4-Alkyl- and 4-Cinnamylglutamic Acid Analogues Are Potent GluR5 Kainate Receptor Agonists

Enantiomerically pure (2S,4R)-4-substituted glutamic acids were prepared and tested for homomeric GluR5 and GluR6 kainate subtype receptor affinity. Some of the 4-cinnamyl analogues showed high selectivity and potency (K_i < 25 nM) for the GluR5 receptors. The greatest selectivity and potency were achieved with the 3-(2-naphthyl)prop-2-enyl compound. This compound, LY339434, has negligible activity at the AMPA and kainate receptors GluR1, -2, -4 and -6. Although, LY339434 shows agonist activity at NMDA receptors in cultural hippocampal neurons (approximate EC₅₀ of 2.5 μM), we consider that LY339434 should be a useful pharmacological tool for the investigation of the functional role of GluR5 kainate receptors.