P. Krogsgaard-Larsen

Glutamate and gaba receptors and transporters : structure,function and pharmacology

1. Ionotropic Glutamate Receptors: Functional and Pharmacological Properties in Relation to Constituent Subunits, Stuart G. Cull-Candy 2. Molecular Structure of Ionotropic Glutamate Receptors, Jan Egebjerg and Henrik S Jensen 3. Glutamate Receptor Trafficking, Guido Meyer and Jeremy M. Henley 4. Pharmacology of NMDA Receptors, David E. Jane 5. Pharmacology of AMPA/kainate Receptors, Ulf Madsen, Tommy N. Johansen, Tine B. Stensbol and Povl Krogsgaard-Larsen 6. Metabotropic Glutamate Receptors (mGluRs): Structure and Functions, J-P. Pin, L. Fagni and J. Bockaert 7. Pharmacology of Metabotropic Receptors, Darryle D. Schoepp and James A. Monn 8. Insights into GABAA Receptor Complexity From the Study of Cerebellar Granule Cells: Synaptic and Extrasynaptic Receptors, William Wisden and Mark Farrant 9. GABAA Receptor Complex: Structure and Function, Richard W. Olsen and Robert L. Macdonald 10. GABAA Receptor Complex: Structural Requirements for Ligand Interactions, P. Krogsgaard-Larsen, B. Ebert, U. Kristiansen, B. Madsen 11. Molecular Structure of the GABAB Receptors, N. Klix and B. Bettler 12. Phamacology of GABAB Receptors, N. G. Bowery 13. Structure, Function and Regulation of Glutamate Transporters, Line M. Levy 14. GABA Transporters: Functional and Pharmacological Properties, Arne Schousboe and Baruch Kanner 15. Transgenic Models for Glutamate Receptor Function, A.J. Doherty and G.L. Collingridge 16. Transgenic Models for GABAA Receptor Function, H. Mohler 17. Glutamatergic transmission: Therapeutic Prospects for Schizophrenia and Alzheimers Disease, Nuri B. Farber, John W. Newcomer and John W. Olney 18. GABA-ergic Transmission: Therapeutic Prospects, Christian Thomsen and Bjarke Ebert MRC Centre, UK, R. Dingledine, Emory University of Medicine, USA, D.E. Jane, Univeristy of Bristol, UK, U. Madsen, Danish School of Pharmacy, S. Nakanishi, Kyoto University Faculty of Medicine, Japan, P.L. Ornstien and D.D. Schoepp, Lilly Corporate Centre, USA, M. Neilsen, St Hans Hospital, Denmark, R.L. Macdonald, University of Michegan Medical Centre, USA and R. Olsen, University of California, USA, P. Krogsgaard-Larsen, Danish School of Pharmacy, B. Bettler, Novartis Pharma Inc., Switzerland, W. Froestl, Novartis Pharma Inc., Switzerland, G. Gegelashvili, Danish School of Pharmacy, N.C. Damnbolt, University of Oslo, Norway, A. Shousboe, Danish School of Pharmacy, B.I. Kanner, The Hebrew University, Israel, G.L. Collingridge, Bristol University, UK, E. Mohler, Institute of Pharmacology, Switzerland, J. Drejer, NeuroSearch, Denmark, A.G. Chapman, Institute of Psychiatry, UK.

Excitatory amino-acid receptor agonists. Synthesis and pharmacology of analogues of 2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid

Summary We have previously proposed the existence of a lipophilic cavity of the 2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA) receptor recognition site capable of accommodating alkyl substituents of limited size in the 5-position of the isoxazole ring. In order to indirectly elucidate the approximate extent of this proposed cavity we have synthesized and pharmacologically characterized a number of AMPA analogues. For most of these AMPA analogues, a positive correlation between AMPA receptor affinity and agonist effect was observed. The only exception was demethyl-AMPA ( 8a ), which showed relatively high AMPA receptor affinity (IC 50 = 0.27 μM) but remarkably weak agonist potency (EC 50 = 900 μM). Whereas the ethyl analogue of AMPA (Et-AMPA) (IC 50 = 0.030 μM; EC 50 = 2.3 μM) has previously been shown to be slightly more potent than AMPA (IC 50 = 0.040 μM; EC 50 = 3.5 μM), substitutions of a propyl or a butyl group for the methyl group of AMPA to give 8b (IC 50 = 0.090 μM; EC 50 = 5.0 μM) or 8f (IC 50 = 1.0 μM; EC 50 = 32 μM), respectively, result in progressive loss of the AMPA agonist effect. Analogues containing larger groups, such as isopentyl ( 8e ), 1-propylbutyl ( 8g ), 2,2-dimethylpropyl ( 8h ), or benzyl ( 14 ) groups, were very weak or totally inactive as AMPA receptor ligands.

Inhibitors of AMPA and kainate receptors

The glutamate receptor system is implicated in the development and maintenance of epileptic seizures, and animal studies have disclosed potent anticonvulsant activity of a number of inhibitors of AMPA and/or kainate (KA) receptor activity. These results make such inhibitors potential future antiepileptic drugs. Different series of compounds with inhibitory activity towards AMPA receptors have been developed. Most of these inhibitors are structurally derived from AMPA, quinoxalinedione or 2,3-benzodiazepine. In contrast, only a limited number of inhibitors of KA receptor activity have been developed, most of which contain quinoxalinedione or decahydroisoquinoline skeletons. In spite of promising anticonvulsant activity in various animal model studies, no AMPA/KA receptor inhibitors are in clinical use against epilepsy today. Based on molecular biology studies, AMPA and KA receptors are at present divided into four and five subtypes, respectively, and attempts to develop subtype selective compounds have been initiated. Future studies and development of such compounds will indicate whether AMPA/KA receptor inhibition is a feasible therapeutic strategy for the treatment of epilepsy.

Synthesis and pharmacology of (RS)-2-amino-3-(3-hydroxy-5-trifluoromethyl-4-isoxazolyl)propionic acid, a potent AMPA receptor agonist

Abstract Three isoxazole bioisosteres of glutamic acid derived from the specific AMPA receptor agonist ( RS )-2-amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionic acid (AMPA) were synthesized and tested electrophysiologically and in different receptor binding systems. ( RS )-2-Amino-3-(3-hydroxy-5-trifluoromethyl-4-isoxazolyl)propionic acid (trifluoro-AMPA, 8) showed more potent agonist activity (EC 50 2.3 μM) and lower affinity (IC 50 0.08 μM) for AMPA receptors than AMPA itself (EC 50 3.5 μM and IC 50 0.04 μM, respectively). Like AMPA, trifluoro-AMPA ( 8 ) did not bind significantly to N -methyl- d -aspartic acid (NMDA) receptor sites, but trifluoro-AMPA ( 8 ) was more potent as an inhibitor of [ 3 H]kainic acid ([ 3 H]KAIN) binding (IC 50 7.1 μM) than AMPA (IC 50 32 μM). ( RS )-2-Amino-3-(3-chloro-5-methyl-4-isoxazolyl)propionic acid ( 14 ), the 3-chloro analogue of AMPA, and the isomeric compound ( RS )-2-amino-3-(3-chloro-4-methyl-5-isoxazolyl)propionic acid ( 15 ), did not show significant neuroexcitatory effects at or affinities for AMPA, NMDA, or KAIN receptor sites.

Pharmacology and toxicology of ATOA, an AMPA receptor antagonist and a partial agonist at GluR5 receptors

(RS)-2-Amino-3-[3-(carboxymethoxy)-5-tert-butyl-4-isoxazolyl]propi onic acid (ATOA) has previously been described as an antagonist at (RS)-2-amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionic acid (AMPA) receptors with an IC50 value of 150 microM towards AMPA-induced depolarisation in the rat cortical wedge preparation. ATOA has now been shown also to be a partial agonist at recombinant GluR5 receptors, expressed in Xenopus oocytes, with an EC50 value of 170 microM and a relative efficacy of 0.17 +/- 0.04 compared with responses produced by kainic acid (1.0). Using cultured cerebral cortical neurones as a test system and leakage of lactate dehydrogenase (LDH) as an indicator of cell damage, ATOA was shown to be cytotoxic (ED50 > 300 microM), though much less toxic than the structurally related dual AMPA and GluR5 agonist, (RS)-2-amino-3-(3-hydroxy-5-tert-butyl-4-isoxazolyl)propionic acid (ATPA) (ED50 = 14 +/- 2 microM). The toxic effect of ATPA was sensitive to 6,7-dinitroquinoxaline-2,3-dione (DNQX) but was not significantly reduced by the selective AMPA receptor antagonist, (RS)-2-amino-3-[3-(carboxymethoxy)-5-methyl-4-isoxazolyl]propionic acid (AMOA). The toxicity of ATOA (1 mM) could not be significantly attenuated by co-administration of AMOA (300 microM) or DNQX (25 microM). A structure-activity analysis indicates that the tert-butyl group of ATPA and ATOA facilitates the interaction of these compounds with GluR5 receptors.

Excitatory amino acid receptor ligands: asymmetric synthesis, absolute stereochemistry and pharmacology of (R)- and (S)-homoibotenic acid.

The (R)- and (S)-forms of 2-amino-3-(3-hydroxyisoxazol-5-yl)propionic acid (homoibotenic acid, HIBO) were synthesized, using (S)-BOC-phenylalanine as a chiral auxiliary and their absolute stereochemistry correlated with that of (R)-Br-HIBO. The enantiomeric excesses for (R)-HIBO (1) (> 99.5%) and (S)-HIBO (2) (99.5%) were determined using chiral HPLC. Whereas compounds 1 and 2 were equipotent inhibitors of the binding of [3H]glutamic acid in the presence of calcium chloride, 2 showed AMPA agonist activity and 1 very weak NMDA agonist activity.

Ibotenic acid analogues. Synthesis and biological testing of two bicyclic 3-isoxazolol amino acids

The bicyclic 3-isoxazolol amino acids (RS)-3-hydroxy-4,5,6,7-tetrahydroisoxazolo[4,5-c]pyridine-4-carboxylic acid (5, 4-HPCA) and (RS)-3-hydroxy-4,5,6,7-tetrahydroisoxazolo[4,5-c]pyridine-6-carboxylic acid (11, 6-HPCA) were synthesized as model compounds for studies of the structural requirements of central excitatory amino acid neurotransmitter receptors. 4-HPCA was synthesized via introduction of a methoxycarbonyl group into the 4-position of the lithiated N-nitroso intermediate 1. The key reaction in the synthesis of 6-HPCA is an intramolecular N-alkylation of the appropriately substituted acetamidomalonate derivative 7 using sodium hydride as a base. On the basis of the pKA values for 4-HPCA the existence of an intramolecular hydrogen bond in the zwitterionic form of this amino acid is proposed. 6-HPCA was shown by 1H NMR spectroscopy to adopt preferentially a conformation with the carboxylate group in an equatorial position. 4- and 6-HPCA were tested as agonists and antagonists at excitatory amino acid receptors on neurones in the cat spinal cord using microelectrophoretic techniques. Neither compound showed significant effects at these receptors.

Excitatory amino acid receptors: Multiplicity and ligand specificity of the NMDA and AMPA receptor subtypes

Abstract Central excitatory amino acid (EAA) receptors are most conveniently subdivided into five main classes, most of which, if not all, are heterogeneous: NMDA, AMPA, kainic acid (KAIN), metabotropic, and L-AP4 receptors. The AMPA and KAIN receptors have very similar pharmacology in vivo, and these receptors are often collectively named non-NMDA EAA receptors. The Amanita muscaria constituent, ibotenic acid, which is an analogue of glutamic acid, interacts more or less effectively with all subtypes of EAA receptors. Ibotenic acid has, however, been used as a lead structure for the development of a number of specific ligands for NMDA and AMPA receptors. Thus, the aspartic acid analogue of ibotenic acid, AMAA, is a specific NMDA agonist. Whereas AMPA and 4-AHCP are specific agonists at AMPA receptors, APPA is a partial AMPA agonist, and AMOA is an antagonist at non-NMDA EAA receptors.