Cycloartane-type triterpenoids from Astragalus hoantchy French.

Abstract A new cycloartane-type triterpenoid, 3β-acetoxy-9β,19-cyclolanost-24E-ene-1α,16β-diol-27-O-β-d-glucopyranoside (1), together with three known ones (2–4) were isolated from the aerial parts of Astragalus hoantchy. The structure of compound 1 was elucidated by detailed spectroscopic analyses including 1D and 2D NMR, HRESIMS, and IR experiments. All of the four compounds were isolated from A. hoantchy for the first time. The antifungal activities of compounds 1–4 against a phytopathogenic fungus (Alternaria solani) were evaluated with the result that compound 3 exhibited a moderate activity with an IC50 value of 284 μg/mL.


Introduction
Astragalus L., the largest genus of the family Leguminosae, is well known for its various medicinal applications as antiperspirant, immunostimulant, hepatoprotective, diuretic, antidiabetic and anticarcinogen worldwide (Krasteva et al. 2010;Sevimli-Gür et al. 2011;Feng et al. 2012;Nalbantsoy et al. 2012). As a perennial herb of this genus, Astragalus hoantchy is widely distributed in the north and northwest of China and has been used in traditional Chinese medicine and Mongolian medicine for centuries (Zhao et al. 2003;Guo et al. 2016). The chemical constituents of the genus Astragalus have been elaborately investigated in previous studies, which mainly contain saponins, flavonoids, polysaccharides and amino acids (El-Mawla 2010;Fathiazad et al. 2010;Ibrahim et al. 2012;Lim et al. 2015;Maamria et al. 2015).

General experimental procedures
IR spectra were measured on a Nicolet NEXuS 870 FT-IR spectrometer. optical rotations were obtained by a Perkin-Elmer 341 digital polarimeter. HRESIMS data were measured through a Bruker micoToF-QII mass spectrometer. 1D and 2D NMR spectra were recorded by CD 3 oD using a Bruker AM-400BB instrument with TMS as internal standard. Column chromatography (CC) was carried out on silica gel (200−300 mesh, Qingdao Haiyang Chemical Co, Ltd, Qingdao, China), Sephadex Pharmacia Fine Chemical Co,Ltd,Berlin,Germany),Mitsubishi Chemical Industries,Ltd). Standard thin-layer chromatography (TLC) was performed on silica gel (GF 254 , 10−40 μm; Qingdao Haiyang Chemical Co, Ltd). Spots on TLC were detected under uV light or by heating after spraying with 5% H 2 So 4 in C 2 H 5 oH (v/v).

Plant material
The aerial parts of A. hoantchy French. were collected in october 2014 in Anyang, Gansu Province, China. The plant was identified by Professor Huanyang Qi from Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences (CAS). A voucher specimen (Ah-P-01) was deposited in Lanzhou Institute of Chemical Physics, CAS.

Antifungal activity assay
A. solani (a phytopathogenic fungus, could cause destructive diseases in tomatoes and potatoes) was applied to evaluate the antifungal activity of compounds 1-4 in vitro by measuring the radial growth of mycelia . The compounds were dissolved in DMSo as stock solutions, then diluted with potato dextrose agar (PDA) medium to a testing concentration of 200 μg/mL and poured into the sterilized Petri dishes (diameter: 6 cm). After solidification, a mycelia disk (diameter: 0.6 cm) was inoculated in the centre of each dish. Then the dishes were sealed with parafilm and incubated at 25 °C in dark for 4 days. The same volume of DMSo was added to PDA medium as control and three replicates were carried out to every measurement. Compound 3 was further measured under concentrations (400, 200, 100 and 50 μg/mL) to calculate the IC 50 value.

Conclusion
A. hoantchy is a medicinal plant used in traditional Chinese and Mongolian medicine. In this paper, one new cycloartane-type triterpenoid (1) and three known ones (2-4) were isolated from the aerial parts of A. hoantchy. Their antifungal activities were evaluated against a phytopathogenic fungus (A. solani), and compound 3 exhibited a moderate antifungal activity with the IC 50 value of 284 μg/mL. All the compounds were discovered from A. hoantchy for the first time.