Synthesis and biological evaluation of β2-adrenoceptor agonists bearing the 2-amino-2-phenylethanol scaffold.

A new series of β2-adrenoceptor agonists bearing the 2-amino-2-phenylethanol scaffold was synthesized. Evaluation of the compounds using cell assays and an in vitro guinea pig trachea relaxation assay showed that 8-hydroxy-5-(2-hydroxy-1-((4-hydroxyphenethyl)amino)ethyl)quinolin-2(1H)-one (compound 5j) has the best pharmacological profile among all the evaluated compounds. The (S)-isomer of 5j was subsequently found to be the active enantiomer with a promising EC50 value of 1.26 nM in stimulating β2-adrenoceptor-mediated cAMP accumulation and a substantially higher selectivity for the β2 than for the β1 subtype. The putative binding mode of (S)-5j revealed by molecular docking of the β2-adrenoceptor resembles that in agonist binding. Taken together, these results showed that compound (S)-5j is a promising compound worthy of further study for the development of β2-adrenoceptor agonists.