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 μM) and D1N52 (IC₅₀ = 0.53 ± 0.21 μM) displayed excellent inhibitory potency against SARS-CoV-2 3CL^pro, being equivalent to that of L-26 (IC₅₀ = 0.30 ± 0.14 μM). In addition, the cytotoxicity of D1N8 (CC₅₀ >20 μM) and D1N52 (CC₅₀ >20 μM) decreased significantly compared with L-26 (CC₅₀ <2.6 μM). 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.