Cycloalkyl indole-2-carboxylates as useful tools for mapping the "north-eastern" region of the glycine binding site associated with the NMDA receptor.

A novel series of indole-2-carboxylate analogues of GV 150526 (1) in which the terminal phenyl ring belonging to the side chain present in the position C-3 has been replaced with a bridged cycloalkyl group was synthesized and evaluated for its pharmacological profile. Modelling studies on this class of novel glycine antagonist allowed us to identify an asymmetric lipophilic pocket present in the "North-Eastern" region of the pharmacophoric model of the glycine binding site associated to the NMDA receptor. Among the derivatives prepared, 3-[2-(1-adamantylaminocarbonyl)ethenyl]-4,6-dichloroindole-2 -carboxylic acid 6b and 3-[2-(norbornylaminocarbonyl)ethenyl]-4,6-dichloroindole-2-c arboxylic acid 6l were found to be antagonists acting at the strychnine-insensitive glycine binding site, showing nanomolar affinity for the glycine binding site (Ki = 63 and 19 nM, respectively), coupled with high glutamate receptor selectivity (IC50 > 10(-5) M at the NMDA, AMPA, KA binding sites) and high in vivo potency after systemic administration by inhibition of convulsion induced by NMDA in mice.

New synthesis of substituted 2-carboxyindole derivatives: versatile introduction of a carbamoylethynyl moiety at the C-3 position.

A novel series of 3-carbamoylethynyl-2-carboxyindoles, antagonists acting at the strychnine-insensitive glycine binding site associated with the NMDA receptor, has been synthesised. This new versatile approach involves the introduction of a 2-chloroethenyl moiety in position C-3 with subsequent derivatisation of the terminal carboxyl group, followed by an unusual elimination of HCl to afford the ethynyl functionality. This novel series of glycine antagonists was evaluated in terms of in vitro affinity at the glycine binding site and the most potent compound was tested in vivo in the NMDA-induced convulsions model in mice.

Substituted indole-2-carboxylates as in vivo potent antagonists acting as the strychnine-insensitive glycine binding site.

A series of indole-2-carboxylates bearing suitable chains at the C-3 position of the indole nucleus was synthesized and evaluated in terms of in vitro affinity using [3H]glycine binding assay and in vivo potency by inhibition of convulsions induced by N-methyl-D-aspartate (NMDA) in mice. 3-[2-[(Phenylamino)carbonyl]ethenyl]-4,6-dichloroindole-2-carboxyl ic acid (8) was an antagonist at the strychnine-insensitive glycine binding site (noncompetitive inhibition of the binding of [3H]TCP, pA2 = 8.1) displaying nanomolar affinity for the glycine binding site (pKi = 8.5), coupled with high glutamate receptor selectivity (> 1000-fold relative to the affinity at the NMDA, AMPA, and kainate binding sites). This indole derivative inhibited convulsions induced by NMDA in mice, when administered by both iv and po routes (ED50 = 0.06 and 6 mg/kg, respectively). The effect of the substituents on the terminal phenyl ring of the C-3 side chain was investigated. QSAR analysis suggested that the pKi value decreases with lipophilicity and steric bulk of substituents and increases with the electron donor resonance effect of the groups present in the para position of the terminal phenyl ring. According to these results the terminal phenyl ring of the C-3 side chain should lie in a nonhydrophobic pocket of limited size, refining the proposed pharmacophore model of the glycine binding site associated with the NMDA receptor.