Bioassay-guided separation of antioxidants in Blaps rynchopetera Fairmaire and their theoretical mechanism

Blaps rynchopetera Fairmaire is a medicinal insect with a wide range of biological activities. Some of its activities, including anti-cancer and anti-inflammatory activities, are closely related to antioxidant capacity. In this study, a method was established to investigate components and theoretical mechanism of antioxidant from B. rynchopetera. As a result, two antioxidants were obtained by bioassay-guided separation and identified as 4-(2-hydroxyethyl)-1,2-benzenediol and 4-ethylbenzol-1,3-diol. Their EC₅₀ were 20.20 ± 0.30 μM and 22.90 ± 1.30 μM for ABTS·⁺ scavenging, and 153.00 ± 2.00 μM and 301.00 ± 3.00 μM for DPPH· scavenging, respectively. The thermodynamic investigation indicated that the 2-OH of 4-(2-hydroxyethyl)-1,2-benzenediol and the 1-OH of 4-ethylbenzol-1,3-diol were more susceptible to be attacked by free radicals. They tended to exert antioxidant effects via the sequential proton loss electron transfer mechanism in polar media, whereas the hydrogen atom transfer mechanism was more likely to occur in non-polar media. In addition, frontier molecular orbital theory and energy barrier analysis suggested that 4-(2-hydroxyethyl)-1,2-benzenediol was more likely to react with DPPH·. These results confirmed that 4-(2-hydroxyethyl)-1,2-benzenediol had better antioxidant potential.