A new cycloartane triterpene glycoside from Souliea vaginata

Abstract A new cycloartane-type triterpene glycoside, namely soulieoside M (1), and one known compound, beesioside I (2), were isolated from the ethanolic extract of the rhizomes of Souliea vaginata. Their structures were determined spectroscopically and compared with previously reported spectral data. Compounds 1 and 2 were evaluated for their cytotoxic activities against three human cancer cell lines.


Introduction
Souliea vaginata (Maxim.) Franch. (Ranunculaceae) is a perennial herb mainly native to the mountains of Gansu, Shanxi and Yunnan provinces of China and is traditionally used as Chinese folk medicine for the treatment of conjunctivitis, stomatitis, pharyngitis and enteritis (Institute of Botany, Chinese Academy of Sciences & Institute of Materia Medica, Chinese Academy of Medical Sciences 1979). Previous phytochemical investigations on this plant ABSTRACT A new cycloartane-type triterpene glycoside, namely soulieoside M (1), and one known compound, beesioside I (2), were isolated from the ethanolic extract of the rhizomes of Souliea vaginata. Their structures were determined spectroscopically and compared with previously reported spectral data. Compounds 1 and 2 were evaluated for their cytotoxic activities against three human cancer cell lines. have disclosed the presence of cycloartane triterpene glycosides as the characteristic components of the genus Souliea (Sakurai et al. 1986;1990, 1993Takao et al. 1985;Zhou et al. 2004;Zhou, Yang, Wu et al. 2005;. Cycloartane triterpene glycosides with variable polycyclic skeletons show diverse biological activities including anti-complement, antitumour and cholinesterase enzymes inhibitory effects (Mohamed 2014;Jamila et al. 2015;Satiraphan et al. 2015;Zhao et al. 2016). In the course of our search for novel antitumour agents, a new cycloartane-type triterpene glycoside, soulieoside M (1), and one known compound, beesioside I (2), were isolated from the ethanolic extract of the rhizomes of S. vaginata (Figure 1). Herein, we report their isolation, structure elucidation and cytotoxic activities.
Besides, beesioside I (2) was obtained and identified by comparing its spectroscopic data with those reported in the literature.
The cytotoxicity of compounds 1 and 2 was assayed against three human cancer cell lines (HT-29, A549 and MDA-MB231) using the MTT method with 5-Fu as the positive control. The results showed that compounds 1 and 2 exhibited moderate cytotoxic activity against all the tested cell lines with IC 50 values of 17.3−64.7 μM (Table S2).

Plant material
The

Acid hydrolysis of compound 1
Compound 1 (2 mg) was heated in 2 ml of 2 M trifluoroacetic acid at 95 °C for 2 h. The reaction mixture was extracted three times with 2 ml of CHCl 3 . The remaining aqueous layer was concentrated to dryness with etoH to give a residue, and the residue was dissolved in anhydrous pyridine (2 ml). The sugar was derivatised with l-cysteine methyl ester hydrochloride (3 mg, 60 °C, 1 h) and subsequently silylated with hexamethyldisilazane and chlorotrimethylsilane (Fluka) (2:1, 1.5 ml; 60 °C, 30 min). Finally, the supernatant (0.5 ml) was analysed by GC-MS (Agilent 7890A/5975C, Agilent Technologies, Santa Clara, CA, uSA) under the following conditions: capillary column HP-5 (30 m × 0.25 mm × 0.25 μm); temperature gradient: 150 °C for 2 min, then 5 °C/min to 210 °C; carrier, helium gas (1.0 ml/min); and injection volume: 1.0 μl. The injection and detector temperature were set at 290 °C, and the splitting ratio was 1/10. The presence of d-xylose in the acid hydrolysate of 1 was confirmed by comparison of their respective retention times with those of standard sample. The retention times (t R , min) of d-xylose were 8.18 and 9.12 min.

Cytotoxic assays
The cytotoxicity of compounds 1 and 2 was assessed against HT-29, A549 and MDA-MB231 human cancer cell lines by the MTT method. HT-29 cells were grown in RPMI 1640 medium, MDA-MB231 and 549 cells in DMeM, supplemented with 10% v/v FBS and 1% penicillinstreptomycin solution, and were cultured at a density of 2 × 10 4 cells/ml per well in a 96-well microtiter plate (Corning, Suzhou, China) and incubated overnight at 37 °C in a humidified atmosphere of 95% air and 5% Co 2 . Then, the cells were treated with test samples for 24 h. After removing the supernatant of each well, a total of 10 μl of MTT solution was added to each well at the time of incubation for 4 h. The formazan crystals in each well were dissolved in lysis buffer for overnight at 37 °C. The absorbance at 550 nm was measured by an Infinite M200 Pro spectrophotometer (Tecan, Switzerland). The data are expressed as the percentage of the control optical density (oD) values for each experiment.

Supplementary material
Supplementary material relating to this paper is available online, alongside Table S1 and S2, and Figures S1-S8.

Disclosure statement
No potential conflict of interest was reported by the authors.