Eremophilenolides from Ligularia fischeri

Chemical Constituents of Ligularia Species (Asteraceae) and Their Diversity in East Asia

More than 100 Ligularia species and those of several related genera (Cremanthodium, Cacalia, Senecio, and others) in the plant family Senecioneae grow in East Asia. For many years, researchers have studied the chemical constituents of these plants, and terpenoids, flavonoids, sterols, alkaloids, and aromatic compounds have been isolated. Among these, in particular, numerous sesquiterpenoids were reported. In this contribution, relevant chemical studies are described mainly from literature reports appearing since 2000, inclusive of investigations performed by the present authors, on the diversity in secondary metabolites of Ligularia growing in the Hengduan Mountains area of China, focusing on eremophilane sesquiterpenoids and other metabolites. Terpenoids and aromatic compounds (totaling 1049), both new and known, are listed. Genetic studies and synthesis investigations are also reviewed briefly.

Eremophilane-type Sesquiterpenes from the Leaves of Ligularia Virgaurea

A phytochemical study of the ethanolic extract of the leaves of Ligularia virgaurea led to the isolation of a new eremophilane-type sesquiterpene lactone, (4 S,5 R,6 S,8 S,10 R)–6β-angeloyloxy-eremophil-7(11)-en-10βH-8α,12-olide (1), along with a known eremophilane-type sesquiterpene, (4 S,5 R,6 S,10 S)–6β-angeloyloxy-10βH-furanoeremophil-9-one (2). Their structures were elucidated by extensive spectroscopic methods, including 1D and 2D nuclear magnetic resonance and high-resolution electrospray ionization mass spectrometry experiments, and the absolute configurations were confirmed by single-crystal X-ray diffraction analysis using the anomalous scattering of Cu Kα radiation.

Chemical Lineages of Ligularia Fischeri

Six Ligularia fischeri samples, two from Sichuan (samples 1 and 2) and four from Chongqing (samples 3–6), were examined for root chemicals and the DNA sequence of the internal transcribed spacers of the ribosomal RNA gene. Samples 2 and 3 contained benzofurans. The isolation of benzofurans shows that the chemical diversity in L. fischeri is higher than previously reported. Samples 1, 4, 5, and 6 contained eremophilanes. However, the compounds were different between sample 1 and samples 4–6, indicating variation within eremophilane producers. DNA data indicated that introgression could be a mechanism of benzofuran production in sample 2 and that sample 1 and samples 4–6 were genetically separate.

Chemical and genetic similarity and diversity of Ligularia anoleuca and L. fischeri collected in the Hengduan Mountains of China

The sesquiterpenoid composition in the root and the DNA sequences of evolutionarily neutral regions were studied in Ligularia anoleuca and Ligularia fischeri (Asteraceae) collected in the Sichuan Province of China. LC-MS analysis showed that L. anoleuca populations from different localities had different chemical compositions. However, the isolated compounds were similar to each other, indicating that the differences in chemical composition were not large. The DNA analysis suggested that the two species were indistinguishable. Seventeen furanoeremophilanes and an eremophilane acetal were isolated.

6β-Hy-droxy-eremophil-7(11)-en-8β,12-olide

The title eremophilenolide, C(15)H(22)O(3), is a natural compound isolated from Senecio laetus Edgew. The two cis-fused six-membered rings have chair confomations and the five-membered ring has a planar envelope conformation [maximum deviation = 0.010 (1) Å]. The β-hy-droxy group participates in inter-molecular O-H⋯O hydrogen bonding, forming mol-ecular chains along the a axis.

A New Norsesquiterpenoid from the Roots of Ligularia Fischeri

A new norsesquiterpenoid, (4aS,5S)-5,6,7,8-tetrahydro-3-hydroxy-4a,5-dimethylnaphthalen-2(4aH)-one, along with three known compounds were isolated from the roots of Ligularia fischeri. Their structures were identified by IR, EI-MS, HR-ESI-MS, 1D NMR and 2D NMR.

A pair of epimeric spirosesquiterpenes from the roots of Ligularia fischeri

Two new highly oxygenated spirosesquiterpene lactones, ligulactones A (1) and B (2), and one known sesquiterpenoid, 1beta,10beta-epoxy-6beta-isobutyryloxy-9-oxo-furanoeremophilane (3), were isolated from the roots of Ligularia fischeri. Their structures and relative configurations were elucidated by 1D and 2D NMR and MS data and by comparison of their NMR data with those of related compounds. Single-crystal X-ray diffraction analyses confirmed their structures. Compounds 1 and 2 are C-7 epimers. A possible biosynthetic process for their formation is proposed. Structure 3 was proposed as the likely parent compound for the two new epimeric sesquiterpenoids.

Four new terpenoids from the roots of Ligularia narynensis

Four new oplopane and guaiane type sesquiterpenoids (1-3), and a monoterpenoid (4) together with three known monoterpenoids (5-7), have been isolated from the roots of Ligularia narynensis. The structures of 1-4 were elucidated as 3beta,4-diacetoxy-8alpha-(2-methylbutyryloxy)-9alpha-(4-methylsenecioyloxy)-11alpha,12-epoxyoplop-10 (14)-ene (1), 3beta,4-diacetoxy-9alpha-(4-acetoxy-4-methylsenecioyloxy)-2beta,8alpha-di (2-methylbutyryloxy)-11alpha,12-epoxyoplop-10 (14)-ene (2), 2alpha-hydroxy-1betaH,7alphaH,10alphaH-guai-4,11 (12)-dien-3-one (3) and 1alpha,2beta,3alpha,6alpha-tetrahydroxy-p-menthane (4) by spectroscopic methods. 1 and 2 were evaluated for their in vitro cytotoxic activity against cultured SMMC-7721 (human hepatoma), L02 (human hepatocyte), and HL-60 (human promyelocytic leukaemia) cell lines.