Norsesquiterpene derivatives from the roots of Ligularia fischeri.

Four new norsesquiterpene derivatives with various rare skeletons: 1 beta-hydroxy-6 alpha-isobutyryloxy-9-noreremophil-7(11),8(10)-dien-8(12)-olide ( 1), 1 beta-acetoxy-6 alpha-isobutyryloxy-9-noreremophil-7(11),8(10)-dien-8(12)-olide ( 2), ligularate ( 3) and 9-oxoplatyphyllide ( 4), as well as four known sesquiterpenes, platyphyllide ( 5), 1-hydroxyplatyphyllide ( 6), 1 alpha-chloro-6 beta-isobutyryloxy-9-oxo-10 beta-hydroxyfuranoeremophilane ( 7), and 1 alpha-chloro-6 beta-angeloyloxy-9-oxo-10 beta-hydroxyfuranoeremophilane ( 8), have been isolated from an extract of the dried roots of Ligularia fischeri (Compositae). The structures of the new compounds were established by spectroscopic methods including extensive 2D NMR techniques ( (1)H- (1)H COSY, HMQC, HMBC and (1)H- (1)H NOESY) and HR-ESI-MS. In addition, a plausible biosyntheticpathway for compounds 1, 2 and 3 is described.