We previously discovered that indazole derivative 8 was a highly selective β-adrenergic receptor (β-AR) agonist, but it appeared to be metabolically unstable. To improve metabolic stability, further optimization of this scaffold was carried out. We focused on the sulfonamide moiety of this scaffold, which resulted in the discovery of compound 15 as a highly potent β-AR agonist (EC = 18 nM) being inactive to β-, β-, and α-AR (β/β, β/β, and α/β > 556-fold). Compound 15 showed dose-dependent β-AR-mediated responses in marmoset urinary bladder smooth muscle, had a desirable metabolic stability and pharmacokinetic profile (C and AUC), and did not obviously affect heart rate or mean blood pressure when administered intravenously (3 mg/kg) to anesthetized rats. Thus, compound 15 is a highly potent, selective, and orally available β-AR agonist, which may serve as a candidate drug for the treatment of overactive bladder without off-target-based cardiovascular side effects.
Novel indazole derivatives were prepared and evaluated for their biological activity and cardiovascular safety profile as human β3-adrenergic receptor (AR) agonists. Although the initial hit compound 5 exhibited significant β3-AR agonistic activity (EC50 = 21 nM), it also exhibited agonistic activity at the α1A-AR (EC50 = 219 nM, selectivity: α1A/β3 = 10-fold). The major metabolite of 5, which was an oxidative product at the indazole 3-methyl moiety, gave a clue to a strategy for improvement of the selectivity for β3-AR agonistic activity versus α1A-AR agonistic activity. Thus, modification of the 3-substituent of the indazole moiety effectively improved the selectivity to develop compound 11 with potent β3-AR agonistic activity (EC50 = 13 nM) and high selectivity (α1A/β3 = >769-fold). Compound 11 was also inactive toward β1 and β2-ARs and showed dose dependent β3-AR mediated relaxation of marmoset urinary bladder smooth muscle, while it did not obviously affect heart rate or blood pressure (iv, 3 mg/kg) in anesthetized rats.
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