituted analogues of 2a illustrating that even small differences in structure can give rise to subtype selectivity.
Assuntos
Agonistas de Receptores de GABA-A/farmacologia , Muscimol/análogos & derivados , Simulação por Computador , Agonistas de Receptores de GABA-A/síntese química , Espectroscopia de Ressonância Magnética , Modelos Moleculares , Muscimol/síntese química , Muscimol/farmacologia , Espectrometria de Massas por Ionização por Electrospray , Relação Estrutura-AtividadeAssuntos
Proteínas de Transporte/antagonistas & inibidores , Antagonistas GABAérgicos/síntese química , Proteínas de Membrana/antagonistas & inibidores , Proteínas de Membrana Transportadoras , Muscimol/análogos & derivados , Transportadores de Ânions Orgânicos , Prolina/análogos & derivados , Animais , Encéfalo/metabolismo , Clonagem Molecular , Desenho de Fármacos , Antagonistas GABAérgicos/farmacologia , Antagonistas GABAérgicos/uso terapêutico , Proteínas da Membrana Plasmática de Transporte de GABA , Estrutura Molecular , Muscimol/síntese química , Muscimol/farmacologia , Muscimol/uso terapêutico , Neuroglia/efeitos dos fármacos , Neuroglia/metabolismo , Neurônios/efeitos dos fármacos , Neurônios/metabolismo , Ácidos Nipecóticos/metabolismo , Ensaio Radioligante , Proteínas Recombinantes/antagonistas & inibidores , Trítio , Ácido gama-Aminobutírico/análogos & derivados , Ácido gama-Aminobutírico/metabolismoRESUMO
Drugs used to treat various disorders target GABA A receptors. To develop alpha subunit selective compounds, we synthesized 5-(4-piperidyl)-3-isoxazolol (4-PIOL) derivatives. The 3-isoxazolol moiety was substituted by 1,3,5-oxadiazol-2-one, 1,3,5-oxadiazol-2-thione, and substituted 1,2,4-triazol-3-ol heterocycles with modifications to the basic piperidine substituent as well as substituents without basic nitrogen. Compounds were screened by [(3)H]muscimol binding and in patch-clamp experiments with heterologously expressed GABA A alpha ibeta 3gamma 2 receptors (i = 1-6). The effects of 5-aminomethyl-3 H-[1,3,4]oxadiazol-2-one 5d were comparable to GABA for all alpha subunit isoforms. 5-piperidin-4-yl-3 H-[1,3,4]oxadiazol-2-one 5a and 5-piperidin-4-yl-3 H-[1,3,4]oxadiazol-2-thione 6a were weak agonists at alpha 2-, alpha 3-, and alpha 5-containing receptors. When coapplied with GABA, they were antagonistic in alpha 2-, alpha 4-, and alpha 6-containing receptors and potentiated alpha 3-containing receptors. 6a protected GABA binding site cysteine-substitution mutants alpha 1F64C and alpha 1S68C from reacting with methanethiosulfonate-ethylsulfonate. 6a specifically covalently modified the alpha 1R66C thiol, in the GABA binding site, through its oxadiazolethione sulfur. These results demonstrate the feasibility of synthesizing alpha subtype selective GABA mimetic drugs.
Assuntos
Agonistas de Receptores de GABA-A , Receptores de GABA-A/metabolismo , Ácido gama-Aminobutírico/metabolismo , Animais , Sítios de Ligação , Encéfalo/efeitos dos fármacos , Encéfalo/metabolismo , Linhagem Celular , Eletrofisiologia , Feminino , Humanos , Isoxazóis/síntese química , Isoxazóis/química , Isoxazóis/farmacologia , Modelos Moleculares , Estrutura Molecular , Muscimol/síntese química , Muscimol/química , Muscimol/farmacologia , Mutação/genética , Oócitos , Técnicas de Patch-Clamp , Piperidinas/síntese química , Piperidinas/química , Piperidinas/farmacologia , Subunidades Proteicas/agonistas , Subunidades Proteicas/genética , Subunidades Proteicas/metabolismo , Ratos , Receptores de GABA-A/química , Receptores de GABA-A/genética , Relação Estrutura-Atividade , Xenopus laevisRESUMO
3-Isoxazolols are most often synthesized from a beta-keto ester and hydroxylamine. This cyclization typically gives rise to a major byproduct, the corresponding 5-isoxazolone. We have found that N, O-diBoc-protected beta-keto hydroxamic acids can be synthesized and cyclized to 5-substituted 3-isoxazolols without formation of any byproduct. We present a novel and versatile three-step procedure in which carboxylic acid derivatives are converted into acyl Meldrum's acids which, upon aminolysis with N, O-bis(tert-butoxycarbonyl)hydroxylamine, lead to the N, O-diBoc-protected beta-keto hydroxamic acids. These hydroxamic acid analogues were then, upon treatment with hydrochloric acid, cyclized to the corresponding 5-substituted 3-isoxazolols.