Version 2 2024-03-21, 19:27Version 2 2024-03-21, 19:27
Version 1 2024-02-06, 20:11Version 1 2024-02-06, 20:11
journal contribution
posted on 2024-03-21, 19:27authored byKavanal P. Prasanthkumar, Faseelath Valayankadan, Charuvila T. Aravindakumar, P. Arun, Aswathy Babu, Juan R. Alvarez-Idaboy
Oxidative reactions of the hydroxyl radical (·OH)
with methimazole
(MMI), an antithyroid drug, are crucial for understanding its fate
in oxidizing environments. By synergistically integrating density
functional theory and ultraperformance liquid chromatography–quadrupole
time-of-flight tandem mass spectrometry (UPLC-Q-TOF MS/MS) techniques,
we elucidated the transients and transformation products (TPs) arising
from the ·OH–MMI reactions. We probed two hydrogen-atom
abstraction (HA) reactions, three radical adduct formation reactions,
and single electron transfer (SET) at the M06-2X/6-311++G(d,p)/SMD(water)
level. All proposed reaction channels, except for HA from the methyl
group and SET, were found to be barrier-free. SET is the dominant
oxidation pathway, accounting for 44% of oxidations, as determined
by branching ratio analysis. The selenium analogue, MSeI, exhibited
minor reactivity differences compared to MMI, yet its overall patterns
resembled those of ·OH–MMI reactions. TPs were generated
experimentally by reacting MMI with ·OH produced by UV-photolysis
of H2O2. Eight TPs were identified from an approximately
24% degradation of MMI using UPLC-Q-TOF MS/MS analysis, and an additional
two TPs were identified from the approximately 52% degraded MMI sample.
The exact identities of all of the TPs were established through their
corresponding fragmentation patterns. This study elucidates the drug’s
susceptibility to free radical species under physiologically relevant
conditions.