Sesquiterpenes from the Roots ofLigularia duciformis

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.

New Oplopane-type Sesquiterpenoids from Ligularia duciformis

The chemical constituents of the root of Ligularia duciformis, collected in Yunnan Province of China, was studied and two new oplopane-type sesquiterpenoids were isolated, whose structures were determined on the basis of spectroscopic evidence. Quite recently, oplopane-type compounds were found in Ligularia narynensis, and this is the second example to isolate oplopane-type sesquiterpenoids from Ligularia plants.

The First Isolation of Furanoeremophilane from Ligularia nelumbifolia

Ligularol (1), a furanoeremophilane, was isolated together with eremophil-1(10)-en-11-ol (2) from one of eight collected samples of Ligularia nelumbifolia and L. kongkalingensis, a closely related species. It is proposed that the ability to produce the furanoeremophilane has been acquired through hybridization.

Chemical and genetic study of Ligularia duciformis and related species in Sichuan and Yunnan Provinces of China

The chemical constituents of the root extracts and the evolutionarily neutral DNA base sequences were studied for 28 samples of Ligularia duciformis, L. kongkalingensis, and L. nelumbifolia collected in Sichuan and Yunnan Provinces of China. The samples could be classified into four chemotypes (1-4). Sesquiterpenoids having eremophilane and oplopane skeletons were isolated from two (Chemotype 1) and three (Chemotype 2) samples, respectively. Two new oplopane derivatives were isolated and their structures were determined. In 18 samples, phenylpropenoids were the major components (Chemotype 3). In five samples, neither phenylpropenoids nor sesquiterpenoids were found (Chemotype 4). Despite this large chemical variety, no correlation was found between the chemotype and the morphological criteria of species identification. The analysis of the evolutionarily neutral DNA regions also indicated that the samples were not separated into distinct clades and that introgression was extensive.

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.

Eudesmane sesquiterpenoids from the Asteraceae family

This review covers the structures and biological activities of eudesmane-type sesquiterpenoids from the plants of the Asteraceae family. Biosynthetic studies or chemical syntheses leading to the revision of structures or stereochemistries have also been included, and 593 references are cited.