Alkaloids and Iridoids From the Aerial Parts of Rauvolfia cambodiana Pierre ex Pit. and Their Acetylcholinesterase Inhibitory Activity

Abstract

Objective: Rauvolfia cambodiana has been used as a Vietnamese folk medicine to treat high blood pressure and for sedation and memory loss diseases. However, to date, there have been few studies on the chemical constituents and biological activity of this medicinal plant. This study aimed to find the chemical constituents of R cambodiana and evaluate their enhancement memory properties. Methods: The aerial parts of R cambodiana were powdered and ultrasonically extracted with methanol. The methanol extract was suspended in water and successively partitioned with dichloromethane and ethyl acetate to give dichloromethane, ethyl acetate, and water-soluble extracts. Each extract was fractionated and purified by column and HPLC chromatographic methods. The chemical structures of the isolated compounds were elucidated by analysis of HRESIMS, 1D and 2D NMR spectra, and experimental and TD-DFT calculated ECD spectra. The enhancement memory property of the compounds was evaluated by their in vitro acetylcholinesterase inhibitory activity. Results: Five alkaloids (1-5) and 2 iridoids (6 and 7), including one new one named rauvolcambonine (1), and 6 known compounds, perakine (2), ajmaline (3), 10-hydroxy-16- epi-affinine (4), sitsirikine (5), loganic acid (6), and secoxyloganin (7) were isolated and identified from the aerial parts of R cambodiana. Compounds 4 and 5 significantly showed acetylcholinesterase inhibitory effects in vitro with IC50 values of 30.1 ± 1.4 µM and 65.5 ± 3.3 µM, respectively. The other compounds inhibited acetylcholinesterase with IC50 values ranging from 111.0 ± 6.0 µM to 197.6 ± 19.8 µM. Conclusion: One new (1) and 3 other compounds (2, 4-7) were recorded from R cambodiana for the first time. The NMR spectroscopic data of compound 4 are reported herein for the first time. Our study preliminarily revealed that the vobasenal framework type alkaloids could be active ingredients of Rauvolfia species and responsibility for the enhancement memory property of these plants.