(S)-2-Amino-3-(3-hydroxy-7,8-dihydro-6H-cyclohepta[d]isoxazol-4-yl)propionic acid, a potent and selective agonist at the GluR5 subtype of ionotropic glutamate receptors. Synthesis, modeling, and molecular pharmacology.
We have previously described (RS)-2-amino-3-(3-hydroxy-7,8-dihydro-6H-cyclohepta[d]isoxazol-4-yl)propionic acid (4-AHCP) as a highly effective agonist at non-N-methyl-d-aspartate (non-NMDA) glutamate (Glu) receptors in vivo, which is more potent than (RS)-2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA) but inactive at NMDA receptors. However, 4-AHCP was found to be much weaker than AMPA as an inhibitor of [(3)H]AMPA binding and to have limited effect in a [(3)H]kainic acid binding assay using rat cortical membranes. To shed light on the mechanism(s) underlying this quite enigmatic pharmacological profile of 4-AHCP, we have now developed a synthesis of (S)-4-AHCP (6) and (R)-4-AHCP (7). At cloned metabotropic Glu receptors mGluR1alpha (group I), mGluR2 (group II), and mGluR4a (group III), neither 6 nor 7 showed significant agonist or antagonist effects. The stereoisomer 6, but not 7, activated cloned AMPA receptor subunits GluR1o, GluR3o, and GluR4o with EC(50) values in the range 4.5-15 microM and the coexpressed kainate-preferring subunits GluR6 + KA2 (EC(50) = 6.4 microM). Compound 6, but not 7, proved to be a very potent agonist (EC(50) = 0.13 microM) at the kainate-preferring GluR5 subunit, equipotent with (S)-2-amino-3-(5-tert-butyl-3-hydroxyisothiazol-4-yl)propionic acid [(S)-Thio-ATPA, 4] and almost 4 times more potent than (S)-2-amino-3-(5-tert-butyl-3-hydroxyisoxazol-4-yl)propionic acid [(S)-ATPA, 3]. Compound 6 thus represents a new structural class of GluR5 agonists. Molecular modeling and docking to a crystal structure of the extracellular binding domain of the AMPA subunit GluR2 has enabled identification of the probable active conformation and binding mode of 6. We are able to rationalize the observed selectivities by comparing the docking of 4 and 6 to subtype constructs, i.e., a crystal structure of the extracellular binding domain of GluR2 and a homology model of GluR5.
Brehm
Lotte
L
Department of Medicinal Chemistry, The Danish University of Pharmaceutical Sciences, 2 Universitetsparken, DK-2100 Copenhagen, Denmark.
Greenwood
Jeremy R
JR
Hansen
Kasper B
KB
Nielsen
Birgitte
B
Egebjerg
Jan
J
Stensbøl
Tine B
TB
Bräuner-Osborne
Hans
H
Sløk
Frank A
FA
Kronborg
Tine T A
TT
Krogsgaard-Larsen
Povl
P
D000409:Alanine / Q000031:analogs & derivatives / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D018690:Excitatory Amino Acid Agonists / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D066298:In Vitro Techniques; D007555:Isoxazoles / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D008024:Ligands; D008958:Models, Molecular; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D009010:Monte Carlo Method; D009865:Oocytes / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D011422:Propionates / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D011869:Radioligand Assay; D018092:Kainic Acid Receptors / Q000819:agonists*; D017386:Sequence Homology, Amino Acid; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D014982:Xenopus laevis
D000409:Alanine; D018690:Excitatory Amino Acid Agonists; D007555:Isoxazoles; D008024:Ligands; D011422:Propionates; D018092:Kainic Acid Receptors; C473672:2-amino-3-(3-hydroxy-7,8-dihydro-6H-cyclohepta(d)isoxazol-4-yl)propionic acid