For good b₂-receptor agonist selectivity there are three distinct structural features:

1. A modified m-OH function such as –CH₂OH (albuterol), -NHR (soterenol), etc. all of these modified groups are still able to hydrogen bond to the receptor in a manner similar to the m-phenolic OH group of the catechol function of the norepinephrine. Perhaps this structural modification resulted in a compound that is unable to bind the b1 receptor to elicit an agonist response.
2. A second unique structural modification is shifting the para phenolic OH group of the catechol moiety of the norepinephrine into the other meta position to give a compound with two m-OH groups (metaproterenol, bambuterol, or terbutaline). Again, this arrangement resulted in a compound that is unable to bind the b₁ receptors.
3. The third structural feature is the substitution of a small alkyl group (methyl or ethyl) on the a-carbon next to the amine function (Ritodrine, isoetharine).

Note: Replacement of the isopropyl group with tertiary butyl group only slightly favors binding to the b₂ receptors. Thus, colterol has more b₂ activity than b₁ activity.

For b₁ selective agonists:

The only structural feature seems to be the presence of an additional oxygen atom inserted between the aromatic ring and the side chain (prenalterol, tazolol). Both of these compounds also lack the m-OH group. Thus, the m-OH appears to be essential for the binding of b₂ receptors.