Rational Designof Azaindole Derivatives via a Nitrogen-WalkStrategy from β-Carboline: Discovery of Highly Selective,Low-Toxicity URAT1 Inhibitors as Potent Urate-Lowering Agents

Abstract Hyperuricemia-induced gout is largely driven by impaired renal urate excretion, while current URAT1 inhibitors suffer from OAT1-mediated off-target toxicity. Our lead compound E1 potently inhibited URAT1 (IC50 = 3.02 μM) and reduced serum uric acid but exhibited OAT1 inhibition (IC50 = 4.78 μM) and HK-2 cytotoxicity (CC50 = 46.22 μM). To improve selectivity while retaining the core pharmacophore, a nitrogen-walk strategy was applied to design 48 azaindole derivatives. Pyrrolo[3,2-d]pyrimidine-based compound 17 was identified as the optimized candidate, exhibiting URAT1 inhibition (IC50 = 5.32 μM) with reduced OAT1 inhibition (IC50 = 30.11 μM), achieving a 6.7-fold selectivity improvement over E1. Compound 17 reduced serum uric acid by 77.7% at 2 mg/kg in an acute hyperuricemia mouse model and alleviated hepatic and renal injury in a chronic hyperuricemia model. It exhibited favorable druggability, including 87.9% oral bioavailability, a minimum effective dose below 0.5 mg/kg, and no observable toxicity up to 1000 mg/kg.