Amino diacid 3, a highly selective competitive GluR5 kainate receptor antagonist, exhibited high GluR5 receptor affinity and selectivity over other glutamate receptors. Its diethyl ester prodrug 4 was orally active in two models of migraine: the neurogenic dural plasma protein extravasation model and the nucleus caudalis c-fos expression model. These data suggest that a GluR5 kainate receptor antagonist might be an efficacious antimigraine therapy with a novel mechanism of action.

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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 EC(50) of 2.5 microM), we consider that LY339434 should be a useful pharmacological tool for the investigation of the functional role of GluR5 kainate receptors.

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Amino acids 5 and 7, two potent and selective competitive GluR5 KA receptor antagonists, exhibited high GluR5 receptor affinity over other glutamate receptors. Their ester prodrugs 6 and 8 were orally active in three models of pain: reversal of formalin-induced paw licking, carrageenan-induced thermal hyperalgesia, and capsaicin-induced mechanical hyperalgesia.

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