Isolation and structure determination of the second toxic constituent from Tetradymia glabrata

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.

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.

Phytotoxic Terpenoids from Ligularia cymbulifera Roots

Ligularia cymbulifera is one of the predominant species in the Hengduan Mountains, China, and has led to a decrease in the amount of forage grass in this area. However, little is known about the mechanism behind its predominance. In this study, two novel eremophilane sesquiterpenes, ligulacymirin A and B (1 and 2), together with seven other known terpenoids (3-9), were isolated from the roots of L. cymbulifera. The structures of 1 and 2 were determined by spectroscopic methods and single-crystal X-ray diffraction. Each compound showed phytotoxic activities against Arabidopsis thaliana, and each was detected and identified in rhizosphere soil by UHPLC-MS. Compound 3 was the most potent phytotoxin, showing remarkable inhibition against both seedling growth (EC₅₀ = 30.33 ± 0.94 μg/mL) and seed germination (EC₅₀ = 155.13 ± 0.52 μg/mL), with an average content in rhizosphere soil of 3.44 μg/g. These results indicate that terpenoids in L. cymbulifera roots might be released as phytotoxins in rhizosphere soil to interfere with neighboring plants.

Phytotoxic Eremophilanes from Ligularia macrophylla

Systematic bioassay-guided fractionation of the methylene chloride extract of the roots from Ligularia macrophylla was performed to identify both phytotoxic and antifungal compounds. Four phytotoxic eremophilanes (furanoeremophilan-14beta,6alpha-olide, 6beta-angeloyloxy-10beta-hydroxyfuranoeremophilane, eremophil-7(11)-ene-12,8alpha;14beta,6alpha-diolide, and 3alpha-angeloyloxybakkenolide A) and two antifungal fatty acids (linoleic acid and alpha-linolenic acid) were isolated. The X-ray crystal structure determination of 6beta-angeloyloxy-10beta-hydroxyfuranoeremophilane is reported here for the first time. All four eremophilanes substantially inhibited growth of the monocot Agrostis stolonifera (bentgrass) while demonstrating little activity against the dicot Lactuca sativa (lettuce) at 1000 microM. In a dose-response screening of all compounds for growth inhibitory activity against Lemna paucicostata, 6beta-angeloyloxy-10beta-hydroxyfuranoeremophilane was the most active with an IC50 of 2.94+/-0.16 microM. This compound also caused the greatest reduction of photosynthetic electron flow; however, its mode of action remains to be determined. Evaluation of isolated compounds for activity against the Formosan subterranean termite, Coptotermes formosanus, is also reported. At a concentration of 0.5% (wt/wt), 6beta-angeloyloxy-10beta-hydroxyfuranoeremophilane significantly reduced the consumption of filter paper by C. formosanus.