Resolution, configurational assignment, and enantiopharmacology at glutamate receptors of 2-amino-3-(3-carboxy-5-methyl-4-isoxazolyl)propionic acid (ACPA) and demethyl-ACPA

We have previously described (RS)-2-amino-3-(3-carboxy-5-methyl-4-isoxazoly l)propionic acid (ACPA) as a potent agonist at the (RS)-2-amino-3-(3-hydrox y-5-methyl-4-isoxazolyl)propionic acid (AMPA) receptor subtype of (S)-gluta mic acid (Glu) receptors. We now report the chromatographic resolution of A CPA and (RS)-2-amino-3-(3-carboxy-4-isoxazolyl)propionic acid (demethyl-ACP A) using a Sumichiral OA-5000 column. The configuration of the enantiomers of both compounds have been assigned based on X-ray crystallographic analys es, supported by circular dichroism spectra and elution orders on chiral HP LC columns. Furthermore, the enantiopharmacology of ACPA and domethyl-ACPA was investigated using radioligand binding and cortical wedge electrophysio logical assay systems and cloned metabotropic Glu receptors. (S)-ACPA showe d high affinity in AMPA binding (IC50 = 0.025 muM), low affinity in kainic acid binding (IC50 = 3.6 muM), and potent AMPA receptor agonist activity on cortical neurons (EC50 = 0.25 muM), whereas (R)-ACPA was essentially inact ive. Like (S)-ACPA, (S)-demethyl-ACPA displayed high AMPA receptor affinity (IC50 = 0.039 muM), but was found to be a relatively weak AMPA receptor ag onist (EC50 = 12 muM). The stereoselectivity observed for demethyl-ACPA was high when based on AMPA receptor affinity (eudismic ratio = 250), but low when based on electrophysiological activity (eudismic ratio = 10). (R)-Deme thyl-ACPA also possessed a weak NMDA receptor antagonist activity (IC50 = 2 20 muM), Among the enantiomers tested, only (S)-demethyl-ACPA showed activi ty at metabotropic receptors, being a weak antagonist at the mGlu(2) recept or subtype (K-B = 148 muM). Chirality 13:523-532, 2001. (C) 2001 Wiley-Liss , Inc.