Chemical and Genetic Study of Ligularia cyathiceps in Yunnan Province of China

Cumulative Data of 1H and 13C NMR Signals and Specific Rotations of Eremophilane Sesquiterpenoids. 1. Bicyclic Eremophilanes (1)

1H and 13C Nuclear Magnetic Resonance (NMR) signals and specific rotations of eremophilane sesquiterpenoids are cumulated as a series of review articles. In the first chapter of this review, 332 bicyclic eremophilanes, namely with no furan or lactone rings (except for epoxides), without 3-OR functionality (except for hydroxy, acetoxy, and carbonyl) are listed in tables. These data may help chemists working in the area of natural products chemistry as well as synthetic scientists.

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.

Germacrene A-A Central Intermediate in Sesquiterpene Biosynthesis

This review summarises known sesquiterpenes whose biosyntheses proceed through the intermediate germacrene A. First, the occurrence and biosynthesis of germacrene A in Nature and its peculiar chemistry will be highlighted, followed by a discussion of 6-6 and 5-7 bicyclic compounds and their more complex derivatives. For each compound the absolute configuration, if it is known, and the reasoning for its assignment is presented.

Chemical and Genetic Identity of Ligularia tsangchanensis and L. muliensis. Isolation of a Cacalol Precursor from a Hybrid of L. tsangchanensis and L. vellerea

The chemical composition and the DNA sequence of an evolutionarily neutral region were studied for three samples of L. tsangchanensis, three samples of L. muliensis, and one sample of a hybrid between L. tsangchanensis and L. vellerea. L. tsangchanensis and L. muliensis were indistinguishable in the chemical composition and the ITS sequence, supporting a recent taxonomic study that merged the two species into L. tsangchanensis. Cacalol (1) was isolated as the most major component from both L. tsangchanensis and L. muliensis, while 6-acetoxy-9-oxofuranoeremophilane (10), a putative cacalol precursor, was isolated from the hybrid.

Terpenoids and Phenylpropanoids in Ligularia duciformis, L. kongkalingensis, L. nelumbifolia, and L. limprichtii

The diversity in root chemicals and evolutionally neutral DNA regions in the complex of Ligularia duciformis, L. kongkalingensis, and L. nelumbifolia (the d/k/n complex) was studied using eight samples collected in central and northern Sichuan Province of China. Cacalol (14) and epicacalone (15), rearranged eremophilanes, were isolated from the complex for the first time. Two new phenylpropanoids were also obtained. Seven of the eight samples produced phenylpropanoids and the other produced lupeol alone. Two of the seven samples also produced furanoeremophilanes or their derivatives and one produced oplopanes. The geographical distribution of the sesquiterpene-producing populations suggests that the production of sesquiterpenes evolved independently in separate regions. L. limprichtii collected in northern Sichuan was also analyzed and its chemical composition and the sequence of internal transcribed spacers (ITSs) in the ribosomal RNA gene cluster were found to be similar to that in the d/k/n complex and L. yunnanensis, which are morphologically similar.

Chemical constituents of hybrids of Ligularia cyathiceps and L. lamarum/L. subspicata collected in China: Structures of subspicatins M, N, O1, and O2, and related compounds

Three natural hybrids and an introgressed individual of Ligularia were evaluated based on a combination of morphology, root chemicals, and nucleotide sequences of evolutionally neutral regions to understand the chemical outcomes of hybridization and introgression. Six previously undescribed eremophilane sesquiterpenes were isolated from hybrids between L. cyathiceps and L. lamarum/L. subspicata, and benzofurans were isolated from L. subspicata for the first time. Their structures were elucidated based on spectroscopic analyses. Some compounds produced by hybrids have not been detected in either parental species, indicating that the metabolic profile was altered by hybridization and introgression.

[Diversity of Plants Belonging to the Genus Ligularia (Asteraceae) Based on Terpenoids and Synthetic Studies on Some Terpenoids]

The terpenoid constituents of Ligularia virgaurea (30 samples), Ligularia pleurocaulis (8 samples), Ligularia dictyoneura (8 samples), Ligularia brassicoides (5 samples), Ligularia lingiana (1 sample), and Ligularia liatroides (1 sample)(all belonging to section Senecillis of Ligularia, Asteraceae and collected in Yunnan, Sichuan, Qinghai, and Gansu provinces, China), from which 220 compounds were isolated, including 113 novel ones, are reviewed. Five chemotypes were identified in L. virgaurea based on their chemical constituents, while three clades were detected from the base sequences. Although intra-specific diversity was found in L. virgaurea, more samples were needed of other species in order to reach a definite conclusion. Inter-specific diversity was also examined in section Senecillis but was restricted due to the scarcity of samples. Synthetic studies on chiral natural products to determine their absolute configurations, especially those of riccardiphenols A and B as well as crispatanolide, which were all isolated from the liverwort, are briefly reviewed.

Chemical and Genetic Study of two Ligularia Hybrids in Shangrila County, Yunnan Province, China

The composition of root chemicals was examined for samples of L. cyathiceps × L. duciformis, L. duciformis × L. yunnanensis, and L. yunnanensis. Various furanoeremophilanes were isolated from a sample of L. cyathiceps × L. duciformis and found to be very similar to those isolated from L. cyathiceps. Lupeol and docosyl ferulate were isolated from L. yunnanensis, L. duciformis, and L. duciformis × L. yunnanensis.

Three New Eremophilanes from a Ligularia Hybrid Collected in China

Three new eremophilanes were isolated from a sample of Ligularia collected in Yunnan province of China and their structures were determined. The chemical constituents including eleven eremophilanes (major constituents: 6-acyloxyfuranoeremophilan-10β-ols) were similar to those of a hybrid of L. cyathiceps and L. subspicata, however, the base sequence of the ITS1-5.8S-ITS2 region was typical of L. cyathiceps, indicating backcrossing.

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.

Diversity in Chemical Constituents of Ligularia Longihastata Collected in China

Root constituents of Ligularia longihastata were examined for the first time. Fourteen eremophilane sesquiterpenes, including two new eremophilanes identified as 3α-isobutyroyloxy-7β H-eremophila-9,11-dien-8-one and 3β-angeloyloxy-1β,10β-epoxyfuranoeremophilan-9-one, and three eudesmanes were isolated. From samples collected in Baiyu County, Sichuan Province, furanoeremophilane derivatives were isolated, while various eremophilan-8-ones were isolated from samples collected in Kangding County, Sichuan. The results suggest chemical diversity in the species.

Chemical Constituents of Ligularia Wilsoniana Collected in Chongqing, China

The chemical constituents of Ligularia wilsoniana were studied for the first time, using four samples collected in Chongqing City, China. Two new compounds, 6β-(2′,3′-epoxy-2′-methylpropanoyloxy)-1β,10β-epoxyfuranoeremophilane and 11αH-6β-(2′-hydroxymethylacryloyloxy)-1β,10β;7β,8β-diepoxyeremophilanolide, as well as eight known compounds, were isolated from one of the samples, while three to four known furanoeremophilanes were isolated from the other three samples. No compound was common to the two classes of the samples, demonstrating the presence of at least two chemotypes of this species.

Chemotypes of Ligularia vellerea, its Hybrids, and L. melanothyrsa

Ligularia vellerea and L. melanothyrsa have been found to share chemical characteristics based on geography. In one chemotype (Shangrila type), the major components were either 15-oxygenated furanoeremophilanes or eremophilanolides; and in another (Luguhu type), either 1-angeloyloxyfuranoeremophilanes or corresponding lactones. The two L. vellerea samples were found to have experienced hybridization with either L. cyathiceps or L. kanaitzensis; however, compounds typical of L. vellerea alone were isolated from them.

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.

[Chemical and genetic diversity of Ligularia plants collected in the Hengduan Mountains, China]

The Hengduan Mountains area of China is rich in plant resources. The Ligularia species, which belong to Senecioneae and Asteraceae, distributed in this area are highly diversified and contain 6 sections and over 100 species, and are considered to be in on-going evolution and diversification. To understand the inter- and intra-specific diversity of these plants and to elucidate the mechanism of diversification, we analyzed Ligularia plants by chemical, genetic, geographical, ecological, and morphological approaches. We investigated 4 species, and isolated 26 novel compounds. Based on the chemical composition of root extract as well as nucleotide sequence variations in internal transcribed spacers (ITS), we obtained 3 findings. (i) L. virgaurea is classified into two groups, ligularol type and virgaurenone type from the view point of chemical constituents, which are phylogenetically distinguished from each other, (ii) L. subspicata and L. lamarum have an overlapped chemical spectrum, but showed no clear genetic correlation, and (iii) L. cyathiceps showed no significant variations in either chemical constituents or nucleotide sequences.

Four New Bisabolane-type Sesquiterpenes from

The chemical constituents of the roots of two Ligularia lankongensis samples collected in Yunnan and Sichuan Provinces, China, were investigated, together with the DNA sequence of the atpB-rbcL and ITS regions. Four new highly oxygenated bisabolane-type sesquiterpenes (1 – 4) were obtained. Intraspecific diversity in the DNA sequence was found to be limited.

Four New Guaianolides and Acetylenic Alcohol from Saussurea Katochaete Collected in China

Four new guaianolides and an acetylenic alcohol were isolated from Saussurea katochaete (Asteraceae) collected in China. The structures were determined based on the spectroscopic data including the absolute configuration by application of advanced Mosher's method.

Complex Diversity in

Two samples of Ligularia kanaitzensis collected in the Shizhongshan Mountain region of Yunnan Province, as well as one sample collected in Sichuan Province, were analyzed with regard to root constituents and neutral DNA sequences. The two Shizhongshan samples were found to be different from each other and from other samples analyzed previously, indicating that the intra-specific diversity in the species was highly complex.

Diversity of Furanoeremophilanes in Major Ligularia Species in the Hengduan Mountains

The chemical and genetic diversity of Ligularia species in the Hengduan Mountains area of China is reviewed. A hypothesis that the production of furanoeremophilanes is ecologically advantageous is proposed.

Four New Eremophilane-Type Alcohols from Collected in China

Four new eremophilane-type sesquiterpenoid alcohols were isolated from Cremanthodium helianthus collected in China and their structures established on the basis of spectroscopic analyses. All of them had 9-en-8-one partial structures with one more double bond either Δ11, Δ11(13), or Δ7(11). Two of them had a hydroxy group at C-1 position.

Four eremophil-9-en-8-one derivatives from Cremanthodium stenactinium samples collected in China

Two samples of Cremanthodium stenactinium (Asteraceae) were collected in Sichuan Province, China. From the ethyl acetate extracts of the roots, three new eremophilane-type sesquiterpenoids and one new trinoreremophilane compound were isolated, together with other known eremophilanes. Their structures were determined based on the spectroscopic data. This is the first report of isolation of eremophilane-type compounds from the genus Cremanthodium.

Chemical Diversity of Iridal-Type Triterpenes in Iris Delavayi Collected in Yunnan Province of China

From Iris delavayi collected in the northwestern Yunnan Province of China, eight iridal-type triterpenoids were isolated, three of which were new. Both 2(7) Z- and 2(7 )E-iridals were isolated in about equal amounts from the sample collected at Laojunshan, while only 2(7 )Z-iridals were isolated from samples collected in Shangrila area, indicating the presence of chemical diversity in the species.

Two New Furanoeremophilane Sesquiterpenoids from: Ligularia oligonema

From the roots of Ligularia oligonema and an unidentified sample of Ligularia collected in Yunnan Province of China, two new sesquiterpenoids, 3β-acetoxy-6β-(2-methylbutyryloxy)furanoeremophilan-10β-ol and 3β-acetoxy-6β-isobutyryloxy-furanoeremophilan-10β-ol, were isolated. DNA sequencing showed that the unidentified sample was likely to be L. oligonema. In addition, the DNA data suggested that the chemical evolution among L. oligonema and related Ligularia species is rather complex.