Biochemical activities of trimetoquinol analogs at human beta(1)- and beta(3)-adrenergic receptors

The biochemical activities of trimetoquinol (TMQ) analogs were evaluated at the human beta(1)- and beta(3)-adrenergic receptor (AR) subtypes expressed in Chinese hamster ovary cells. In radioligand binding assays, the 1-benzyl iodine-substituted analogs exhibited higher binding affinities at both beta(1)- and beta(3)-AR subtype as compared to TMQ. In cAMP accumulation assays, these analogs exhibited high potencies at both beta(1)- and beta(3)-AR. The 3',5'-diiodo-4'-amino analog of TMQ was the most potent beta(3)-AR agonist, 17-fold more potent at the beta(3)-AR versus the beta(1)-AR. Masking of the 6,7-dihydroxy group of the catechol ring of 3',5'-diiodo-4'-acetamido analog of TMQ, a potent beta(1)- and beta(3)-AR agonist, abolished activity at both beta-AR subtypes. Furthermore, substitution of a strong electron withdrawing group such as the trifluoromethyl moiety at the 1-benzyl ring of TMQ dramatically decreased potency at beta(1)- and beta(3)-AR compared to TMQ. Replacement of the 1-benzyl ring of TMQ with a naphthalene ring did not alter affinity but reduced potency of resulting 1-naphthylmethyl and 2-naphthylmethyl analogs at beta(1)- and beta(3)-AR compared to TMQ. Our results define the structural and electronic properties of substituents on TMQ necessary for potent activation of beta(1)- and beta(3)-AR and suggest that further modifications of the 1-benzyl iodine-substituted analogs may yield potent beta(3)-AR agonists.