Design, synthesis and activity evaluation of 4-(quinoline-2-yl)aniline derivatives as SARS-CoV‑2 main protease inhibitors

Since 2020, numerous compounds have been investigated for their potential use in treating SARS-CoV-2 infections. By identifying the molecular targets during the virus replication process, rationally designed anti-SARS-CoV-2 agents are developed. Among these targets, the main protease (M^pro) is a crucial enzyme required for virus replication, and its highly conserved characteristic make it an important drug target for the development of anti-SARS-CoV-2 drugs. Herein, we utilized warhead-based design strategy to conduct the structural optimization of M-1 developed through virtual screening, leading to a series of novel M^pro inhibitors with 4-(quinolin-2-yl)aniline scaffold. Among them, M-32 exhibited good SARS-CoV-2 M^pro inhibitory activity (IC₅₀ = 5.2 μM) with a nearly 25-fold increase. Isothermal titration calorimetry (ITC) directly proved that M-32 binds directly to SARS-CoV-2 M^pro in an entropy-driven manner. Mass spectrometry (MS) further confirmed the covalent binding ability of M-32 to M^pro. Meanwhile, M-32 effectively inhibited the replication of SARS-CoV-2 in Vero E6 cells (EC₅₀ = 5.29 μM).