Exploring the Pyrimidine Scaffold for the Development of SARS-CoV-2 Mpro Inhibitors.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is still a major public health issue, even today. Among the SARS-CoV-2 nonstructural proteins, the main protease (Mpro) plays a critical role in viral polyprotein processing and is therefore indispensable for viral replication. For this reason, it represents one of the most promising therapeutic targets for the development of antiviral agents against SARS-CoV-2. Currently, only one protease antiviral agent (nirmatrelvir) has received emergency approval for COVID-19 treatment, the disease caused by SARS-CoV-2 infection. However, the emergence of viral mutations may compromise its efficacy, highlighting the urgent need to develop new, safe, and effective protease antiviral agents. In the present work, we designed and synthesized new SARS-CoV-2 Mpro small-molecule inhibitors endowed with a pyrimidine scaffold. A series of derivatives were evaluated in both biochemical and cell-based assays to assess their antiviral efficacy, with some of them being able to inhibit the SARS-CoV-2 Mpro activity and to suppress viral replication. Docking studies were confirmed by site-directed mutagenesis, and the mechanism of action of the most promising compound was elucidated.