Luteolin and Kaempferol From Cassia Alata

LUTEOLIN AND KAEMPFEROL FROM CASSIA ALATA, ANTIMICROBIAL AND ANTIOXIDANT ACTIVITY OF ITS METHANOLIC EXTRACTS

ANEELA WAHAB, TAHIRA, SABIRA BEGUM, ANJUM AYUB, IFFAT MAHMOOD, TALAT MAHMOOD, AQEEL AHMAD AND NIDA FAYYAZ

Abstract

Cassia alata also known as candlebush is a medicinally important plant. In the present investigation we are reporting the isolation and structure elucidation of two flavonoids kaempferol (1) and luteolin (2) isolated from methanolic extract of its beans through bioassay guided fractionation. The structure of isolated compounds were characterized by spectroscopic techniques such as EIMS, ¹H-NMR and ¹³C-NMR. In this article we are also presenting the antibacterial, antifungal and antioxidant activity of the methanolic extract of its leaves (CA-L), stem (CA-S) and beans (CA-BN). All the extracts showed remarkable antibacterial and weak antioxidant activity whereas moderate antifungal activity was only found in stem (CA-S) and beans (CA-BN) extracts.

Introduction

Cassia alata (Synonym; Senna alata) belonging to the family Leguminosae and subfamily of Fabaceae, commonly known as seven golden candlesticks, and ringworm senna (Quattrocchi U., F.L.S., 2012). This plant is native to the West Indies, tropical America, found wild almost throughout India and Pakistan (Khare C.P., 2007). C. alata with golden blooms is a summer bloomer and a striking spring that last for several weeks but prefer cooler month for flowering (Ray A.B., et al., 2010, Krishnan M. K. S., 1992). This shrub may grow up to 3 meters tall with irregular, angled, glabrous branches. Flowers have bright yellow colour. It has long, membranous, dehiscent pods with 25 or more seeds per pod (Ross I.A., 2003, Bhattacharjee S.K., 2004).

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Cassia alata is widely used as traditional medicine in India and Southeast Asia ( Reezal I., et al., 2002 ). This plant is reported to possess insecticidal, anti-inflammatory, hydragogue, sudorific, diuretic, pesticidal properties. Fresh leaves juice is used for ring worm, snakebite, scorpion bite, skin diseases, impetigo, syphilis sores, itching, mycosis (washerman’s itch), herpes and eczema. Roots, leaves and flowers of this plant possess many biological properties such as antibacterial, antifungal, anti-inflammatory, antitumor, expectorant and also useful in urinary tract problems (Quattrocchi U., F.L.S., 2012), asthma, bronchitis and constipation (Joshi S.G., 2000). The ethyl acetate extract of C. alata leaves possess hypoglycaemic activity (Ray A.B., et al, 2010). This plant also has hepatoprotective property. The main constituents of C.alata are flavonoids, alkaloids, anthraquinone derivatives, tannins, sterols and triterpenes (Neharkar V.S., Gaikward K.G., 2011). The present paper describe the isolation and characterization of kaempferol (1) and luteolin (2). Herein we are also reporting the antimicrobial and antioxidant activities of the methanolic extract of leaves, stem and beans of this plant. All the extracts showed significant antibacterial (Table 2) and weak antioxidant activity (Table 4). Antifungal activity (Table 3) was only observed in the extract of stem and beans.

Experimental

Materials and Methods

General:

Silica gel PF₂₅₄ (Merk) was used for vacuum liquid chromatography (VLC). Thin layer chromatography (TLC) was performed on pre-coated silica gel F₂₅₄ (Merck). Gel permeation chromatography was performed on sephadex LH-20 (Pharmcia). The EIMS (electron impact mass spectrometery) were scanned on Jeol-JMS HX-110 mass spectrormeter. The ¹H and ¹³C-NMR (Nuclear Magnetic Resonance) spectra were recorded on a Bruker spectrometer operating at 300 and 75 MHz respectively. The chemical shift values are reported in  (ppm) relative to SiMe₄ (Tetra methyl silane) as an internal standard. The coupling constant (J) is given in Hz.

Plant Material:

The Cassia alata was collected from Karachi (Sindh) and identified by Mr. Ghulam Rasool. A voucher specimen (86464) has been deposited in the herbarium at Department of Botany, Faculty of Science University of Karachi, Sindh Pakistan.

Extraction and Isolation:

The air dried leaves (7 kg), stem (5 kg) and beans (5 kg) of Cassia alata were extracted repeatedly with methanol at room temperature. The solvent was evaporated under vacuum to give 2 kg crude extract of leaves (CA-L), 3 kg crude extract of stem (CA-S) and 750 g crude extract of beans (CA-BN). The dark greenish brown gummy crude extract of beans (CA-BN) was partitioned with ethyl acetate (EtOAc), water (discard) and n-butanol fractions. Each fraction was concentrated in vacuum to have 15 g EtOAc and 15 g n-butanol soluble fractions. The EtOAc soluble fraction was further partitioned with n-hexane to obtained n-hexane soluble fraction and n-hexane insoluble fraction. The n-hexane soluble fraction (14 g) was subjected to vacuum liquid chromatography (VLC) (n-hexane: n-hexane: EtOAc in order of increasing polarity) which furnished 22 fractions (Fr-1-Fr-22). The Fr-15 was subjected to reverse-phase column chromatography using sephadex column LH-20 (CHCl₃;CHCl_3:MeOH in order of increasing polarity) which yielded 12 fractions (Fr-15-1-Fr-15-12). The Fr-15-9 was further subjected to reverse phase column chromatography using sephadex column LH-20 (n-hexane:CHCl₃:MeOH in order of increasing polarity) furnished 18 fractions (Fr-15-9-1-Fr-15-9-18). The Fr-15-9-10 eluted with n-hexane:CHCl₃:MeOH (0.5:3:1.5) gave yellow amorphous powder which showed single spot on TLC using CHCl₃: MeOH (9.2:0.8) as a solvent system was identified as kaempferol (1) (37 mg). The Fr-15-9-9 was further subjected to reverse-phase column chromatography using sephadex column LH-20 (n-hexane:CHCl₃:MeOH in order of increasing polarity) which yielded 13 fractions (Fr-15-9-9-1 to Fr-15-9-9-13). The Fr-15-9-9-3 eluted with n-hexane:CHCl₃:MeOH (0.5:3:1.5) showed single spot on TLC (CHCl₃:MeOH, 9.2:0.8) appeared as yellowish powder and was identified as luteolin (2) (27 mg).

Biological assay:

Screening of antibacterial activity:

The disc diffusion method (Bauer et al, 1966) was used to determine the antibacterial activity of methanolic extracts. 100 mg/ml of stock solution was prepared by dissolving extracts in DMSO. Sterile filter discs containing 10 l of stock solution were used for screening. The Mueller Hinton agar (Oxoid) plates were seeded with 24 hours old culture grown in Mueller Hinton broth (Oxoid). The prepared discs were placed onto the surfaces at different positions and plates were incubated at 37C for 24 hours. Results were recorded by measuring the zone of inhibitions in mm. Gentamicin was used as a standard.

Screening of antifungal activity:

Antifungal activity was also determined by disc diffusion method (Bauer et al, 1966) as above. Briefly, a small amount of culture was transferred to 2-3 ml distilled water or normal saline in a screw capped tube with few glass beads (1 mm in diameter) and vortexes for 5-10 minutes to make a homogeneous suspension of fungal culture. Sabouraud dextrose agar (SDA) plates were seeded with this suspension. Sterile filter discs containing 10 l of stock solution were placed onto the surfaces at different positions. Plates were incubated at room temperature for 1 week. Results were recorded by measuring the zone of inhibitions in mm. Gresiofulvin was used as a standard.

Determination of minimum inhibitory concentration (MIC):

MIC of methanolic extracts were determined by the disc diffusion method ( Bauer et al, 1966).

Sterile discs containing different concentrations of samples varying from 0.98 to 1000 g per disc were prepared. The MIC of those extracts showing maximum zone of inhibition against microorganism were calculated ( Table 2 ).

Antioxidant activity:

Antioxidant activity was determined by using the method described by Lee et al. (1998). 1,1-diphenyl-2-picrylhydrazyl (DPPH) was prepared in ethanol (300 µM). 10 µL of each extract and 90 μL solution of stable radical, 1,1-diphenyl-2-picrylhydrazyl (DPPH) was added in 96 – well micro titer plates and incubated at 37º C for 30 minutes. Absorbance was measured at 515 nm by using a spectrophotometer. Percent inhibition of radicals by treatment of test sample was determined by comparison with a DMSO treated control group.

% Inhibition = (absorbance of the control-absorbance of the test sample) x 100

Absorbance of the control

Ascorbic acid was used as standard control. The EC₅₀ value calculated denotes the concentration (in ug/ml) of sample required to scavenge 50% of DPPH

Characterization of Kaempferol (1)

Yellow amorphous powder. ¹H-NMR  (300 MHz, CD₃OD): 8.09 (2H, d, J = 8.7 Hz, H-2’, 6’), 6.91 (2H, d, J = 8.7 Hz, H-3’, 5’), 6.43 (1H, d, J = 1.8 Hz, H-8), 6.19 (1H, d, J = 1.8 Hz, H-6). EIMS m/z: 286 [M]⁺. ¹³C-NMR (see Table 1). All data were identical with that of reported in literature (Hadizadeh F., et al, 2003, Gangwal A., et al, 2010).

Characterization of Luteolin (2)

Yellow amorphous powder. ¹H- NMR  (300 MHz, CD₃OD): 7.39 (1H, dd, J = 9.0, 1.8 Hz, H-6’) ,7.36 (1H, d, J = 1.8 Hz, H-2’), 6.88 (1H, d, J = 9.0, Hz, H-5’), 6.53 (1H, s, H-3), 6.43 (1H, d, J = 1.8 Hz, H-8), 6.19 (1H, d, J = 1.8 Hz, H-6). EIMS m/z: 286 [M]⁺. ¹³C-NMR (see Table 1). All data were identical with that of reported in literature (Saeidnia S., et al, 2009).

Results and discussion:

The phytochemical investigation of the methanolic extracts of Cassia alata beans resulted in the isolation of kaempferol (1) and luteolin (2). Compound (1) showed molecular ion peak at m/z 286 having molecular formula C₁₅H₁₀O₆. Its ¹H-NMR spectrum showed the characterstic peak of H-2^’ and 6^’ as a doublet at with ortho coupling of 8.7 Hz whereas H-3^’ and 5^’ with similar ortho coupling appeared at 6.91 as a doublet.¹H-NMR spectrum of 1 further displayed signals of aromatic protons as a doublet at 6.19 (H-6) and at  6.43 (H-8) showing meta coupling of 1.8 Hz.

The EIMS spectrum of compound (2) is similar to (1) having same molecular mass (m/z 286) and formula (C₁₅H₁₀O₆). In the ¹H-NMR spectrum of 2 characterstic peak of H-3 appeared at 6.53 as a singlet. Other important signals observed at 6.88 (d, J = 9.0, Hz, H-5^’), 7.36 (d, J = 1.8 Hz, H-2^’) and 7.39 (dd, J = 9.0, 1.8 Hz, H-6^’). The aromatic protons H-6 and H-8 showed same and J value as in compound 1. The ¹³C-NMR spectrum (Table 1) of both compounds 1 and 2 displayed signals of nine quaternary and six methine carbons . All the ¹³C assignments are in agreement with the reported data (Gangwal A., et al, 2010, Saeidnia S., et al, 2009).

The results of antibacterial activity indicated that all the methanolic extracts of C. alata (CA-L, CA-S and CA-BN) have potential to kill various pathogenic gram+ve and gram-ve bacteria (Table 2), whereas good antifungal activity was observed in CA-S and CA-BN extracts against Fusarium specie (Table 3). All the extracts (CA-L, CA-S and CA-BN) showed less than 50% inhibition of DPPH radicals in antioxidant activity (Table 4).

CONCLUSION:

The known flavonoids kaemferol (1) and luteolin (2) were isolated from the methanolic extracts of C. alata beans. The structure of the isolated compounds were elucidated by various spectroscopic techniques. Pharmacological investigations have indicated that all the extracts (CA-L, CA-S and CA-BN) of this plant possess significant antimicrobial and weak antioxidant activity.

References:

Bauer, A.W., Kirby, W.M.M., Sherris, J.C., & Turck, M. (1966). Antibiotic susceptibility testing by a standardized single disk method. American Journal of Clinical Pathology, 45, 493–496.

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Table 1. C¹³-NMR spectral data of kaempferol (1) and luteolin (2) in CD₃OD (ppm) at

75 MHz

Table 2. Antibacterial activity of different extracts of Cassia alata (zone of inhibition

in mm)

CA-L= Cassia alata Leaves, CA-S = Cassia alata Stem, CA-BN = Cassia alata Beans.

Table 3. In Vitro Antifungal activity (zone of inhibition in mm)

Table 4. Antioxidant activity of Methanolic extracts of C.alata