Acylated Lignans Isolated from Brachanthemum gobicum and Their Trypanocidal Activity

Eight isovaleryllignans (1–4 and 8–11), three isovalerylphenylpropanoids (5–7), three known lignans (12–14), and four known compounds were isolated from an extract of the aerial part of Brachanthemum gobicum. The structures of the isolated compounds were elucidated based on NMR and MS data analyses. The enantiomers of compounds 1–3, 5, 8, and 9 were isolated using chiral-phase HPLC, and the absolute configurations of 1a/1b–3a/3b, 5a/5b, 8a/8b, and 9a/9b were elucidated from their optical rotations and ECD spectra; the other lignans were assumed to be racemic or scalemic by chiral-phase HPLC analyses and optical rotation data. Some of the acylated lignans (racemic mixtures) (1–4, 8, 9, and 12–14) exhibited moderate inhibitory activities against Trypanosoma congolense, the causative agent of nagana disease in animals.