19 derivatives of 1-benzyl-3-arylpyrazole-5-carboxamides (H1-H19) and 5 derivatives of 1-benzyl-5-arylpyrazole-3-carboxamides (J1-J5) have been designed and synthesized as potential negative allosteric modulators (NAMs) for the β2-adrenergic receptor (β2AR). The new pyrazole derivatives were screened on the classic G-protein dependent signaling pathway at β2AR. The majority of 1-benzyl-3-aryl-pyrazole-5-carboxamide derivatives show more potent allosteric antagonistic activity against β2AR than Cmpd-15, the first reported β2AR NAM. However, the 1-benzyl-5-arylpyrazole-3-carboxamide derivatives exhibit very poor or even no allosteric antagonistic activity for β2AR. Furthermore, the active pyrazole derivatives have relative better drug-like profiles than Cmpd-15. Taken together, we discovered a series of derivatives of 1-benzyl-3-arylpyrazole-5-carboxamides as a novel scaffold of β2AR NAM.

The β2-adrenergic receptor (β2AR), a G protein-coupled receptor, is an important therapeutic target. We recently described Cmpd-15, the first small molecule negative allosteric modulator (NAM) for the β2AR. Herein we report in details the design, synthesis and structure-activity relationships (SAR) of seven Cmpd-15 derivatives. Furthermore, we provide in a dose-response paradigm, the details of the effects of these derivatives in modulating agonist-induced β2AR activities (G-protein-mediated cAMP production and β-arrestin recruitment to the receptor) as well as the binding affinity of an orthosteric agonist in radio-ligand competition binding assay. Our results show that some modifications, including removal of the formamide group in the para-formamido phenylalanine region and bromine in the meta-bromobenzyl methylbenzamide region caused dramatic reduction in the functional activity of Cmpd-15. These SAR results provide valuable insights into the mechanism of action of the NAM Cmpd-15 as well as the basis for future development of more potent and selective modulators for the β2AR based on the chemical scaffold of Cmpd-15.