Novel Fluorescent Benzothiazolyl-Coumarin Hybrids as Anti-SARS-COVID-2 Agents Supported by Molecular Docking Studies: Design, Synthesis, X-ray Crystal Structures, DFT, and TD-DFT/PCM Calculations.

This study revealed the design and preparation of new 3-(benzo[ d ]thiazol-2-yl)-2 H -chromen-2-one derivatives 9a-h . The structures of the synthesized products were elucidated by their spectroscopic data and X-ray crystallography for compounds 9a and 9d . The prepared new compounds were measured for their fluorescence, and a good result indicated that the emission efficiency was decreased by increasing the electron-withdrawing groups from the unsubstituted compound 9a to the highly substituted derivative 9h (2 Br heavy atoms). On the other hand, the B3LYP/6-311G** theoretical level of theory was used to optimize the quantum mechanical calculations of the geometrical characteristics and energy of the novel compounds 9a-h under study. The electronic transition was investigated using the TD-DFT/PCM B3LYP approach, which uses time-dependent density functional calculations. Moreover, the compounds exhibited nonlinear optical properties (NLO) and a small HOMO-LUMO energy gap, which makes them easy to polarize. Furthermore, the acquired infrared spectra were compared with the expected harmonic vibrations of the substances 9a-h . On the other hand, binding energy analyses of compounds 9a-h with human corona virus nucleocapsid protein Nl63 (PDB ID: 5epw) were predicted using molecular docking and virtual screening tools. The results showed a promising binding and how these potent compounds were inhibiting the COVID-19 virus. Compound 9h was the most active anti-COVID-19 agent among all the synthesized benzothiazolyl-coumarin derivatives, as it forms five bonds. The presence of the two bromine atoms in its structure was responsible for the potent activity.