Abstract Several carbostyril-based β-agonists have been shown to bind tightly to and slowly dissociate from the β 2-adrenoceptor (β 2 AR). In the present study, the structural features of 8-hydroxy-5-[2-[(1-phenyl-2-methylprop-2-yl) amino]-1-hydroxyethyl]-carbostyril (11a) which contribute to its binding properties at the β 2 AR were investigated using a series of synthesized analogs. The k off, estimated by the rate of cAMP decline in DDT 1 MF-2 (DDT ...