Design, Synthesis, and Biological Evaluation of Trisubstituted Piperazine Derivatives as Noncovalent Severe Acute Respiratory Syndrome Coronavirus 2 Main Protease Inhibitors with Improved Antiviral Activity and Favorable Druggability.

The ongoing transmission of SARS-CoV-2 necessitates the development of additional potent antiviral agents capable of combating the current highly infectious variants and future coronaviruses. Here, we present the discovery of potent nonpeptide main protease (M ^pro ) inhibitors with prominent antiviral activity and improved pharmacokinetic properties. Three series of 1,2,4-trisubstituted piperazine derivatives were designed and synthesized, and the optimal GC-78-HCl demonstrated high enzyme-inhibitory potency (IC ₅₀ = 0.19 μM) and exhibited excellent antiviral activity (EC ₅₀ = 0.40 μM), reaching the same level as Nirmatrelvir (EC ₅₀ = 0.38 μM). Additionally, GC-78-HCl displayed potent antiviral activities against various SARS-CoV-2 variants as well as HCoV-OC43 and HCoV-229E, indicating its potential broad-spectrum anticoronaviral activity. Notably, the pharmacokinetic properties of GC-78-HCl were somewhat enhanced compared to those of the lead compound. Furthermore, the cocrystal and molecular docking elucidated the mechanism of action. In conclusion, we discovered a novel nonpeptidic M ^pro inhibitor with promising antiviral activity and a favorable pharmacokinetic profile.