BACKGROUND The fruit body of medicinal fungus, Sanghuang (Inonotus baumii), is a source of diverse metabolites with health-promoting efficacy through varying mechanisms. The low efficiency of fruit body production and failure to discover valuable metabolites have severely limited more extensive applications. RESULTS A novel compound was discovered and identified as (6,6 '-bis((E)-3,4-dihydroxystyryl)-4,4 '-dihydroxy-2H,2 ' H-[3,3 '-bipyran]-2,2 '-dione (named as Phelligridin LA, PLA). The compound exhibited antioxidant activity against free radicals (DPPH center dot, center dot OH, center dot O-2, and ABTS center dot(+)). The IC50 values of PLA and vitamin C were determined as 18.62 and 11.26 mu mol L-1 (DPPH center dot), 222.56 and 718.48 mu mol L-1 (center dot OH), 611.41 and 340.11 mu mol L-1 (center dot O-2), 73.33 and 44.31 mu mol L-1 (ABTS center dot(+)), which demonstrated that PLA was an efficient scavenger of center dot OH radical. CONCLUSION PLA is a novel antioxidant metabolite purified from the fermentation broth of Sanghuang, which proved that the biomass produced with fermentation was a good source for metabolite isolation. A feasible process was established to obtain this valuable ingredient from the medicinal fungus. This report exemplifies the exploitation of Sanghuang in the context of modern natural product discovery. (c) 2020 Society of Chemical Industry