N-methyl-D-aspartic acid receptor agonists: resolution, absolute stereochemistry, and pharmacology of the enantiomers of 2-amino-2-(3-hydroxy-5-methyl-4-isoxazolyl)acetic acid.
(R,S)-2-Amino-2-(3-hydroxy-5-methyl-4-isoxazolyl)acetic acid [(R,S)-AMAA, 4] is a potent and selective agonist at the N-methyl-D-aspartic acid (NMDA) subtype of excitatory amino acid receptors. Using the Ugi "four-component condensation" method, the two diastereomers (2R)- and (2S)-2-[3-(benzyloxy)-5-methyl-4-isoxazolyl]N-tert-butyl-2- [N-[(S)-1-phenylethyl]benzamido]-acetamide (16 and 17, respectively) were synthesized and separated chromatographically. The absolute stereochemistry of 16 was confirmed by an X-ray analysis. Deprotection of these intermediates did, however, provide (R)- (8) and (S)- (9) AMAA, respectively, in extensively racemized forms. N-BOC-protected (R,S)-AMAA (21) was successfully resolved via diastereomeric salt formation using cinchonidine. The stereochemical purity and stability of 8 and 9 obtained via this resolution were determined using chiral HPLC. (R)-AMAA (8) showed peak affinity for [3H]AMPA receptor sites (IC50 = 72 +/- 13 microM) and was shown to be a more potent inhibitor of [3H]CPP binding (IC50 = 3.7 +/- 1.5 microM) than (S)-AMAA (9) (IC50 = 61 +/- 6.4 microM). Neither enantiomer of AMAA affected [3H]kainic acid receptor binding significantly. In electrophysiological studies using rat brain tissue, 8 (EC50 = 7.3 +/- 0.3 microM) was 1 order of magnitude more potent than 9 (EC50 = 75 +/- 9 microM) as an NMDA receptor agonist.
Madsen
U
U
Department of Medicinal Chemistry, Royal Danish School of Pharmacy, Copenhagen, Denmark.
Frydenvang
K
K
Ebert
B
B
Johansen
T N
TN
Brehm
L
L
Krogsgaard-Larsen
P
P
D000085:Acetates / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D000818:Animals; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D002851:Chromatography, High Pressure Liquid; D018360:Crystallography, X-Ray; D004594:Electrophysiology; D018690:Excitatory Amino Acid Agonists / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D006860:Hydrogen Bonding; D066298:In Vitro Techniques; D007555:Isoxazoles / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D015394:Molecular Structure; D051381:Rats; D018091:Receptors, AMPA / Q000378:metabolism; D018092:Kainic Acid Receptors / Q000378:metabolism; D016194:Receptors, N-Methyl-D-Aspartate / Q000819:agonists* / Q000378:metabolism; D013237:Stereoisomerism
D000085:Acetates; D018690:Excitatory Amino Acid Agonists; D007555:Isoxazoles; D018091:Receptors, AMPA; D018092:Kainic Acid Receptors; D016194:Receptors, N-Methyl-D-Aspartate; C089706:2-amino-2-(3-hydroxy-5-methyl-4-isoxazolyl)acetic acid