Antifungal Sesquiterpenoids from Michelia formosana Leaf Essential Oil against Wood-Rotting Fungi

Michelia formosana (Kanehira) Masamune is a broad-leaved species widespread in East Asia; the wood extract and its constituents possess antifungal activity against wood-decay fungi. Antifungal activities of leaf essential oil and its constituents from M. formosana were investigated in the present study. Bioassay-guided isolation was applied to isolate the phytochemicals from leaf essential oil. 1D and 2D NMR, FTIR, and MS spectroscopic analyses were applied to elucidate the chemical structures of isolated compounds. Leaf essential oil displayed antifungal activity against wood decay fungi and was further separated into 11 fractions by column chromatography. Four sesquiterpenoids were isolated and identified from the active fractions of leaf essential oil through bioassay-guided isolation. Among these sesquiterpenoids, guaiol, bulnesol, and beta-elemol have higher antifungal activity against brown-rot fungus Laetiporus sulphureus and white-rot fungus Lenzites betulina. Leaf essential oil and active compounds showed better antifungal activity against L. sulphureus than against L. betulina. The molecular structure of active sesquiterpenoids all contain the hydroxyisopropyl group. Antifungal sesquiterpenoids from M. formosana leaf essential oil show potential as natural fungicides for decay control of lignocellulosic materials.