Synthesis and Enantiopharmacology of New AMPA-Kainate Receptor Agonists

Abstract

Regioisomeric 3-carboxyisoxazolinyl prolines [CIP-A (+/-)-6 and CIP-B (+/-)-7] and 3-hydroxyisoxazolinyl prolines [(+/-)-8 and (+/-)-9] were synthesized and assayed for glutamate receptor activity. The tests were carried out in vitro by means of receptor binding techniques, second messenger assays, and the rat cortical wedge preparation. CIP-A showed a good affinity for both 2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA) and kainic acid (KAIN) receptors. These results were confirmed in the cortical slice model where CIP-A displayed an EC(50) value very close to that of AMPA. The convulsant properties of all the compounds were evaluated in vivo on DBA/2 mice after icv injection. CIP-A showed a convulsant activity, measured as tonus and clonus seizures, 18-65 times higher than that produced by AMPA. It was also quite active after ip administration, since it induced seizures in mice at doses as low as 3.2 nmol/mouse. On the basis of the above-reported results we prepared and tested the enantiomers of CIP-A and CIP-B, obtained by reacting (S)-3,4-didehydroproline and (R)-3,4-didehydroproline, respectively, with ethoxycarbonylformonitrile oxide. In all the tests the S-form, CIP-AS [(-)-6], emerged as the eutomer evidencing common stereochemical requirements with the reference compounds AMPA and KAIN. Through modeling studies, carried out on CIP-A, AMPA, and KAIN, active conformations for CIP-AS and AMPA at AMPA receptors as well as for CIP-AS and KAIN at KAIN receptors are suggested.

Neuroprotective Effects of the Novel Glutamate Transporter Inhibitor (–)-3-Hydroxy-4,5,6,6a-tetrahydro-3aH-pyrrolo[3,4-d]-isoxazole-4-carboxylic Acid, Which Preferentially Inhibits Reverse Transport (Glutamate Release) Compared with Glutamate Reuptake

“…This neuroprotective effect cannot be ascribed to a direct antagonism at Glu receptors (Conti et al, 1999b), nor can it be due to inhibition of GABA reuptake (C. Thomsen, personal communication). Thus, we propose that it is the consequence of lower levels of extracellular Glu due to the inhibition of EAAT-mediated Glu release.…”

Efficient synthesis of kainic acid analogues

“…According to a literature report, 9 the synthesis of CIP-A and CIP-B, as pure enantiomers, has been accomplished as depicted in Scheme 1. The major drawbacks associated to the described procedure 9 are: i) the low reactivity of dipolarophile 1 and ii) the failure to separate cycloadduct 3 from 4 by column chromatography.…”

“…In red is highlighted the structural part representing the skeleton of glutamic acid, homoglutamic acid (CIP-B) or aspartic acid (HIP-A). [8][9][10][11] Figure 1. Structure of (S)-AMPA, KA and their molecular hybrids.…”

“…8,9 The eutomer of CIP-A was characterized by the S configuration at the amino acidic stereogenic center. On the contrary, both HIP-A and HIP-B turned out to be inactive at metabotropic and ionotropic glutamate receptors whereas they were provided with an interesting inhibitory activity at glutamate transporters.…”

Synthesis of Novel Pyrrolo[3,4‐d]pyrazole‐dicarboxylic Acids and Evaluation of Their Interaction with Glutamate Receptors

“…On this background, we have previously designed and prepared (S)-CIP-A (Fig. 1), a bicyclic 4,5-dihydroisoxazole carboxylic acid embedding a folded conformation of Glu, which turned out to be a quite potent agonist at both AMPA and KA receptors [8]. If the selection of an appropriate conformation can account for the discrimination between iGluRs and mGluRs, the selectivity among the different classes of the same receptor family can be often attained through the insertion of a specific functionality or group in the amino acid skeleton, capable of establishing an additional interaction or a steric repulsion with the binding site of a given glutamate receptor subtype.…”