Identification of novel 1,2,3-triazole isatin derivatives as potent SARS-CoV-2 3CLpro inhibitors via click-chemistry-based rapid screening

SARS-CoV-2 3-chymotrypsin-like protease (3CL(pro)) is considered an attractive target for the development of anti-COVID-19 agents due to its vital function. The N-substituted isatin derivative L-26 is a potential SARS-CoV-2 3CL(pro) inhibitor, but it has poor cell-based antiviral activity and high cytotoxicity. With L-26 as the lead compound, 58 isatin derivatives were prepared using click-chemistry-based miniaturized synthesis and their 3CL(pro) inhibitory activities were determined by a fluorescence resonance energy transfer-based enzymatic assay. Compounds D1N8 (IC50 = 0.44 +/- 0.12 mu M) and D1N52 (IC50 = 0.53 +/- 0.21 mu M) displayed excellent inhibitory potency against SARS-CoV-2 3CL(pro), being equivalent to that of L-26 (IC50 = 0.30 +/- 0.14 mu M). In addition, the cytotoxicity of D1N8 (CC50 >20 mu M) and D1N52 (CC50 >20 mu M) decreased significantly compared with L-26 (CC50 <2.6 mu M). Further molecular dynamics simulations revealed the potential binding interactions between D1N52 and SARS-CoV-2 3CL(pro). These efforts lay a solid foundation for the research of novel anti-SARS-CoV-2 agents targeting 3CL(pro).