The Importance of Hydrogen Bonding and Aromatic Stacking to the Affinity and Efficacy of Cannabinoid Receptor CB₂ Antagonist, 5‑​(4-​chloro-​3-​methylphenyl)-​1-​[(4-​methylphenyl)methyl]‑​<i>N</i>‑​[(1<i>S</i>,​2<i>S</i>,​4<i>R</i>)‑​1,​3,​3-​trimethylbicyclo[2.2.1]hept-​2-​yl]-​1H-​pyrazole-​3-​carboxamide (SR144528)

Abstract

Despite the therapeutic promise of the subnanomolar affinity cannabinoid CB₂ antagonist, 5-​(4-​chloro-​3-​methylphenyl)-​1-​[(4-​methylphenyl)­methyl]-<i>​N</i>-​[(1<i>S</i>,​2<i>S</i>,​4<i>R</i>)-​1,​3,​3-​trimethylbicyclo­[2.2.1]­hept-​2-​yl]-​1<i>H</i>-​pyrazole-​3-​carboxamide (SR144528, <b>1</b>), little is known about its binding site interactions and no primary interaction site for <b>1</b> at CB2 has been identified. We report here the results of Glide docking studies in our cannabinoid CB₂ inactive state model that were then tested via compound synthesis, binding, and functional assays. Our results show that the amide functional group of <b>1</b> is critical to its CB2 affinity and efficacy and that aromatic stacking interactions in the TMH5/6 aromatic cluster of CB2 are also important. Molecular modifications that increased the positive electrostatic potential in the region between the fenchyl and aromatic rings led to more efficacious compounds. This result is consistent with the EC-3 loop negatively charged amino acid, D275 (identified via Glide docking studies) acting as the primary interaction site for <b>1</b> and its analogues