Phenolic compounds from the fungus Inonotus obliquus and their antioxidant properties

The medicinal fungus Inonotus obliquus (Pers.: Fr.) Pilat (family Hymenochaetaceae) is widely distributed in Europe, Asia and North America. 1 This mushroom, which lives on tree trunks of Betula (birch) but rarely on Ulmus, Alnus and Fraxinus, has been used as a folk medicine for treating cancer in Russia and western Siberia, and has also been used to prevent and treat heart, liver and stomach diseases and tuberculosis. 2,3Chemical investigations show that I. obliquus produces a diverse range of secondary metabolites, including phenolic compounds, 4 melanins 5 and lanostane-type triterpenoids. 6Among these are active components with antioxidant, 4 antitumor 7 and antiviral activities, 8 as well as compounds that improve human immunity against pathogenic microbial infections.Reactive oxygen species are major primary catalysts for initiating oxidation in vivo and in vitro.0][11] Accumulating excess reactive oxygen species damages lipids, proteins, carbohydrates and DNA, leading to oxidative stress, loss of cell function and apoptosis or necrosis. 12,13All of these biochemical processes are common in various diseases, such as cancers, inflammation, atherosclerosis and cardiovascular disease. 14Therefore, exploring the functions of antioxidants that scavenge reactive oxygen species may be of great value to prevent the onset and propagation of oxidative stress.As part of our search for free radical scavengers from medicinal fungi, two new phenolic antioxidants 1 and 2 were isolated with known compounds 4-(3,4-dihydroxyphenyl)but-3-en-2-one (3), 4-hydroxy-3,5-dimethoxybenzoic acid (4), 3,4-dihydroxybenzaldehyde (5), 4-hydroxybenzene-1,3-dioic acid (6) and 3,4-dihydroxybenzoic acid (7) from a methanol extract of the I. obliquus fruiting body (Figure 1).In this study, we describe the isolation and structural determination of the phenolic antioxidants from the I. obliquus fruiting body as well as their antioxidant properties.The I. obliquus fruiting bodies were purchased at an herbal drug market in Keumsan, Chungnam Province, Korea.The ground fruiting bodies (5 kg) were extracted twice with 70% aqueous methanol at 60 °C for 12 h.After removing the methanol under reduced pressure, the aqueous solution was partitioned between hexane, chloroform,