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]

Abstract

(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).

O-Methyl-4,5,6,7-tetrahydroisoxazolo[4,5-c]pyridin-3-ol Hydrochloride, O-Me-THPO.HCl

“…Crystal data (3) 112.8(2) 1.425 (3) 112.6(2) 1.420 (3) 112.9(2) References: AMIOXO, Brehm (1977); HAPIOX, Brehm & KrogsgaardLarsen (1974); HMUSCM, ISAZOL, Brehm & Larsen (1976); DECJAW/DECJAW01, Krogsgaard-Larsen et al (1985); DEVFEP, Brehm et al (1985); GASKUG, Madsen et al (1988); RSAMPA, Honor6 & Lauridsen (1980); SEBFUA, Hansen et al (1989); OPOXAZ/OPOXAZ01, Biagini et al (1969a,b); (R)-APPA, Ebert et al (1994).…”

“…As expected, the conjugation changes some of the geometric parameters, especially the C5---C4 and C4---C3 bonds. The compound (R)-APPA (Ebert et al, 1994) is included in Table 3 to show another compound with an extended conjugated system. The bond lengths show the same types of changes but they are not as pronounced in (R)-APPA as in OPOXAZ.…”

AMPA receptor agonists: Resolution, configurational assignment, and pharmacology of (+)-(S)- and (-)-(R)-2-amino-3-[3-hydroxy-5-(2-pyridyl)-isoxazol-4-yl]-propionic acid (2-Py-AMPA)

“…At this stage the first and the second eluting enantiomer showed enantiomeric purities of 99 and 97% ee, respectively, as determined by analytical chiral HPLC using the Chirobiotic T column. Recrystallization 25 For the determination of EAA-evoked depolarizations a previously described rat cortical wedge preparation was used. 25 …”

“…Recrystallization 25 For the determination of EAA-evoked depolarizations a previously described rat cortical wedge preparation was used. 25 …”

“…1) is a full AMPA receptor agonist, whereas (R)-APPA is a competitive AMPA receptor antagonist. 25,26 Thus, the partial AMPA receptor agonism of APPA is only apparent, and this observation has led us to introduce the pharmacological concept, functional partial agonism. 27,28 In order to develop this new pharmacological concept further we have synthesized the three pyridine analogues of APPA: (RS)-2-amino-3-[3-hydroxy-5-(2-pyridyl)isoxazol-4-yl]propionic acid (2-Py-AMPA), (RS)-2-amino-3-[3-hydroxy-5-(3-pyridyl)isoxazol-4-yl]propionic acid (3-Py-AMPA), and (RS)-2-amino-3-[3-hydroxy-5-(4-pyridyl)isoxazol-4-yl]propionic acid (4-Py-AMPA) (Fig.…”