Synthesis and Biological Evaluation of 1-Amino-2-Phosphonomethylcyclopropanecarboxylic Acids, New Group III Metabotropic Glutamate Receptor Agonists

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Abstract
Stereoisomers of 1-amino-2-phosphonomethylcyclopropanecarboxylic acid (APCPr), conformationally restricted analogues of l-AP4 (2-amino-4-phosphonobutyric acid), have been prepared and evaluated at recombinant group III metabotropic glutamate receptors. They activate these receptors over a broad range of potencies. The most potent isomer (1S,2R)-APCPr displays a similar pharmacological profile as that of l-AP4 (EC50 0.72, 1.95, >500, 0.34 μM at mGlu4, 6, 7, 8 receptors, respectively, and no effect at group I/II mGluRs). It was characterized on native receptors located in the basal ganglia (BG) where it induced a robust and reversible inhibition of synaptic transmission. It was tested in vivo in haloperidol-induced catalepsy, a model of Parkinsonian akinesia, by direct infusion in the globus pallidus of the BG. At a dose of 0.5 nmol/μL, catalepsy was significantly antagonized. This study reveals that (1S,2R)-APCPr is a potent group III mGluR agonist and confirms that these receptors may be considered as a therapeutic target in the Parkinson's disease.