Resolution, absolute stereochemistry, and enantiopharmacology of the GluR1-4 and GluR5 antagonist 2-amino-3-[5-tert-butyl-3-(phosphonomethoxy)-4-isoxazolyl]propionic acid

The phosphono amino acid, (RS)-2-amino-3-[5-tert-butyl-3-(phosphonomethoxy) -4-isoxazolyl] propionic acid (ATPO), is a structural hybrid between the NM DA antagonist (RS)-2-amino-7-phosphonoheptanoic acid (AP7) and the AMPA and GluR5 agonist, (RS)-2-amino-3-(5-tert-butyl-3-hydroxy-4-isoxazolyl) propio nic acid (ATPA). ATPO has been resolved into (S)-ATPO and (R)-ATPO using ch iral HPLC, and the absolute stereochemistry of the two enantiomers was esta blished by an X-ray crystallographic analysis of (R)-ATPO. (S)-ATPO and (R) -ATPO were characterized pharmacologically using rat brain membrane binding and electrophysiologically using the cortical wedge preparation as well as homo- or heteromeric GluR1-4, GluR5-6, and KA2 receptors expressed in Xeno pus oocytes. (R)-ATPO was essentially inactive as an agonist or antagonist in all test systems. (S)-ATPO was an inhibitor of the binding of [H-3]AMPA (IC50 = 16 +/- 1 mu M) and of [H-3]-6-cyano-7-nitroquinoxaline-2,3-dione ([ H-3]CNQX) (IC50 = 1.8 +/- 0.2 mu M), but was inactive in the [H-3]kainic ac id and the [H-3]-(RS)-3-(2-carboxypiperazin-4-yl) propyl-1-phosphonic acid ([H-3]CPP) binding assays. (S)-ATPO did not show detectable agonist effects at any of the receptors under study, but antagonized AMPA-induced depolari zation in the cortical wedge preparation (IC50 = 15 +/- 1 mu M). (S)-ATPO a lso blocked kainic acid agonist effects at GluR1 (K-i = 2.0 mu M), GluR1+2 (K-i = 3.6 mu M), GluR3 (K-i = 3.6 mu M), GluR4 (K-i = 6.7 mu M), and GluR5 (K-i = 23 mu M), but was inactive at GluR6 and GluR6+KA2. Thus, although A TPO is a structural analog of AP7 neither (S)-ATPO nor (R)-ATPO are recogni zed by NMDA receptor sites. Chirality 11:752-759, 1999. (C) 1999 Wiley-Liss , Inc.