Tautomerism‐Governed Two‐Proton‐Coupled Electron Transfer in the Oxidation of a Molnupiravir by Electrogenerated Superoxide Radical Anion in N , N ‐Dimethylformamide

ABSTRACT Molnupiravir is a nucleoside analog antiviral whose activity originates from the tautomeric flexibility of its N 4 ‐hydroxycytosine moiety, yet its redox reactivity toward reactive oxygen species (ROS) has not been elucidated at the molecular level. In this study, we investigate the interaction between molnupiravir and electrogenerated superoxide radical anion (O 2 •− ) in aprotic N , N‐ dimethylformamide using cyclic voltammetry (CV) with density functional theory (DFT) calculations. Electrochemical measurements reveal loss of reversibility of the O 2 /O 2 •− redox couple in the presence of molnupiravir and the emergence of a reversible redox couple at more negative potentials. Comparative analyses with N 4 ‐hydroxycytosine, cytosine, and uracil demonstrate that this behavior is unique to the N 4 ‐hydroxycytosine moiety. Thermodynamic and reaction coordinate analyses based on DFT show that the oxidation of molnupiravir by O 2 •− proceeds via a concerted two‐proton‐coupled electron transfer (2PCET) mechanism rather than stepwise transfer. The oxime tautomer forms a hydrogen‐bonded prereactive complex with O 2 •− , enabling the simultaneous transfer of two protons and one electron in a single kinetic event. No persistent radical intermediates were detected by in situ electrolytic ESR spectroscopy, consistent with rapid tautomerization following PCET. These findings highlight how tautomerism governs PCET‐driven redox reactivity in nucleobase‐modified drugs, providing a framework linking electrochemistry and antiviral molecular design.