Discovery, Optimization, and Evaluation of Quinazolinone Derivatives with Novel Linkers as Orally Efficacious Phosphoinositide-3-Kinase Delta Inhibitors for Treatment of Inflammatory Diseases

Guided by molecular docking, a commonly used open-chain linker was cyclized into a five-membered pyrrolidine to lock the overall conformation of the propeller-shaped molecule. Different substituents were introduced into the pyrrolidine moiety to block oxidative metabolism. Surprisingly, it was found that a small methyl substituent could be used to alleviate the oxidative metabolism of pyrrolidine while maintaining or enhancing potency, which could be described as a “magic methyl”. Further optimization around the “3rd blade” of the propeller led to identification of a series of potent and selective PI3Kδ inhibitors. Among them, compound 50 afforded an optimum balance of PK profiles and potency. Oral administration of 50 attenuated the arthritis severity in a dose-dependent manner in a collagen-induced arthritis model without obvious toxicity. Furthermore, 50 demonstrated excellent pharmacokinetic properties with high bioavailability, suggesting that 50 might be an acceptable candidate for treatment of inflammatory diseases.