Polysciosides J and K, two new oleanane-type triterpenoid saponins from the leaves of Polyscias fruticosa (L.) harms. cultivating in An Giang Province, Viet Nam

Abstract For the first time, the phytochemical constituents of the leaves of Polyscias fruticosa (L.) Harms. cultivating in An Giang Province, Viet Nam were investigated and led to purify two new oleanane-type triterpenoid saponins, named polyscioside J (1) and polyscioside K (2) together with two known saponins, ladyginoside A (3) and chikusetsusaponin IVa (4) using variously chromatographic methods. Saponin (4) was reported for the first time from this species. Their structures were verified by IR, UV, HR-ESI-MS, NMR 1D and 2D experiments and compared with previous literatures. Graphical Abstract


Introduction
Polyscias is the second largest genus in the family Araliaceae, with 159 species and is distributed from tropical Africa to the islands of the eastern Pacific Ocean (Bean 2015), which 7 species and 1 variety are found in Vietnam (La et al. 2013). Polyscias fruticosa has been used traditionally in Vietnam for the treatment of ischemia, inflammation and increase blood in the brain (Do 2004;Vo 2012). Pharmacological investigation of extracts from P. fruticosa possessed anti-asthmatic, anti-inflammatory (Bernard et al. 1998;Koffuor et al. 2014Koffuor et al. , 2016; anti-histaminic, mast cell stabilization effect (Koffuor et al. 2016); anti-pyretic, anagesic, molluscicidal properties (Bernard et al. 1998), diuretic effect (Varadharajan and Rajalingam, 2011), anti-diabetic activity (Divakar and Bensita, 1998;Hanh et al. 2016). Phytochemical study of P. fruticosa illustrated triterpenoid saponins (Chaboud et al. 1995;Proliac et al. 1996;Hanh et al. 2016), and polyacetylens (Lutomski et al. 1992) as the main ingredients. Moreover, steroids (Tram et al. 2017) and sesquiterpenoids (Brophy et al. 1990) were reported. Continuing a study of the bioactive triterpenoids (Nguyen et al. 2015(Nguyen et al. , 2016Ngo et al. 2017Ngo et al. , 2018, this paper concentrates the isolation and structural elucidation of two new oleanane-type triterpenoid saponins (1, 2) and two known saponins from the leaves of P. fruticosa cultivating in An Giang Province, Viet Nam.

General experimental procedures
The optical rotations were determined on a Kr€ uss-optronic GmbH polarimeter equipped with a sodium lamp (589 nm) (Hamburg, Germany). The IR spectra were recorded with a Bruker Tensor 27 FT-IR Spectrometer (Bremen, Germany). The UV spectra were performed with Agilent 1260 HPLC-UV (Waldbronn, Germany). The high resolution electrospray ionisation mass spectroscopy (HR-ESI-MS) was recorded on a LC-X500R QTOF spectrometer (Sciex, USA). The 1 H-NMR (500 MHz), 13 C-NMR (125 MHz), DEPT, COSY, HSQC and HMBC spectra were recorded on a Bruker AM500 FT-NMR spectrometer using tetramethylsilane (TMS) as internal standard (MA, USA). Column chromatography was carried out using Merck Silica gel normal-phase (230-240 mesh) and reversed-phase C 18 Merck (Darmstadt, Germany). Analytical TLC was carried out in silica gel plates Merck DC-Alufolien 60 F 254 (Darmstadt, Germany). Compounds were visualized by spraying with aqueous 10% H 2 SO 4 and heating for 3-5 min. Camptothecin was purchased from Calbiochem.

Plant material
The leaves of Polyscias fruticosa were cultivated in An Giang Province, Viet Nam and identified by Prof. Dr. C.L. Tran, Nursing Pharmaceutical Sciences, Tay Do University. A voucher specimen (No. Mai-PF-2016) was deposited in Nursing Pharmaceutical Sciences, Tay Do University.

Extraction and isolation
Dried powder of leaves P. fruticosa (859 g) were extracted with 96 EtOH for three time (3 Â 10 L) at room temperature, residue was filtered, solvents were removed under low pressure and the crude extract was obtained. The crude extract (156 g) was applied to liquid-liquid extraction procedures and successively partitioned into diethyl ether, ethyl acetate, n-butanol and aqueous partition. The n-butanol extract (50 g) was eluted by Diaion HP-20 column with H 2 O, 50% MeOH, 80% MeOH, 100% MeOH and 100% Me 2 CO to give five major fractions (I-V), respectively. Fraction III (11 g) was subjected to silica gel normal-phase column chromatography with mobile phase CHCl 3 -MeOH gradient (0-100%) to get five subfractions (III.1-III.5).

Disclosure statement
No potential conflict of interest was reported by the author(s).

Funding
This research is funded by An Giang Department of Science and Technology.