Design, synthesis and biological evaluation of quinazoline-based covalent PI3Kδ inhibitors targeting Lys779 residue

Phosphoinositide 3-kinase δ (PI3Kδ) is a clinically validated therapeutic target for hematological malignancies, while selective covalent inhibition provides an attractive strategy for achieving sustained PI3Kδ suppression. Herein, a series of quinazoline-based covalent PI3Kδ inhibitors bearing lysine-reactive warheads were designed and synthesized to target Lys779 residue in the pocket of PI3Kδ. Compound C1 bearing a 2,4-difluorophenolic ester warhead, exhibited the most potent PI3Kδ inhibition with an IC₅₀ value of 0.05 nM and > 150-fold selectivity over other class I PI3K isoforms in vitro. C1 exerted robust antiproliferative activity against SU-DHL-6 cells (GI₅₀ = 0.025 μM), and mechanistic investigation revealed that C1 significantly induced apoptosis in a concentration-dependent manner. Washout assay demonstrated that C1 retained the sustained antiproliferative activity against SU-DHL-6 cells after drug removal. Docking simulation suggested a plausible covalent binding occurred and a stable covalent bond formed between the warhead 2,4-difluorophenolic ester of C1 with Lys779 through ester aminolysis in the pocket of PI3Kδ. This research highlights the scope of lysine-targeting covalent design and lays a solid foundation for the development of novel potent irreversible PI3Kδ inhibitors.