title: 4,5-Substituted 3-Isoxazolols with Insecticidal Activity Act as Competitive Antagonists of Housefly GABA Receptors.
abstract: The insect GABA receptor (GABAR), which is composed of five RDL subunits, represents an important target for insecticides. A series of 4,5-disubstituted 3-isoxazolols, including muscimol analogues, were synthesized and examined for their activities against four splice variants (ac, ad, bc, and bd) of housefly GABARs expressed in Xenopus oocytes. Muscimol was a more potent agonist than GABA in all four splice variants, whereas synthesized analogues did not exhibit agonism but rather antagonism in housefly GABARs. The introduction of bicyclic aromatic groups at the 4-position of muscimol and the simultaneous replacement of the aminomethyl group with a carbamoyl group at the 5-position to afford six 4-aryl-5-carbamoyl-3-isoxazolols resulted in compounds that exhibited significantly enhanced antagonism with IC50 values in the low micromolar range in the ac variant. The inhibition of GABA-induced currents by 100 μM analogues was approximately 1.5-4-fold greater in the ac and bc variants than in the ad and bd variants. 4-(3-Biphenylyl)-5-carbamoyl-3-isoxazolol displayed competitive antagonism, with IC50 values of 30, 34, 107, and 96 μM in the ac, bc, ad, and bd variants, respectively, and exhibited moderate insecticidal activity against houseflies, with an LD50 value of 5.6 nmol/fly. These findings suggest that these 3-isoxazolol analogues are novel lead compounds for the design and development of insecticides that target the orthosteric site of housefly GABARs.
authors.affiliation: †Division of Bioscience and Biotechnology, The United Graduate School of Agricultural Sciences, Tottori University, Tottori 680-8553, Japan.
authors.forename: Genyan
authors.initials: G
authors.lastname: Liu
authors.affiliation: §Department of Life Science and Biotechnology, Faculty of Life and Environmental Science, Shimane University, Matsue, Shimane 690-8504, Japan.
authors.forename: Fumiyo
authors.initials: F
authors.lastname: Ozoe
authors.affiliation: †Division of Bioscience and Biotechnology, The United Graduate School of Agricultural Sciences, Tottori University, Tottori 680-8553, Japan.|§Department of Life Science and Biotechnology, Faculty of Life and Environmental Science, Shimane University, Matsue, Shimane 690-8504, Japan.
authors.forename: Kenjiro
authors.initials: K
authors.lastname: Furuta
authors.affiliation: †Division of Bioscience and Biotechnology, The United Graduate School of Agricultural Sciences, Tottori University, Tottori 680-8553, Japan.|§Department of Life Science and Biotechnology, Faculty of Life and Environmental Science, Shimane University, Matsue, Shimane 690-8504, Japan.
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Ozoe
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D018756:GABA Antagonists / Q000494:pharmacology*; D015870:Gene Expression; D006793:Houseflies; D007306:Insecticides / Q000494:pharmacology*; D007555:Isoxazoles; D008958:Models, Molecular; D015394:Molecular Structure; D009118:Muscimol / Q000031:analogs & derivatives* / Q000737:chemistry; D009865:Oocytes / Q000378:metabolism; D010080:Oxazoles / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D018079:Receptors, GABA / Q000187:drug effects* / Q000235:genetics; D014982:Xenopus laevis
chemical_list: D018756:GABA Antagonists; D007306:Insecticides; D007555:Isoxazoles; D010080:Oxazoles; D018079:Receptors, GABA; D009118:Muscimol
keywords: 3-isoxazolols; RDL; competitive antagonists; insect GABA receptors; insecticidal activity; two-electrode voltage clamp