Antiplasmodial activity of aporphine alkaloids and sesquiterpene lactones from Liriodendron tulipifera L.

Aim of the study: The objective of this study was to isolate and characterize the active constituents of the traditionally used antimalarial plant Liriodendron tulipifera by antiplasmodial-assay guided fractionation. Materials and methods: Bark and leaves were extracted with solvents of increasing polarity. Fractions were generated using flash chromatography, counter current chromatography and preparative HPLC and subjected to in vitro antiplasmodial and cytotoxicity assays. Active fractions were subjected to further fractionation until pure compounds were isolated, for which the IC ₅₀ values were calculated. Results and discussion: Six known aporphine alkaloids, asimilobine (1), norushinsunine (2), norglaucine (3), liriodenine (4), anonaine (5) and oxoglaucine (6) were found to be responsible for the antiplasmodial activity of the bark. Leaves yielded two known sesquiterpene lactones, peroxyferolide (7) and lipiferolide (8) with antiplasmodial activity. The antiplasmodial activity of (2) (IC₅₀ = 29.6 μg/mL), (3) (IC₅₀ = 22.0 μg/mL), (6) (IC₅₀ = 9.1 μg/mL), (7) (IC₅₀ = 6.2 μg/mL) and (8) (IC₅₀ = 1.8 μg/mL) are reported for the first time. Conclusion: This work supports the historical use of Liriodendron tulipifera as an antimalarial remedy of the United States and characterizes its antiplasmodial constituents.