Discovery of baicalin and baicalein as novel, natural product inhibitors of SARS-CoV-2 3CL protease in vitro

Haixia Su; Sheng Yao; Wenfeng Zhao; Minjun Li; Jia Liu; Weijuan Shang; Hang Xie; Changqiang Ke; Meina Gao; Kunqian Yu; Hong Liu; Jingshan Shen; Wei Tang; Leike Zhang; Jianping Zuo; Hualiang Jiang; Fang Bai; Yan Wu; Yang Ye; Yechun Xu

Native state electrospray ionization mass spectrometry (ESI-MS) has been used extensively to directly observe native state proteins and protein complexes, allowing direct detection of protein-ligand non-covalent complexes with Kds as weak as 1 mM (16) . The determination of m/z between [protein + ligand] m/z and [unbound protein] m/z is able to identify a ligand as a binder with the correct molecular weight, while the ratio of the intensity of the [protein + ligand] peaks relative to [unbound protein] peaks provides a qualitative indication of the ligand-binding affinity. Herein, an ESI-MS analysis using high-resolution magnetic resonance mass spectrometry (MRMS) was carried out to detect the binding of baicalin and baicalein with SARS-CoV-2 3CLpro. For the free protease performance optimization, the mass range around the change stated 18+ was isolated with a center mass of the quadrupole of m/z 3750 (Fig. S3 ).