Objective  To study antioxidant activity of azaphilone compound Penicilone B in vitro and analyze its antioxidant mechanism using Density Functional Theory (DFT).

  Methods  Three in vitro antioxidant methods including ABTS2, 2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) radical scavenging ability, DPPH (2, 2-diphenyl-1-picrylhydrazyl) radical scavenging ability and oxygen radical absorbance capacity (ORAC) assays were used to determine the antioxidant activity of an azaphilone compound Penicilone B firstly. Moreover, DFT was used to optimize molecular structure of Penicilone B and to analyze the antioxidant mechanism from the aspects of the molecular structure parameters, bond dissociation enthalpy (BDE) of the phenolic hydroxyl group, ionization potential (IP) and frontier molecular orbital (FMO) at the level of M06-2x/6-31+G**.

  Results  Penicilone B showed certain antioxidant activity in vitro. The scavenging rates of Penicilone B on ABTS radicals and DPPH radicals were (11.62±1.19)% and (22.68±2.81)% at 100 μg/mL, respectively, while the scavenging rates of positive control vitamin C (Vc) were (43.17±3.88)% and (58.73±4.70)%, respectively. In addition, the ORAC values of Penicilone B and Vc were (1.06±0.06) and (2.87±0.15) μmol trolox/mg, respectively. The DFT calculation results found that phenolic hydroxyl group at C15 position was easy to occur hydrogen-abstraction reaction. Besides, Penicilone B may also terminate the chain reaction of oxidation by directly binding to active free radicals and ring A and ring B were the primary active sites.

  Conclusion  The antioxidant mechanism of azaphilone compounds is investigated by DFT method for the first time in this study. The theoretical calculation result is in agreement with the experiment in vitro, which provides a theoretical basis for the development of azaphilones.