Eudesmane-Type Sesquiterpene Glycosides from Dictamnus dasycarpus Turcz.

Eudesmane-type sesquiterpenes have been reported to exhibit varieties of biological activities. During the process of investigating this kind of natural product from the root bark of Dictamnus dasycarpus Turcz., 13 eudesmane-type sesquiterpene glycosides including six new isolates, named as dictameudesmnosides A1 (1), A2 (2), B (3), C (4), D (5), and E (6), together with seven known ones (7–13), were obtained. Herein, their structures were determined by the analysis of physical data, spectroscopic analysis, and chemical methods. The existence of α-configuration glucose units in their structures (1–5, 8) is not very common in natural glycosidic components. Meanwhile, compounds 3–5, 7, and 9–13 displayed TG accumulation inhibitory effects on HepG2 cells.

The root bark of Dictamnus dasycarpus Turcz., also known as Cortex Dictamni, belongs to the Rutaceae family. It is a plant rich in eudesmane-type sesquiterpenes [7,8]. As a traditional Chinese medicine, D. dasycarpus has been commonly used in the treatment of inflammation, microbial infection, pruritus vulvae, eczema, scabies, cancer, and other diseases in China for thousands of years because of its abilities to arrest itching, clear away heat, and eliminate dampness [9]. In addition, the decoction could effectively inhibit body weight and fat content increase caused by high fat diet, reduce triglyceride (TG) and total cholesterol contents in blood, and alleviate obesity [10].
The structures of known compounds 7-13 were identified by comparing their 1 H and 13 C-NMR data with those of references.

General
Optical rotations were measured on a Rudolph Autopol ® IV automatic polarimeter (l = 50 mm) (Rudolph Research Analytical, Hackettstown, NJ, USA). IR spectra were recorded on a Varian 640-IR FT-IR spectrophotometer (Varian Australia Pty Ltd., Mulgrave, Australia). NMR spectra were determined on a Bruker 500 MHz NMR spectrometer (Bruker BioSpin AG Industriestrasse 26 Cell culture: HepG2 cells were routinely cultured in DMEM-based medium as described before [13]. After cells reached about 80% confluence, seeded at a density of 80,000 cells/mL in 48-well plates for 24 h, the experiments were performed. Sodium oleate-induced lipid accumulation: To induce the overloading of intracellular lipid, SO was used as previous reported. Briefly, after being seeded in 48-well plates in FBS-free medium for 24 h, HepG2 cells were exposed to 200 µM SO in the presence or absence of isolates (30 µM) or the positive control, orlistat (5 µM), for another 48 h. The intracellular TG content was finally examined using a commercial assay kit at 492 nm after cells were rinsed with phosphate-buffered saline (PBS).
Statistical analysis: Values are expressed as means ± S.D. All of the grouped data were statistically analyzed with SPSS 11.0. Significant differences between means were evaluated by one-way analysis of variance (ANOVA), and Tukey's Studentized range test was used for post hoc evaluations. p < 0.05 was considered to indicate statistical significance.

Conclusions
In conclusion, 13 eudesmane-type sesquiterpene glycosides have been isolated from the 70% EtOH extract of D. dasycarpus root bark. Their structures have been determined on the basis of spectroscopic and chemical analyses. The existence of the α-configuration glucose units in their structures (e.g., 1-5, 8) is not very common in natural glycosidic components.
On the other hand, as one of main constituents of D. dasycarpus root bark, the eudesmane-type sesquiterpene glycosides, isolates 3-5, 7, and 9-13, showed significant TG accumulation inhibitory activity, which was identical to the information reported by Kim et al. that the decoction could reduce TG and total cholesterol contents in blood as well as alleviate obesity effectively [10]. In addition, we can deduce that D. dasycarpus is one of potential active plants for improving metabolic disease.