A new sesquiterpene lactone from the leaves of Panax vietnamensis Ha et Grushv. (Vietnamese ginseng)

Abstract Panax vietnamensis (Vietnamese ginseng, Ngoc Linh ginseng) is an endemic Panax species of Vietnam. From the methanol extract of the leaves of Panax vietnamensis, five compounds (1–5) were isolated, including one new sesquiterpene lactone such as panaxolide (1) and four known compounds. The structures of the compounds (1-5) were elucidated by spectral techniques such as 1 D NMR (1H NMR, 13C NMR), 2 D NMR (COSY, HSQC, HMBC, NOESY) and mass spectrometry. The absolute configuration of 1 was determined based on the Cotton effects in the CD spectrum. All of the five compounds were screened for their in vitro growth inhibitory activities against cancerous cells (HepG2) and normal cells (fibroblast) using the SRB assay. Panaxolide (1) showed the highest potential for the growth inhibition of cancerous cells HepG2 with the IC50 values of 63.8 μM. Graphical Abstract


Introduction
Ng _ oc Linh is a 2598 meters high mountain range of the South Annamite Range in Central Vietnam.It stretchs over four provinces of Kon Tum, Quang Nam, Quang Ngai, and Gia Lai.In 1973, a new wide Panax species was discovered in the Ngoc Linh mountain at 1800 meters above sea level belongs to Kon Tum province.In 1985, its scientific name was officially named as Panax vietnamensis Ha et Grushv., Araliaceae (Nguyen et al. 1993;1995;Tran et al. 2001).Panax vietnamensis is an endemic Panax species which was distributed in Ngoc Linh mountain range only.Until now, in Vietnam, there were many researchs for cultivating this plant in other areas but the results are still not good.Vietnamese ginseng and Ngoc Linh ginseng are both of the same popular name of this plant (Komatsu et al. 2001;Le et al. 2018).
Panax vietnamensis (Vietnamese ginseng) is very enrich saponins in the chemical constituents of all parts, in rhizomes, roots and leaves even.It contains more saponins than other Panax species in the world such as Panax ginseng (Korean ginseng), Panax quinquefolium (American ginseng), Panax notoginseng (Chinese ginseng) and a large quantity of ocotillol-type saponins that are not present in Panax ginseng (Korean ginseng).Up today, there are 63 saponin compounds which were isolated from rhizomes, roots and leaves of Vietnamese ginseng (Nguyen et al. 1993;1994a, 1994b;1997;Tran et al. 2002;Banskota et al. 2003;Le et al. 2015).In addition to saponins, the composition of polyacetylenes (Lutomski and Tran 1989;1991), flavonoids, acylquinic acids (Chirikova et al. 2019) was also studied.In traditional medicine, Vietnamese ginseng is well known as a medicinal plant for treatment of many serious diseases and specially effective for physical enhancement.The clinical studies have showed that Vietnamese ginseng exhibits many activities such as antifatigue, antidiabetic, antioxidant, antibacterial, anti-stress, antihypertensive, analeptic, adaptogenic, gonadotropic, … .( Yamasaki 2000;Banskota et al. 2003;Nguyen et al. 2005;Le et al. 2014).There were many publications on rhizomes, roots but few on leaves.

Biological tests
The compounds were screened initially at 200 mM against cancerous cells (HepG2) and noncancerous cells (human fibroblast).Camptothecin was used as a positive control, with IC 50 values against HepG2 0.23 lM and 4.51 lM against fibroblast.The results indicated that there is only new compound, panaxolide (1), showed the highest and remarkable growth inhibitory value of 93.32% against HepG2 and 49.84% against fibroblast.The remaining compounds (2-5) with growth inhibitory percent values lower than 50%, did not show growth inhibition (Table S13, S14 and Diagram S14 Ã ).Panaxolide (1) was further assessed for IC 50 value at the concentration range 10-200 mM.The result showed the IC 50 value against HepG2 63.8 lM, while greater than 200 lM on fibroblast (Table S15 and Diagram S15 Ã ).

Plant material
The leaves of Panax vietnamensis (Vietnamese ginseng) were collected in October 2019 in Kon Tum province, Vietnam and were authenticated by Botanist Viet Hoang, Department of Ecology -Evolutionary Biology, Faculty of Biology -Biotechnology, VNUHCM-University of Science, Ho Chi Minh City.A voucher specimen (PV 2019) has been deposited at the Department of Organic Chemistry, Faculty of Chemistry, VNUHCM -University of Science.
Compound 1 was isolated as a white amorphous powder.The molecular formula of C 15 H 22 O 4 was assigned for this compound based on HR-ESI-MS analysis ([M-H] -m/z 265.1477; calcd.for [C 15 H 21 O 4] -, 265.1445).