Discovery of a Highly Selective β2‑Adrenoceptor Agonist with a 2‑Amino-2-phenylethanol Scaffold as an Oral Antiasthmatic Agent

Asthma patients in resource-poor countries cannot obtain adequate basic asthma medications because most asthma medications are supplied as inhalants. An alternative approach is to create oral antiasthmatic drugs with high β2/β1-selectivity, which should reduce treatment costs. In this study, we designed a cohort of compounds 1 using 2-(4-amino-3-chloro-5-(trifluoromethyl)­phenyl)-2-(tert-butylamino)­ethan-1-ol hydrogen chloride (1a) as the lead compound with an aim to expand the library of compounds possessing the 2-amino-2-phenylethanol scaffold. Structure–activity relationship studies on these compounds revealed that compounds created showed remarkable β2 selectivity compared to isoproterenol and gave additional insights on the rational design of β2-adrenoceptor agonists. Moreover, 1a was found as the best candidate compound showing the greatest potential for drug development. Cell-based assays showed that 1a was about 10 times more selective than salbutamol toward the β2-adrenoceptor. Moreover, 1a exhibited good oral bioavailability and low acute oral toxicity. These data reveal 1a as an oral antiasthmatic agent.