Chemical constituents from Limonium tubiflorum and their in silico evaluation as potential antiviral agents against SARS-CoV-2

Wild plants growing in the Egyptian deserts are facing abiotic stress, which can lead to interesting & safe natural products possessing potential chemical profiles. Consequently, our study was designed to assess the phytochemical composition of the aerial parts of Limonium tubiflorum (family Plumbaginaceae) growing wild in Egypt for the first time. In addition, in silico screening and molecular dynamic simulation of all isolated phytoconstituents were run against the main protease (M-pro) and spike glycoprotein SARS-CoV-2 targets which displayed a crucial role in the replication of this virus. Our findings showed that the phytochemical investigation of 70% ethanol extract of L. tubiflorum aerial parts afforded six known flavonoids; myricetin 3-O-(2 ''-galloyl)-beta-D-galactopyranoside (1), myricetin 3-O-(2 ''-galloyl)-alpha-L-rhamnopyranoside (2), myricetin 3-O-(3 ''-galloyl)-alpha-L-rhamnopyranoside (3), myricetin 3-O-beta-D-galactopyranoside (5), apigenin (6), myricetin (7), along with two known phenolic acid derivatives; gallic acid (4) and ethyl gallate (8). Docking studies revealed that compounds (1) & (2) were the most effective compounds with binding energies of -17.9664 & -18.6652 kcal mol(-1) against main protease and -18.9244 & -18.9272 kcal mol(-1) towards spike glycoprotein receptors, respectively. The molecular dynamics simulation experiment agreed with the docking study and reported stability of compounds (1) and (2) against the selected targets which was proved by low RMSD for the tested components. Moreover, the structure-activity relationship revealed that the presence of the galloyl moiety is necessary for enhancement of the activity. Overall, the galloyl substructure of myricetin 3-O-glycoside derivatives (1 and 2) isolated from L. tubiflorum may be a possible lead for developing COVID-19 drugs. Further, in vitro and in vivo assays are recommended to support our in silico studies.