Four sesquiterpenes isolated from Taraxacum mongolicum

Abstract One new sesquiterpene, (6S,7R,11S)-13-carboxy-1(10)-en-dihydroartemisinic acid (1), together with three known sesquiterpenes, ainsliaea acid B (2), mongolicumin B (3), and 11β,13-dihydroxydeacetylmatricarin (4) were isolated from Taraxacum mongolicum Hand.-Mazz. The structures were established on the basis of UV, IR, HR-ESI-MS, 1D and 2D NMR spectroscopy, ECD spectroscopy, and X-ray diffraction analysis. Compound 1 was found to have potential anti-inflammatory activity and could reduce LPS-induced NO levels in murine macrophage, with inhibitory rate of 37%.


Introduction
Dandelion (Taraxacum mongolicum Hand.-Mazz.) is a perennial herbaceous plant belonging to the Compositae family.Taraxacum genus, consisting of more than 3000 species, originated from central Asia and grows almost anywhere worldwide [1][2][3].T. mongolicum, a famous traditional Chinese medicine and an edible medicinal herb, is primarily used for the treatment of inflammatory disorders and viral infectious diseases.Phenolic compounds, sesquiterpenes, flavonoids, and polysaccharides are the main bioactive metabolites found in T. mongolicum [4,5].

Results and discussion
Compound 1 showed potential anti-inflammatory activity, which could significantly reduce LPS-induced NO levels in murine macrophage with inhibitory rate of 37% at 10 lM.

X-ray diffraction data analysis
The X-ray diffraction data (1) were obtained on a Rigaku XtaLAB Synergy diffractometer equipped with a hybrid photon counting CCD detector (Hypix 6000) using CuKa radiation and a graphite monochromator.The sample crystal was cooled to 100.01 K using a cold nitrogen stream.Data reduction, cell refinement and experimental absorption correction were performed in CrysAlisPro.The structural solution, refinement, and data output were performed with the OLEX2 program package using SHELXL-2014 for refinement.The multiscan method was used for the absorption correction.Structures were solved and refined against F 2 by full-matrix least-squares.Hydrogen atoms were generated geometrically at idealized positions and constrained to ride on their parent atoms.All nonhydrogen atoms were refined anisotropically.

Anti-inflammation evaluation
Anti-inflammation assay for compounds 1À4 was carried out in accord with the methods reported in the literature [9].
The dried herb of Taraxacum mongolicum Hand.-Mazz.(Compositae) was purchased from Tong Ren Tang Pharmaceutical Company in Beijing, China in August 2019.It was identified by associate Professor Lin Ma of the Institute of Materia Medica, Chinese Academy of Medical Science and Peking Union Medical College, China.A voucher specimen (ID-S-2951) was deposited at the Institute of Materia Medica, Chinese Academy of Medical Science, and Peking Union Medical College, China.

Table 1 .
The 1 H and 13 C NMR spectral data of compound 1 in methanol-d 4 (500 MHz for 1 H NMR and 100 MHz for 13 C NMR).