The rates of 1,1-diphenyl-2-picryhydrazyl (DPPH)-free radical scavenging and hydroxyl radical eliminating were employed as indexes to qualitatively and quantitatively analyse the radical scavenging activity of the extracts with different solvents from fermented mycelia of Hirsutella huangshanensis RCEF0868, the anamorph of Ophiocordyceps formosana (FMOF). The results showed that both the aqueous extract and the methanol extract had significant radical scavenging activity. The half maximal inhibitory concentrations (IC50) of the aqueous extract on DPPH-free radical and hydroxyl radical are 0.85 and 1.37 mg/mL, respectively, while the IC50 of methanol extract is 1.23 and 2.91 mg/mL, respectively. The combined liquid chromatography-diode array detector-high resolution mass spectrometer(HRMS) analysis and activity determination revealed that the molecular formulas of three radical scavengers in aqueous extract were C6H14O6(1), C14H17N5O8(2) and C20H33N5O9(3). In addition to the compound 1, the methanol extract had another three radical scavengers as C30H22O11(4), C30H22O10(5) and C30H18O10(6). All the six kinds of components exhibited the DPPH radical scavenging activity, and compounds 1, 4 and 5 also showed the hydroxyl radical eliminating activity at the same time. By querying the database of natural products and reference to the relevant reports, compound 3 may be a new entity. The others were respectively cordycepic acid, succinoadenosine, 4α-oxyrugulosin, rugulosin and skyrin and, among them, succinoadenosine and 4α-oxyrugulosin were found in entomogenous fungi for the first time.
Keywords: DPPH-free radical; Hirsutella huangshanensis; LC–MS; activity determination; hydroxyl radical.