Leaves of Magnolia liliflora Desr. as a high-potential by-product: Lignans composition, antioxidant, anti-inflammatory, anti-phytopathogenic fungal and phytotoxic activities

After harvesting the flower buds of Magnolia liliflora Desr. (the traditional Chinese medicine known as "Xinyi"), a significant quantity of M. liliflora leaf (MLL) was generated as a by-product. The aim of this study is to verify the potential use of MLL and isolate its bioactive compounds with antioxidant, anti-inflammatory, antifungal and phytotoxic activities. The ethyl acetate extract (ETE) from ethanol extract of MLL with the highest lignan content and antioxidant activity showed a good application value, from which four new lignans (1–4) along with fifteen known lignans (5–19) were isolated. The structures of lignans were established on the basis of 1D and 2D NMR data and HRESIMS data interpretation. Compounds 2, 9 and 10 exhibited antioxidant activities as assessed by DPPH, ABTS and FRAP methods. Compounds 2–3, 9–11 and 13–14 showed pronounced anti-inflammatory activities compared with positive control indomethacin. Compounds 9, 11 and 19 showed antifungal effects on three plant pathogens of economic importance in agriculture (Fusarium graminearum, Pyricularia oryzae, Alternaria alternata) with MIC values ranging from 32 to 128 μg/mL. Compounds 5 and 11 showed an inhibitory effect on lettuce shoots with EC50 = 0.37 and 0.95 mM, respectively. The results indicated that MLL could be regarded as a promising high-potential by-product and inexpensive source of lignans for the pharmaceutical, food and agricultural industries.