Prenylated indole alkaloids and lignans from the flower buds of Tussilago farfara

Six new compounds including four prenylated indole alkaloids (1–4) and two lignans (5–6), along with eight known cometabolites (7–14), were isolated from the flower buds of Tussilago farfara. Structures of the new compounds were elucidated by comparison with structurally related known analogues and also by comprehensive spectroscopic analyses. Their absolute configurations were determined by a variety of means including Mosher's method, Marfey's analysis, electronic circular dichroism (ECD) exciton chirality method and ECD calculations. Our bioassays have established that compounds 1 and 2 showed potent α-glucosidase inhibitory activity with IC50 values of 105 ± 4.7 and 35.2 ± 3.2 μM, respectively, while the known 13 and 14 exerted moderate DPPH radical scavenging activity with IC50 values of 45.2 ± 2.9 and 29.2 ± 2.0 μM, respectively.