Antioxidant constituents of Nymphaea caerulea flowers

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https://doi.org/10.1016/j.phytochem.2008.04.009Get rights and content

Abstract

As part of an ongoing search for antioxidants from medicinal plants, 20 constituents were isolated from the Nymphaea caerulea flowers, including two 2S,3S,4S-trihydroxypentanoic acid (1), and myricetin 3-O-(3′′-O-acetyl)-α-l-rhamnoside (2), along with the known myricetin 3-O-α-l-rhamnoside (3), myricetin 3-O-β-d-glucoside (4), quercetin 3-O-(3′′-O-acetyl)-α-l-rhamnoside (5), quercetin 3-O-α-l-rhamnoside (6), quercetin 3-O-β-d-glucoside (7), kaempferol 3-O-(3′′-O-acetyl)-α-l-rhamnoside (8), kaempferol 3-O-β-d-glucoside (9), naringenin (10), (S)-naringenin 5-O-β-d-glucoside (11), isosalipurposide (12), β-sitosterol (13), β-sitosterol palmitate (14), 24-methylenecholesterol palmitate (15), 4α-methyl-5α-ergosta-7,24(28)-diene-3β,4β-diol (16), ethyl gallate (17), gallic acid (18), p-coumaric acid (19), and 4-methoxybenzoic acid (20). The structures were determined by spectroscopic means. Compounds were tested for antioxidant activity and nine compounds 2–7, 11, 12 and 18 were considered active with IC50 of 1.16, 4.1, 0.75, 1.7, 1.0, 0.34, 11.0, 1.7 and 0.95 μg/ml, respectively, while 1 was marginally active (IC50 > 31.25 μg/ml). The most promising activity was found in the EtOAc fraction (IC50 0.2 μg/ml). This can be attributed to the synergistic effect of the compounds present in it.

Graphical abstract

Twenty constituents were isolated from the Nymphaea caerulea flowers, including 2S,3S,4S-trihydroxypentanoic acid (1), and myricetin 3-O-(3′′-O-acetyl)-α-l-rhamnoside (2), along with known 18 compounds (3–20). Antioxidant activities of nine compounds 2–7, 11, 12 and 18 were observed with IC50 values of 1.16, 4.1, 0.75, 1.7, 1.0, 0.34, 11.0, 1.7 and 0.95 μg/ml, respectively, while 1 was marginally active (IC50 > 31.25 μg/ml). Promising activity of EtOAc fraction (IC50 0.2 μg/ml) could be attributed to the synergistic effect of the compounds present in it.
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Introduction

Nymphaea caerulea Savigny (Nymphaeaceae), is an aquatic perennial plant growing on the shores of lakes and rivers and known by the common names blue lotus, blue water lily and Egyptian lotus. In folk medicine, the plant is reported to be soothing with tranquilizing effects and is reputedly a detoxicant and aphrodisiac along with astringent, diuretic properties. It is used in Ayurvedic medicine for dyspepsia, enteritis, diarrhea, urinary problems, fevers and heart palpitations (Encyclopedia of Herbs and their uses, 1995). Previous work on the flowers of this species resulted in the isolation of seven flavonol glycosides (Fossen et al., 1999) and three acylated anthocyanins (Fossen and Andersen, 1999). This work is a continuation of phytochemical investigations of unexploited flora for new sources of potential antioxidants. A preliminary screening showed that an EtOH extract of this plant and subsequent CHCl3, EtOAc fractions displayed significant antioxidant activity without any associated cytotoxicity. It is well known that having a diet rich in antioxidants, such as herbs, vegetables, fruits, and grains can prevent various diseases caused by reactive oxygen species (ROS) (Halliwell, 1994). Hence, the aim of this study was to investigate the phytochemical constituents of this plant and to evaluate their antioxidant activities. This paper describes the isolation, structure elucidation and evaluation of the antioxidant activity of two new compounds, 2S,3S,4S-trihydroxypentanoic acid (5-deoxyribonic acid) (1), and myricetin 3-O-(3′′-O-acetyl)-α-l-rhamnoside (2) along with several known compounds that were first reported from this plant (4, 7–20) in addition to previously reported flavonol glycosides (3–6) (Fossen et al., 1999) from the flowers of N. caerulea.

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Section snippets

Results and discussion

Compound 1 was isolated as colorless, optically active, needles. Its molecular formula of C5H10O5 was determined by HRESIMS and indicated one degree of unsaturation. 13C NMR and DEPT-135 spectra showed the presence of five carbon signals, including one methyl (δC 18.3), three oxymethine groups (δC 75.7, 78.8 and 80.9) and one carboxyl (δC 176.6). The presence of a carboxyl group was further supported by a peak in the IR spectrum at 1757 cm−1, indicative of a monomeric saturated aliphatic acid (

Concluding remarks

This study discloses that the EtOAc fraction of N. caerulea flowers was found to be rich with the derivatives of food derived flavonoids such as flavonols, quercetin, kaempferol and myricetin that have reported antimutagenic and anticarcinogenic effects in vitro and in vivo (Hertog et al., 1992). According to Kuhnau (1976) 1 g of mixed flavonoids are necessary to provide pharmacologically significant concentration in body fluids and tissue (Kuhnau, 1976) and the lack of flavonoids in quantity in 

General methods

Optical rotations were determined with a AUTOPOL IV polarimeter. UV spectra were obtained on a VARIAN 50 BIO UV–Visible spectrophotometer and IR spectra were recorded on a JASCO 302-A spectrometer. The 1D and 2D NMR spectra were run on a Varian 400 Mercury plus NMR spectrometer. Chemical shifts are expressed in δ values relative to the deuterated solvent. Multiplicity determination (DEPT) and 2D NMR spectra (COSY, HMQC, HMBC) were performed with standard pulse programs. GC/MS analysis was

Acknowledgments

The authors thank Dr. Avula B. for providing mass spectroscopic data and Frank T. Wiggers and Dr. Zulfiqar Ali of the National Center for Natural Products Research for NMR Data. This work was supported in part by the United States Department of Agriculture, Agricultural Research Service, Specific Cooperative Agreement No. 58-6408-2-0009 and Grant Number P20RR021929 from the National Center for Research Resources.


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