Integrated Synthetic, Pharmacological, and Computational Investigation of cis‐2‐(3,5‐Dichlorophenylcarbamoyl)cyclohexanecarboxylic Acid Enantiomers As Positive Allosteric Modulators of Metabotropic Glutamate Receptor Subtype 4

Abstract

2-(3,5-Dichlorophenylcarbamoyl)cyclohexanecarboxylic acid (1) is a potent and selective positive allosteric modulator of metabotropic glutamate receptor subtype 4 (mGluR4). The activity of 1 was reported to reside in the cis diastereomer with equal potency between its enantiomeric forms (Niswender et al., Mol. Pharmacol. 2008, 74, 1345-1358). In the present study, the asymmetric synthesis of each of the cis enantiomers was performed, and their activities were compared with that of the racemic trans. In our assays, the cis enantiomers differ in potency, with one of them (1R,2S) higher and the other (1S,2R) lower than the racemic trans. High-level quantum chemical calculations were carried out to characterize the structures of minimum energy in all-isomer conformational space as well as particular intermediates between conformational transitions. Computational analysis identified structural features of 1 that can play a role in mGluR4 functionality and establish the basis for subsequent work, in which molecular chirality constructed on conformations derived from those found for the active (1R,2S) enantiomer can provide new ideas for drug discovery. Comparison between experimental and theoretical circular dichroism spectra confirmed both the absolute configuration of the (1R,2S) compound and its calculated most stable conformation, thereby supporting experimental and theoretical work.

Recent Progress on the Identification of Metabotropic Glutamate 4 Receptor Ligands and Their Potential Utility as CNS Therapeutics

“…However, this was later hypotheized to be due to an unusual racemization reaction, as resynthesis of the enantiomers by an independent group showed the activity to reside solely with one enantiomer ((1R, 2S)-15). 51 The SAR reported for this series was unremarkable, as little change was tolerated in various domains of the scaffold. 52 Interestingly, 15 has only partial agonist activity in the mGlu4 assay and does not compete with PHCCC binding.…”

Exploring the Active Conformation of Cyclohexane Carboxylate Positive Allosteric Modulators of the Type 4 Metabotropic Glutamate Receptor

“…However, the rich conformational flexibility of the cyclohexane ring and the VU0155041 enantiomer distinction at the receptor represent an attractive platform to study the structural and functional features of allosteric potentiation at the mGlu 4 receptor. In this context, the different activities between the cis-rac-2 (EC 50 : 2.8 mm) and trans-rac-3 (EC 50 : 22.0 mm) diastereomers, and the differential activity found for the enantiomers [13] of 2 (1R,2S)-2 (EC 50 : 0.8 mm) and (1S,2R)-2 (EC 50 > 100 mm) appear to define a very specific interaction of these ligands with the mGlu 4 receptor. The presence of 1,2-disubstitution in these compounds delineates different conformations which, in the case of the more stable chair conformers, can place the groups in either axial or equatorial arrangement.…”

“…nally reported, [10] the two VU0155041 enantiomers differed in pharmacological activity, with (1R,2S)-2 being more potent than (1S,2R)-2. [13] In addition, two conformations for each of the cis-VU0155041 and trans-VU0155040 diastereomers were characterized by high-level quantum mechanical (QM) calculations. The enantioselective nature of recognition of this family in the mGlu 4 receptor was consistently confirmed with the structurally related cis-1,2-cyclohexanediamides, [14] with the (1S,2R) Lu AF21934 enantiomer more active than the (1R,2S) Lu AF21935 enantiomer.…”

“…In the mGlu 4 PAM trans-cyclohexane 3, we found that diaxial conformer was energetically disfavored by 6.96 kcal mol À1 . [13] In contrast, the cis-1,2-cyclohexane arrangement defines two chair conformers having one substituent in an axial position and the other in an equatorial position. In our previous report, [13] we found a low difference in energy (~0.9 kcal mol À1 ) between the two conformations of the compound tested, both under vacuum and in the hydrophobic and hydrophilic condensed media, which gives both conformations a similar probability to compete for the receptor binding site.…”

“…[13] In contrast, the cis-1,2-cyclohexane arrangement defines two chair conformers having one substituent in an axial position and the other in an equatorial position. In our previous report, [13] we found a low difference in energy (~0.9 kcal mol À1 ) between the two conformations of the compound tested, both under vacuum and in the hydrophobic and hydrophilic condensed media, which gives both conformations a similar probability to compete for the receptor binding site. In the present work, we studied some of the structural features of the cyclohexane carboxylate PAMs binding to the mGlu 4 receptor by using different probe molecules.…”