Identification of phytochemicals that inhibit the enzymatic activity of SARS-CoV-2 3-chymotrypsin like protease (3CLpro) in vitro.

SARS-CoV-2, which emerged in Wuhan, China in December of 2019, is classified as a global pandemic. Several studies suggest that phytochemicals exhibit potent anti-viral effects and in this study, we have investigated the use of phytochemicals as potential anti-SARS-CoV-2 agents. Previous studies indicated the importance of viral proteases in the replication of SARS-CoV-2. Among these proteases, papain-like protease and 3-chymotrypsin-like protease are involved in the synthesis of non-structural proteins responsible for the assembly of the replication-transcription complex. Phytochemicals such as rutin, myricetin, and kaempferol, were reported as potential inhibitors of 3CLpro activity in silico. However, recently we have established that there is no correlation between in silico and experimental studies. We have performed in vitro 3CLpro enzymatic assay to screen the potential enzymatic inhibitory effects of 58 phytochemicals selected based on previous literature. Out of the 58 compounds tested, we observed more than 70% inhibitory activity of 3CLpro enzyme by theaflavin, myricetin, betulinic acid at 100µM concentration; and rhein, epigallocatechin gallate, and mangiferin at 200µM concentration. The IC50 values were as follows: theaflavin (79.07µM), myricetin (120.3µM), betulinic acid (71.20µM), epigallocatechin gallate (97.30µM), and mangiferin (100.9µM). In summary, our data indicates that selected phytochemicals exhibited anti-SARS-CoV-2 effects by targeting 3CLpro enzymatic activity