Identification of SARS-CoV-2 inhibitors from extracts of Thunb.

Thunb., a perennial herb belonging to the Saururaceae family is a well-known ingredient of Traditional Chinese medicine (TCM) with several therapeutic properties. During the severe acute respiratory syndrome (SARS) outbreak in China, it was one of the approved ingredients in SARS preventative formulations and therefore, the plant may contain novel bioactive chemicals that can be used to suppress the replication of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a virus for which there are currently no effective drugs available. Like all RNA viruses, SARS-CoV-2 encode RNA-dependent RNA polymerase (RdRp) enzyme which aids viral gene transcription and replication. The present study is aimed at understanding the potential of bioactive compounds from as inhibitors of the SARS-CoV-2 RdRp enzyme. We investigated the drug-likeness of the plant's active constituents, such as alkaloids, polyphenols, and flavonoids, as well as their binding affinity for the RdRp enzyme. Molecular docking experiments show that compounds (1,2,3,4,5-pentamethoxy-dibenzo-quinolin-7-one), (7-oxodehydroasimilobine), and (1,2-dimethoxy-3-hydroxy-5-oxonoraporphine) have a high affinity for the drug target and that the complexes are maintained by hydrogen bonds with residues like Arg553, Cys622 and Asp623, as well as hydrophobic interactions with other residues. The lead compounds' complexes with the target enzyme remained stable throughout the molecular dynamics simulation. Analysis of molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) and molecular mechanics generalized Born surface area (MM-GBSA) revealed the key residues contributing considerably to binding free energy. Thus, the findings reveal the potential of bioactive compounds as anti-SARS-CoV-2 drug candidate molecules against the target enzyme.