Resolution, absolute stereochemistry, and pharmacology of the S-(+)- and R-(-)-isomers of the apparent partial AMPA receptor agonist (R,S)-2-amino-3-(3-hydroxy-5-phenylisoxazol-4-yl)propionic acid [(R,S)-APPA].
(R,S)-2-Amino-3-(3-hydroxy-5-phenylisoxazol-4-yl)propionic acid ((R,S)-APPA) is the only partial agonist at the (R,S)-2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA) subtype of excitatory amino acid receptors so far described. In light of the pharmacological interest in partial agonists, we have now accomplished the resolution of (R,S)-APPA. (S)-(+)-APPA (5) and (R)-(-)-APPA (6) were obtained in high enantiomeric purity using (R)-(+)- and (S)-(-)-1-phenylethylamine, respectively, as resolving agents. The absolute stereochemistry of 6 was established by X-ray analysis of 6.HCl.0.25H2O. Compounds 5 and 6 were tested electropharmacologically using the rat cortical wedge preparation and in receptor-binding assays using [3H]-AMPA, [3H]kainic acid, and the N-methyl-D-aspartic acid (NMDA) receptor ligands [3H]CPP, [3H]MK-801, and [3H]glycine. Whereas 6 did not significantly affect the binding of any of these ligands (IC50 > 100 microM), compound 5 revealed affinity for only the [3H]AMPA-binding site (IC50 = 6 microM). In electropharmacological tests, 5 showed full AMPA receptor agonism (EC50 = 230 microM). This effect of 5 was insensitive to the NMDA antagonist CPP but was inhibited competitively by the non-NMDA antagonist NBQX (pKi = 6.30). Compound 6, on the other hand, turned out to be a non-NMDA receptor antagonist, inhibiting competitively depolarizations induced by AMPA (pKi = 3.54), kainic acid (pKi = 3.07), and 5 (pKi = 3.57).
Ebert
B
B
PharmaBiotec Research Center, Department of Organic Chemistry, Royal Danish School of Pharmacy, Copenhagen.
Lenz
S
S
Brehm
L
L
Bregnedal
P
P
Hansen
J J
JJ
Frederiksen
K
K
Bøgesø
K P
KP
Krogsgaard-Larsen
P
P
D000409:Alanine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism; D018360:Crystallography, X-Ray; D016291:Dizocilpine Maleate / Q000378:metabolism; D005998:Glycine / Q000378:metabolism; D066298:In Vitro Techniques; D007555:Isoxazoles / Q000737:chemistry* / Q000494:pharmacology; D007608:Kainic Acid / Q000378:metabolism; D051381:Rats; D018091:Receptors, AMPA / Q000037:antagonists & inhibitors* / Q000378:metabolism; D013237:Stereoisomerism; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid / Q000378:metabolism
D007555:Isoxazoles; D018091:Receptors, AMPA; C086714:2-amino-3-(3-hydroxy-5-phenylisoxazol-4-yl)propionic acid; D016291:Dizocilpine Maleate; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; D000409:Alanine; D007608:Kainic Acid; D005998:Glycine