The antioxidative potential of benzofuran-stilbene hybrid derivatives: a comparison between natural and synthetic compounds

The antioxidative activity of natural product compound amurensin H (1) and its three synthetic compounds 5-(6-hydroxy-2-(4-hydroxyphenyl)benzofuran-3-yl)benzene-1,3-diol (2), (E)-2-(4-hydroxyphenyl)-4-(4-hydroxystyryl)benzofuran-6-ol (3), and (E)-5-(6-hydroxy-4-(4-hydroxystyryl)benzofuran-3-yl)benzene-1,3-diol (4) are extensively studied by DFT (density functional theory) method. At the theoretical B3LYP/6-311G(d,p) level, the HAT (hydrogen atom transfer) mechanism is assignable to compounds 1-4 in gas, but the SPL-ET (sequential proton loss-electron transfer) mechanism is the main way in water and methanol. The antioxidative actions of the studied compounds are mainly based on OH bond breakage, especially OH groups directly substituted at benzofuran nucleus. Amurensin H (1) is better than the remaining compounds due to 6-OH group. 1-6-OH induces the low bond BDE (bond dissociation enthalpy) and PA (proton affinity) values in thermal analysis. Importantly, the kinetic reaction of 1-6-OH + HOO• in methanol exerts the lowest ΔG# value of 5.6 kcal/mol and the highest K value of 1.983 x 1010 L/mol.s. At the B3LYP/6-311G(d,p)/LANL2DZ level, the successful formation of complex [Zn(compound 1)2(H2O)2] at 6-OH is confirmed by molecular orbital and UV-Vis spectroscopic analyses.