Theoretical Insights into the Effect of Halogenated Substituent on the Electronic Structure and Spectroscopic Properties of the Favipiravir Tautomeric Forms and Its Implications on the Treatment of COVID-19

In this study, we systematically investigated the electronic structure, spectroscopic (nuclear magnetic resonance, infrared, Raman, electron ionization mass spectrometry, UV-Vis, circular dichroism, and emission) properties, and tautomerism of halogenated favipiravir compounds (fluorine, chlorine, and bromine) from a computational perspective. Additionally, the effects of hydration on the proton transfer mechanism of the tautomeric forms of the halogenated favipiravir compounds are discussed. Our results suggest that spectroscopic properties allow for the elucidation of such tautomeric forms. As is well-known, the favipiravir compound has excellent antiviral properties and hence was recently tested for the treatment of new coronavirus (SARS-CoV-2). Through in silico modeling, in the current study, we evaluate the role of such tautomeric forms in order to consider the effect of drug-metabolism into the inhibition process of the main protease (M^pro) and RNA-dependent RNA polymerase (RdRp) of SARS-CoV-2 virus. These findings clearly indicated that all title compounds are better as RNA-inhibiting.