SYNTHESIS OF THE 4 ISOMERS OF 4-AMINOPYRROLIDINE-2,4-DICARBOXYLATE - IDENTIFICATION OF A POTENT, HIGHLY SELECTIVE, AND SYSTEMICALLY-ACTIVE AGONIST FOR METABOTROPIC GLUTAMATE RECEPTORS NEGATIVELY COUPLED TO ADENYLATE-CYCLASE

The four isomers of 4-aminopyrrolidine-2,4-dicarboxylate (APDC) were p repared and evaluated for their effects at glutamate receptors in vitr o. (2R,4R)-APDC (2a), an aza analog of the nonselective mGluR agonist (1S,3R)-1-aminocyclopentane-1,3-dicarboxylate ((1S,3R)-ACPD, 1), was f ound to possess relatively high affinity for metabotropic glutamate re ceptors (mGluRs) (ACPD-sensitive [H-3]glutamate binding IC50 = 6.49 +/ - 1.21 mu M) with no effects on radioligand binding to NMDA, AMPA, or kainate receptors up to 100 mu M. None of the other APDC isomers showe d significant mGluR binding affinity, indicating that this interaction is highly stereospecific. Both 1 and 2a were effective in decreasing forskolin-stimulated cAMP formation in the adult rat cerebral cortex ( EC(50) = 8.17 +/- 2.21 mu M for 1; EC(50) = 14.51 +/- 5.54 mu M for 2a ); however, while 1 was also effective in stimulating basal tritiated inositol monophosphate production in the neonatal rat cerebral cortex (EC(50) = 27.7 +/- 5.2 mu M), 2a (up to 100 mu M) was ineffective in s timulating phosphoinositide hydrolysis in this tissue preparation, fur ther supporting our previous observations that 2a is a highly selectiv e agonist for mGluRs negatively coupled to adenylate cyclase. Microele ctrophoretic application of either 1 or 2a to intact rat spinal neuron s produced an augmentation of AMPA-induced excitation (95 +/- 10% incr ease for 1, 52 +/- 6% increase for 2a). Intracerebral injection of 1 ( 400 nmol) produced characteristic limbic seizures in mice which are no t mimicked by 2a (200-1600 nmol, ic). However, the limbic seizures ind uced by 1 were blocked by systemically administered 2a in a dose-depen dent manner (EC(50) = 271 mg/kg, ip). It is concluded that (2R,4R)-APD C (2a) is a highly selective, systemically-active agonist of mGluRs ne gatively coupled to adenylate cyclase and that selective activation of these receptors in vivo can result in anticonvulsant effects.