Rational design and enantioselective synthesis of (1R,4S,5R,6S)-3-azabicyclo[3.3.0]octane-4,6-dicarboxylic acid - a novel inhibitor at human glutamate transporter subtypes 1, 2, and 3

The natural product kainic acid is used as template for the rational design of a novel conformationally restricted (S)-glutamic acid (Glu) analogue, (1R,4S,5R,6S)-3-azabicyclo[3.3.0]octane-4,6-dicarboxylic acid (1a). The target structure 1a was synthesized from commercially available (S)-pyroglutaminol, in an enantioselective fashion, in 14 steps. Pharmacological characterization of 1a at human glutamate transporter subtypes 1, 2, and 3 yielded K(i) values of 127, 52, and 46 microM, respectively. Furthermore, binding studies at native ionotropic Glu (iGlu) receptors revealed low affinity for alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)-preferring iGlu receptors (IC(50) > 100 microM), whereas affinities for the KAIN-preferring iGlu receptors and the N-methyl-d-aspartate (NMDA)-preferring group of iGlu receptors were in the low micromolar range (IC(50) = 14 and 2.9 microM, respectively). At metabotropic Glu receptors (mGluR), EC(50) values for 1a were >1000 microM for mGluR1 and 4, representing group I and III, respectively, and approximately 1000 microM (agonist) for mGluR2, representing group II.