Pityriacitrin B for COVID-19

Coronaviruses (CoVs) have recently emerged as significant causes of respiratory disease outbreaks. The novel coronavirus pneumonia of 2019, known as COVID-19, are highly infectious and triggered by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Understanding virus-host interactions and molecular targets in host cell death signalling is crucial for treatment development. Small natural compounds like celastrol and curcumin, acting as proteasome inhibitors, can potentially modify NF-κB signalling for treating SARS-CoV-2 infections. Various natural constituents, including alkaloids, flavonoids, terpenoids, diarylheptanoids, and anthraquinones, inhibit viral infection, progression, and amplification of coronaviruses. Derived from medicinal herbs, these compounds possess anti-inflammatory and antiviral properties, impacting the viral life cycle, including entry, replication, assembly, and release of COVID-19 virions. This review focuses on the development of small molecules of non-covalent inhibitors targeting the Main Protease (Mpro, also called 3CLpro) enzyme of SARS-CoV-2. It highlights the design using molecular dynamics (MD) studies and computational methods for further improvements in Mpro inhibitor design. The in-silico approach, which is pivotal in this process, provides an accelerated virtual avenue for exploring and developing potential inhibitors, representing the latest advancements in drug design.

The main protease (Mpro) of the newly emerged severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was subjected to hyphenated pharmacophoric-based and structural-based virtual screenings using a library of microbial natural products (>24,000 compounds). Subsequent filtering of the resulted hits according to the Lipinski’s rules was applied to select only the drug-like molecules. Top-scoring hits were further filtered out depending on their ability to show constant good binding affinities towards the molecular dynamic simulation (MDS)-derived enzyme’s conformers. Final MDS experiments were performed on the ligand–protein complexes (compounds 1–12, Table S1) to verify their binding modes and calculate their binding free energy. Consequently, a final selection of six compounds (1–6) was proposed to possess high potential as anti-SARS-CoV-2 drug candidates. Our study provides insight into the role of the Mpro structural flexibility during interactions with the possible inhibitors and sheds light on the structure-based design of anti-coronavirus disease 2019 (COVID-19) therapeutics targeting SARS-CoV-2.