In-Silico approach for identification of effective and stable inhibitors for COVID-19 main protease (Mpro) from flavonoid based phytochemical constituents ofCalendula officinalis

The recent outbreak of the coronavirus disease COVID-19 is putting the world towards a great threat. A recent study revealed COVID-19 main protease (M-pro) is responsible for the proteolytic mutation of this virus and is essential for its life cycle. Thus inhibition of this protease will eventually lead to the destruction of this virus. In-Silico Molecular docking was performed with the Native ligand and the 15 flavonoid based phytochemicals ofCalendula officinalsto check their binding affinity towards the COVID-19 main protease. Finally, the top 3 compounds with the highest affinity have been chosen for molecular dynamics simulation to analyses their dynamic properties and conformational flexibility or stability. In-Silico Docking showed that major phytochemicals ofCalendula officinalsi.e. rutin, isorhamnetin-3-O-beta-D, calendoflaside, narcissin, calendulaglycoside B, calenduloside, calendoflavoside have better binding energy than the native ligand (inhibitor N3). MD simulation of 100 ns revealed that all the protease-ligand docked complexes are overall stable as compare to M-pro-native ligand (inhibitor N3) complex. Overall, rutin and caledoflaside showed better stability, compactness, and flexibility. Our in silico(Virtual molecular docking and Molecular dynamics simulation) studies pointed out that flavonoid based phytochemicals of calendula (rutin, isorhamnetin-3-O-beta-D, calendoflaside) may be highly effective for inhibiting M(pro)which is the main protease for SARS-CoV-2 causing the deadly disease COVID-19. Rutin is already used as a drug and the other two compounds can be made available for future use. Thus the study points a way to combat COVID-19 by the use of major flavonoid based phytochemicals ofCalendula officinals. Communicated by Ramaswamy H. Sarma