The design, synthesis and pharmacological characterization of novel β₂-adrenoceptor antagonists

Selective and potent antagonists for the β(2) -adrenoceptor are potentially interesting as experimental and clinical tools, and we sought to identify novel ligands with this pharmacology.

A range of pharmacological assays was used to assess potency, affinity, selectivity (β(2) -adrenoceptor vs. β(1) -adrenoceptor) and efficacy.

Ten novel compounds were identified but none had as high affinity as the prototypical β(2) -adrenoceptor blocker ICI-118,551, although one of the novel compounds was more selective for β(2) -adrenoceptors. Most of the ligands were inverse agonists for β(2) -adrenoceptor-cAMP signalling, although one (5217377) was a partial agonist and another a neutral antagonist (7929193). None of the ligands were efficacious with regard to β(2) -adrenoceptor-β-arrestin signalling. The (2S,3S) enantiomers were identified as the most active, although unusually the racemates were the most selective for the β(2) -adrenoceptors. This was taken as evidence for some unusual enantiospecific behaviour.

In terms of improving on the pharmacology of the ligand ICI-118,551, one of the compounds was more selective (racemic JB-175), while one was a neutral antagonist (7929193), although none had as high an affinity. The results substantiate the notion that β-blockers do more than simply inhibit receptor activation, and differences between the ligands could provide useful tools to investigate receptor biology.