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Quantum chemical calculations at the B3LYP/6–31G* level of theory were employed for the structure-activity relationship and prediction of the antioxidant activity of edaravone and structurally related derivatives using energy (E), ionization potential (IP), bond dissociation energy (BDE), and stabilization energies (ΔEiso). Spin density calculations were also performed for the proposed antioxidant activity mechanism. The electron abstraction is related to electron-donating groups (EDG) at position 3, decreasing the IP when compared to substitution at position 4. The hydrogen abstraction is related to electron-withdrawing groups (EDG) at position 4, decreasing the BDECH when compared to other substitutions, resulting in a better antioxidant activity. The unpaired electron formed by the hydrogen abstraction from the C–H group of the pyrazole ring is localized at 2, 4, and 6 positions. The highest scavenging activity prediction is related to the lowest contribution at the carbon atom. The likely mechanism is related to hydrogen transfer. It was found that antioxidant activity depends on the presence of EDG at the C2 and C4 positions and there is a correlation between IP and BDE. Our results identified three different classes of new derivatives more potent than edaravone.

Quantum chemistry calculations at the B3LYP theory level, together with the 6-31G * basis set were employed to obtain energy (E), ionization potential (IP), bond dissociation energies (BDE), and spindensity distribution for aminophenol derivatives. Calculations of spin densities were performed for radical formed by hydrogen abstraction from the phenolic hydroxyl group. The IP and BDE values are related with more reactive and minus stable compounds. These values and also highest spin densities distribution on the phenolic oxygen shown that 4-regioisomer is more reactive and minus stable compounds, while 3-regioisomer is less reactive and more stable compounds.

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