The Bakkenolides from the Root of Petasites formosanus and Their Cytotoxicity.

Thirty-two new bakkenolides, bakkenolides-Db (1)--Dh (7), -Fa (8), -Fb (9), -I (10)--M (14), -Na (15), -Nb (16), -O (17)--T (22), -Ua (23), -Ub (24), -V (25)--X (27), -Ya (28), -Yb (29), -Za (30), -Zb (31) and -III (32), from the roots of Petasites formosanus together with thirty known compounds were isolated. The structures were characterized by spectral analysis. The locations, C-1 and/or C-9 bakkenolide skeleton, of the substituents, such as acetoxy, isobutyroyloxy and isovaleroyloxy groups, can be determined by the chemical shifts of their signals and the H-1 and/H-9 in the 1H-NMR spectra. The cytotoxicity was also discussed.