Aralianudaside A, an unusual skeleton triterpenoid saponin with anti-airway inflammatory activity from Aralia elata

Abstract Aralianudaside A, a triterpene saponin with an unusual skeleton of pentacyclic triterpenoid, along with a new triterpene glycoside and six known compounds were obtained from the buds of Aralia elata. Their structures were determined through extensive spectral analysis, including HRESIMS, IR, 1D and 2D NMR, glycolysis and GC. All compounds were evaluated for anti-airway inflammatory activity in lipopolysaccharides (LPS)-induced airway epithelial cells (16HBE), compounds 1, 3, 5, 7 and 8 significantly decreased the expression of pro-inflammatory cytokines IL-1β and IL-4. Graphical Abstract


Introduction
There were more than 70 species of the genus Aralia in the world, mainly distributed in Asia.China was rich in Aralia genus resources, as many as 30 species (The Flora of China 1978).Triterpene saponins from the genus Aralia were the main components, including oleanane-type and ursane-type (Clement and Clement 2015), which exhibited a variety of physiological activities, such as anti-inflammatory (Hong et al. 2018;Yen et al. 2022), hypoglycemic (Suh et al. 2007;Cui et al. 2013), anti-tumour (Weng et al. 2014;Choi et al. 2015) and other activities.Aralia elata (Miq.)Seem.was a plant of the genus Aralia of the family Araliaceae, and its buds were often eaten as wild vegetables, with the function of activating blood and dissolving stasis, dispelling wind and dampness, used for the treatment of wind fever cough and asthma, dysentery, rheumatism and pain in the folk (Yin et al. 2022).In order to further replenish its information, an ongoing research for bioactive constituents from this plant was carried out, which obtained a novel skeleton of pentacyclic triterpenoid (1) and a new triterpene saponin (2), together with six known triterpene glycosides (3-8) (Figure 1).In addition, the anti-airway inflammatory activity of compounds 1-8 was evaluated.

Results and discussion
Compound 1 was a white powder.The HRESIMS showed an excimer ion peak of m/z 683.4383 [M + HCoo] -(calcd for [C 36 H 62 o 9 +HCoo] -, 683.4376), corresponded to molecular formula was C 36 H 62 o 9 .The characteristic absorption peak of hydroxyl (3424 cm −1 ) can be observed in IR spectrum.
In the experiment of CCK-8, there were no significant effects on cell viability of compounds 1-8 at the concentration of 12 μM (Figure S24, supplementary materials).In anti-airway inflammatory screening section, compounds 1, 3, 5, 7 and 8 markedly inhibited the secretion of IL-1β and IL-4 in LPS-induced 16HBE, among them, 1 revealed the best activity (Figure 3).

Plant material
The buds of A. elata were collected in April, 2019 from Lushui County, Nujiang Lisu Autonomous Prefecture, Yunnan Province, were identified as A. elata by Prof. Yan-ping Li (College of Traditional Chinese Medicine, Yunnan university of Chinese Medicine).A voucher specimen (201904SM) was deposited in the Yunnan Key Laboratory of Dai and Yi Medicine, Yunnan university of Chinese Medicine.

Sugar identification
Compounds 1-2 (each 3.0 mg) added 10 mL of HCl (2 mol/L), heated under reflux at 90 °C for 4 h.After the reaction, recovered solvent and extracted with the equal volume of CHCl 3 and H 2 o.Evaporated water layer to dryness and dissolved in 1 mL of pyridine, mixed with 2-5 mg of L-cysteine methyl ester hydrochloride to react for 2 h at 60 °C.After completion, made it dry completely and added 200 μL of trimethylimidazosilane to react at 60 °C for 1 h.After the reaction, added 1 mL of water and extracted with an equal volume of cyclohexane.The organic layer was analyzed by GC [Agilent 6890 N with FID detector, and HP-5 capillary column (30 m × 0.25 mm × 0.25 μm)] (Wen et al. 2020).Standard D-glucose treated in the same way.