Synthesis and Biological Evaluation of Benzothiazolyl-pyridine Hybrids as New Antiviral Agents against H5N1 Bird Flu and SARS-COV-2 Viruses.

A novel series of benzothiazolyl-pyridine hybrids 8a - h and 14a - e were produced from the reaction of enamine derivative 4 with each of the arylcyanoacetamides 5a - h and cyanoacetohydrazides 9a - e . The new products were characterized by spectral techniques (IR, 1 H NMR, 13 C NMR, and MS). Biological evaluation of 8a - h and 14a - e in vitro against H5N1 and SARS-COV-2 viruses showed that several compounds had significant activity. Compounds 8f - h , which contain fluorine atoms, have better activity against H5N1 and anti-SARS-CoV-2 viruses than the other compounds included in this study. Compound 8h has a trifluoromethyl group at position-3 of the phenyl ring and exhibits a high activity against H5N1 virus with 93 and 60% inhibition at concentrations of 0.5 and 0.25 μmol/μL, respectively, among the tested compounds, and it also showed anti-SARS-CoV-2 virus with a half-maximum inhibition rate of 3.669 μM, among the remaining compounds. The mechanism of action of 8f - h , which is expected to be repurposed against COVID-19, was investigated. The results showed that the compounds have virucidal effects at different stages of the three mechanisms of action. Furthermore, compounds 8f - h were found to possess CoV-3CL protease inhibitory activities with IC 50 values of 544.6, 868.2, and 240.6 μg/mL, respectively, compared to IC 50 = 129.8 μg/mL of the standard drug lopinavir. Interestingly, compounds 8f - h also showed high inhibitory activity against the H5N1 virus as well as the SARS-CoV-2 virus. Moreover, compounds 8f - h fit admirably into the active site of the SARS-CoV-2 main protease (PDB ID: 6LU7) using the molecular docking Moe software 2015.10.