Phenolic compounds from the leaves of Ricinus communis Linn

Use your smartphone to scan this QR code and download this article ABSTRACT Introduction: Ricinus communis Linn. (Castor oil plant) is a monotypic species of Ricinus genus (Euphorbiaceae) and widely distributed in all tropical countries. Phytochemical data of this plant are scarce. As part of ongoing research on a survey of Vietnamese medicinal plants, the investigation of this plant was performed. The isolation and structural determination of five phenolic compounds isolated from the leaves of R. communis Linn. growing in Binh Phuoc province were addressed. Method: The dried power of R. communis Linn. leaves was macerated in ethanol to afford the crude extract, which was then separated by liquid-liquid extraction with n-hexane, chloroform, and ethyl acetate, respectively to obtain the corresponding extracts. These extracts were applied to multiple silica gel column chromatography and thin-layer chromatography to yield five compounds. Their chemical structures were determined by spectroscopic methods and by comparison of NMR data with literature values. Antioxidant evaluation of 1 was carried out using 1,1diphenyl-2-picrylhydrazyl radical (DPPH) free radical scavenging assay. Results: Five phenolic compounds, including one coumarinolignan cleomiscosin A (1), two flavonol glycosides kaempferol3-O-β -D-glucopyranoside (2) and kaempferol-3-O-β -D-xylopyranoside (3), and two aromatic acids gallic acid (4) and vanillic acid (5) were identified. Conclusion: Compound 1 was determined for the first time in Ricinus genus and exhibited weak DPPH radical scavenging activity with an SC50 value of 403.23 μg/mL.


INTRODUCTION
Ricinus communis Linn. is a single species belonging to the spurge family (Euphorbiaceae) and widespread throughout tropical countries, including South Africa, India, Brazil, and Russia 1,2 . This castor oil plant has been used for the treatment of inflammation and liver disorders in India, reported having hepatoprotective, laxative, antidiabetic, and antifertility activities in Tunisia 3 . Its leaves have traditional applications for headache, inflammatories, and antibacterials against Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus 1,4 . Previous studies on the leaves of R. communis determined the presence of alkaloids, flavonoids, phenolic compounds, triterpenoids, and steroids [5][6][7] . Herein, the isolation and structural elucidation of five phenolic compounds, including one coumarinolignan cleomiscosin A (1), two flavonol glycosides kaempferol-3-Oβ -D-glucopyranoside (2) and kaempferol-3-O-β -Dxylopyranoside (3), and two aromatic acids gallic acid (4) and vanillic acid (5) from the leaves of R. communis Linn. collected in Bu Dang district, Binh Phuoc province, Vietnam, were reported.

General experimental procedures
The HR-ESI-MS and APCI-MS spectra were carried on a Bruker micrOTOF Q-II and LC-MSD-Trap-SL. The NMR spectra were recorded on a Bruker Avance 500 (500 MHz for 1 H-NMR and 125 MHz for 13 C-NMR) spectrometer. Column chromatography was applied on silica gel 60 (Merck, 40-63 µm). TLC was conducted on precoated silica gel 60 F 254 (Merck Millipore, Billerica, Massachusetts, USA), and spots were visualized by spraying with 10% H 2 SO 4 solution followed by heating.

Extraction and isolation
The R. communis leaves were washed, dried, and ground into powder (15.0 kg), which was then extracted with ethanol (10 x 5 L) by the maceration method at room temperature. The filtrated solution was evaporated under reduced pressure to yield the crude ethanol extract (1.15 kg). This crude extract dissolved in solvent systems of methanol: water (1:9, v/v) was partitioned against n-hexane, chloroform, and ethyl acetate, respectively. The obtained solutions were evaporated to afford the corresponding residues: n-hexane (300.0 g), chloroform (220.0 g), and ethyl acetate (210.0 g) extracts.

DPPH scavenging assay
The assay was carried out following the method reported previously 10 . Trolox was used as a positive control. Compound 1 was analyzed in triplicate, and results are given as averages ± SD.

DISCUSSION
Cleomiscosin A (1), found for the first time in Aesculus turbinate 13 showed various biological activities, i.e. anti-inflammatory 14 , antihepatotoxicity 15 , and antitumor activities 16 . Derivatives of this compound were prepared to evaluate the structure-activity relationship 14 . To the best of our knowledge, this is the first isolation of 1 from Ricinus genus. Astragalin (2), a potential therapeutic compound, was isolated from many higher plants, Cuscuta chinensis or Cassia alata 13 . This compound was found in the roots of R.communis which was considered to possess mast cell stabilizing, antianaphylactic activity and antiasthmatic activity 17

CONFLICTS OF INTEREST
The authors declare no competing financial interest.

AUTHOR CONTRIBUTION
Pham N.K.T has contributed in conducting experiments, acquisition of data, and interpretation of data. Tran T.T.L., Dinh V.S, Nguyen V.T, Dang V.S., Nguyen T.Q.T., Nguyen D.X.K, Nguyen T.P. interpreted NMR and MS data as well as searched the bibliography. Huynh B.L.C and Duong T.H. gave final approval of the manuscript to be submitted.