title: Novel class of amino acid antagonists at non-N-methyl-D-aspartic acid excitatory amino acid receptors. Synthesis, in vitro and in vivo pharmacology, and neuroprotection.
abstract: The isoxazole amino acid 2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl) propionic acid (AMPA) (1), which is a highly selective agonist at the AMPA subtype of excitatory amino acid (EAA) receptors, has been used as a lead for the development of two novel EAA receptor antagonists. One of the compounds, 2-amino-3-[3-(carboxymethoxy)-5-methylisoxazol-4-yl]propionic acid (AMOA, 7), was synthesized via O-alkylation by ethyl chloroacetate of the amino acid protected AMPA derivative 4. The other compound, 2-amino-3-[2-(3-hydroxy-5-methylisoxazol-4-yl)-methyl-5-methyl-3-+ ++oxoisoxazolin -4-yl]propionic acid (AMNH, 14) was synthesized with use of 4-(chloromethyl)-3-methoxy-5-methylisoxazole (8) as the starting material. The intermediate 4-(chloromethyl)-2-(3-methoxy-5-methylisoxazol-4-yl)methyl-5-me thylisoxazolin- 3-one (11) was converted into the acetamidomalonate (12), which was stepwise deprotected to give 14. Compounds 7 and 14 were stable in aqueous solution at pH values close to physiological pH. Neither 7 nor 14 showed detectable affinities for the receptor, ion channel, or modulatory sites of the N-methyl-D-aspartic acid (NMDA) receptor complex. Quantitative receptor autoradiographic and conventional binding techniques were used to study the affinities of 7 and 14 for non-NMDA receptor sites. Both compounds were inhibitors of the binding of [3H]AMPA (IC50 = 90 and 29 microM, respectively). Compounds 14 and 7 were both very weak inhibitors of the high-affinity binding of radioactive kainic acid [( 3H]KAIN). Compound 14, but not 7, was, however, shown to be an inhibitor of low-affinity [3H]KAIN binding (IC50 = 40 microM) as determined in the presence of 100 mM calcium chloride. In the rat cortical slice preparation, 7 was shown to antagonize excitation induced by 1 with some selectivity, whereas 14 proved to be a rather selective antagonist of KAIN-induced excitation. Both antagonists showed very weak effects on the excitatory effects of NMDA. Compound 7 was a poor antagonist of excitation by quisqualic acid (2), whereas 14 did not affect excitation by this nonselective AMPA receptor agonist. On cat spinal neurones, both 7 and 14 reduced excitations by 1 and KAIN, but, again, the excitatory effects of 2 were much less sensitive. Compound 14 and, in particular, 7 effectively protected rat striatal neurones against the neurotoxic effects of KAIN, whereas the toxic effects of 1 were reduced only by 7. Neither antagonist showed protection against the cell damage caused by intrastriatal injection of the NMDA agonist quinolinic acid.(ABSTRACT TRUNCATED AT 400 WORDS)
authors.affiliation: Department of Organic Chemistry, Royal Danish School of Pharmacy, Copenhagen, Denmark.
authors.forename: P
authors.initials: P
authors.lastname: Krogsgaard-Larsen
authors.forename: J W
authors.initials: JW
authors.lastname: Ferkany
authors.forename: E O
authors.initials: EO
authors.lastname: Nielsen
authors.forename: U
authors.initials: U
authors.lastname: Madsen
authors.forename: B
authors.initials: B
authors.lastname: Ebert
authors.forename: J S
authors.initials: JS
authors.lastname: Johansen
authors.forename: N H
authors.initials: NH
authors.lastname: Diemer
authors.forename: T
authors.initials: T
authors.lastname: Bruhn
authors.forename: D T
authors.initials: DT
authors.lastname: Beattie
authors.forename: D R
authors.initials: DR
authors.lastname: Curtis
mesh_terms: D000818:Animals; D001345:Autoradiography; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D002540:Cerebral Cortex / Q000187:drug effects / Q000502:physiology*; D016291:Dizocilpine Maleate / Q000378:metabolism; D005998:Glycine / Q000378:metabolism; D007051:Ibotenic Acid / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D066298:In Vitro Techniques; D007202:Indicators and Reagents; D007555:Isoxazoles / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D008297:Male; D015394:Molecular Structure; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D011422:Propionates / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects* / Q000378:metabolism; D013329:Structure-Activity Relationship; D014316:Tritium; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid
chemical_list: D007202:Indicators and Reagents; D007555:Isoxazoles; D011422:Propionates; D016194:Receptors, N-Methyl-D-Aspartate; D014316:Tritium; C066116:2-amino-3-(3-(carboxymethoxy)-5-methylisoxazol-4-yl)propionic acid; C066117:2-amino-3-(2-(3-hydroxy-5-methylisoxazol-4-yl)methyl-5-methyl-3-oxoisoxazolin-4-yl)propionic acid; D007051:Ibotenic Acid; D016291:Dizocilpine Maleate; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; D005998:Glycine