Comprehensive Virtual Screening of the Antiviral Potentialities of Marine Polycyclic Guanidine Alkaloids against SARS-CoV-2 (Covid-19)

A comprehensive in silico binding affinity of fifteen guanidine alkaloids against five different proteins of SARS-CoV-2 has been investigated. The investigated proteins are COVID-19 main protease (M^pro) (PDB ID: 6lu7), spike glycoprotein (PDB ID: 6VYB), nucleocapsid phosphoprotein (PDB ID: 6VYO), membrane glycoprotein (PDB ID: 6M17), and non-structural protein (nsp10) (PDB ID: 6W4H). The binding energies for all tested compounds indicated promising binding affinities. A noticeable superiority for the pentacyclic alkaloids particularly, crambescidin 786 (5) and crambescidin 826 (13) have been observed. Compound 5 exhibited very good binding affinities against M^pro (ΔG = -8.05 kcal/mol), nucleocapsid phosphoprotein (ΔG = -6.49 kcal/mol), and nsp10 (ΔG = -9.06 kcal/mol). Compound 13 showed promising binding affinities against M^pro (ΔG = -7.99 kcal/mol), spike glycoproteins (ΔG = -6.95 kcal/mol), and nucleocapsid phosphoprotein (ΔG = -8.01 kcal/mol). Such promising activities might be attributed to the long ω-fatty acid chain, which may play a vital role in binding within the active sites. The ADMET studies were carried out in silico for the 15 compounds, all examined compounds (except compounds 8 and 15) have low or very low BBB penetration levels. Compounds 1, 5, 6, 9, 12 and 13 showed optimal range levels of ADMET aqueous solubility. Compounds 1, 2, 3, 8, and 15 were predicted to have good intestinal absorption levels, while compounds 4, 7, 9, 10, and 14 showed moderate absorption levels. All examined alkaloids (except the bicyclic compound 8) were predicted not to be inhibitors of CYP2D6, non-hepatotoxic, and bind plasma protein with a percentage less than 90%. The toxicity of the tested compounds was screened in silico against five models (FDA rodent carcinogenicity, carcinogenic potency TD₅₀, rat maximum tolerated dose, rat oral LD₅₀ and rat chronic LOAEL). All compounds showed expected low toxicity against the tested models.