Discovery of Novel Indazole Derivatives as Highly Potent and Selective Human β3-Adrenergic Receptor Agonists with the Possibility of Having No Cardiovascular Side Effects

Novel indazole derivatives were prepared and evaluated for their biological activity and cardiovascular safety profile as human A-adrenergic receptor (AR) agonists. Although the initial hit compound 5 exhibited significant beta(3)-AR agonistic activity (EC50 = 21 nM), it also exhibited agonistic activity at the alpha(1A)-AR (EC50 = 219 nM, selectivity: alpha(1A)/beta(3) = 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 beta(3)-AR agonistic activity versus au-AR agonistic activity. Thus, modification of the 3-substituent of the indazole moiety effectively improved the selectivity to develop compound 11 with potent beta(3)-AR agonistic activity (EC50 = 13 nM) and high selectivity (alpha(1A)/beta(3) = >769-fold). Compound 11 was also inactive toward beta(1) and beta(2)-ARs and showed dose dependent beta(3)-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.