Identification of Buctopamine and Mebuctopamine, a β2 Receptor Agonist and Its Metabolite, in Swine Hair and Feed Additives

4-[2-(t-Butylamino)-1-hydroxyethyl]phenol (buctopamine, 4), a new β2 receptor agonist (β2-agonist), was found to be an adulterant in feed additives for swine in Taiwan, where using β2-agonists in food-production animals is prohibited. Buctopamine and its metabolite, 4-[2-(t-butylamino)-1-hydroxyethyl]-2-methoxyphenol (mebuctopamine, 2), were detected in swine hair specimens. Authentic compounds 2 and 4 were synthesized with 98.6% and 97.7% purity, respectively, as reference standards for analysis, and both compounds were more hydrophilic than ractopamine and clenbuterol. In a preliminary pharmacological evaluation, compounds 2 and 4 exhibited moderate human β2 receptor binding affinity and did not show significant affinities for the human α1, α2, β1, and β3 receptors. After addition of compounds 2–4 into the β2-agonist library, a multiresidue analysis of 26 β2-agonists by using triple quadrupole LC/MS/MS for routine screening conducted by regulatory authorities was established, in which the common limits ...