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Research Article
 

Isolation and Characterization of Flavanone Glycoside 4I,5, 7-Trihydroxy Flavanone Rhamnoglucose from Garcinia kola Seed



D.E. Okwu and F.N.I. Morah
 
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ABSTRACT

The ethanolic extract of Garcinia kola, Heckel (Guttiferae), which had previously been shown to have biological activity were studied. Preliminary phytochemical screening of the plants showed the presence of flavonoids, phenolic compounds, tannins and saponins. The ethanolic extract of Garcinia kola seeds resulted in the isolation and characterization of flavanone glycoside 4I, 5, 7-trihydroxyflavonone rhamnoglucose (that is naringin-7-rharmnoglucoseside) from its spectral data. IHNMR spin system analysis and acid hydrolysis were performed to characterize the higher order rhamnoglucosyl moiety comprising glucose and rhamnose linked to carbon 7 of the flavanone ring system of the isolate. It is concluded that 4I, 5, 7-trihydroxyflavanone rhamnoglucose may be a contributor to the antioxidants, anti-inflammatory, anti-microbial, anti-tumor and anti-hepatotoxic properties exhibited by Garcinia kola seed.

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  How to cite this article:

D.E. Okwu and F.N.I. Morah, 2007. Isolation and Characterization of Flavanone Glycoside 4I,5, 7-Trihydroxy Flavanone Rhamnoglucose from Garcinia kola Seed. Journal of Applied Sciences, 7: 306-309.

DOI: 10.3923/jas.2007.306.309

URL: https://scialert.net/abstract/?doi=jas.2007.306.309

INTRODUCTION

Garcinia kola Heckel (Bitter kola), belongs to the family Guttiferae found mainly in the tropical rain forest region of Central and West Africa (Keay, 1989; Uko et al., 2001). In addition to its use as alternative to hops in the brewing industry (Ogu and Agu, 1995; Aniche and Uwakwe, 1990) and in the treatment of cirrhosis and hepatitis in phytomedicine (Okwu, 2005, 2003; Nwankwo et al., 2000), Garcinia kola seed have been investigated for its ability to suppressed colic disorders, cure head or chest colds (Okwu, 2005; Iwu, 1986). The anticancer and chemo-preventive properties of the plant have been studied (Farombi et al., 2005, Akintonwa and Essien, 1990).

The main flavonoids content isolated from G. kola seed is kolaviron, a defatted ethanol extract from the seeds. Kolaviron is a mixture compounds comprising garcinia biflavonoids and kolaflavanone (Nwakwo et al., 2000; Iwu et al., 1990). It have been reported (Adaramoye et al., 2005; Farombi et al., 2005; Olaleye et al., 2000; Ibironke et al., 1997) that the flavonoids and phenolic compounds present in the plant are responsible for antioxidants, anti-inflammatory, anti-tumor, anti-hepatotoxic, anti-ulcer and anti-microbial properties exhibited by the plant.

This research describes the isolation and identification of new phytoconstituents from the seed of Garcinia kola.

MATERIALS AND METHODS

Sample collection: Mature seeds of Garcinia kola were purchased from Ariam market, Ikwuano Local Government Area of Abia State, Nigeria. On 15th July 1997. The plant materials (leaves, flowers, fruits and seeds) were identified and authenticated by Dr. A Nmeregini of Taxonomy Section, Forestry Department, Michael Okpara University of Agriculture Umudike, Nigeria. The voucher specimens were deposited in Forestry Department Herbarium of Michael Okpara University of Agriculture Umudike, Nigeria.

Treatment of plant materials: Plant materials were treated and analyzed at the Chemistry laboratory, Michael Okpara University of Agriculture Umudike. Mature seeds of Garcinia kola (1 kg) were dried on the laboratory bench for 10 days. The dry sample was milled and ground into powder (450 kg) using Thomas Wiley Machine. The powdered plant materials is dried and stored in airtight bottles for chemical analysis. The powdered plant sample (100 kg) was packed into a Soxhlet apparatus (2 L) and extracted exhaustively with 1000 mL ethanol for 24 h. The ethanolic extract was concentrated using a rotary evaporator at 45°C and in a hot air circulatory oven afforded a dark brown oil (16 kg).

Thin layer chromatography (chloroform: methanol 7:3) iodine vapour gave one band Rf 0.98 (blue). The resultant EtOH extract was applied to a silica gel column and eluted with acetone: ethanol (7:3). The eluted sample was re-chromatographed through the column with 50% chloroform in diethyl ether afforded a brown crystal (7 mg). This was re-crystallized from hexane to afford compound 1, yellow solid (6.1 mg), melting point 262-264°C, UV (MeOH) max 290 nm, IR Vmax 1641 (C = C) aromatic, 1726 (C = O) ether, 2859 (OH-phenol). IHNMR CDCl3, TMS δ-scale ppm) 7.39 2 Hd (H6I and H2I) 6.0 bs (OH), 6.85 2 H b poorly resolved (H6 and H8), 5.20 1Hm (H2), 3.0-4.2 unresolved (Sugar OH and CH2 protons), 5.91 (1H brs H-Rha-1), 5.31 (1H brd H-6), 4.96 (1Hd H-GLC-1), 3.92 (1Hm) 1.05 (3 Hs-H-Rha).

Acid hydrolysis of 1: Compound 1 (5.0 mg) was refluxed with 1M HCl/dioxane 1:1 V/V 2 mL) on a water bath for 6 h. The reaction mixture was evaporated to dryness. The dry reaction mixture was partitioned four times between CHCl3 and H2O. The CHCl3 layer was concentrated and subjected to silica gel column chromatography CHCl/EtOAC to provide compound 2 (3 mg), white amorphous powder, 1 R (KBr) V max 3416, 2933, 1456, 1068, 1050, 190 cm-1, IHNMR (pyridine-d2) 5.19 (1Hbrs H-Rha-1), 5.31 (1Hbr d H-6), 4.96 (1Hd H-GLC-1, 4.77 (1Hd-H-GLC-1), 3.92 (1Hm H-3) 1.72 (3Hd H-Rha-6) 1.08 (3Hd) 1.05 (3Hs-H rha).

Acid hydrolysis of 2: Compound 2 was subjected to acid hydrolysis as described for 1 to give D. glucose acid L. rhamnose as sugar moieties shown by sugar analysis with Benedicts reagent (Moore et al., 1982).

RESULTS AND DISCUSSION

Garcinia kola seed afforded a compound Mp 262-264°C, the compound was identified as flavonone rhamnose glycoside (naringin-7-rhamnoglucoside (i.e., 4I, 57-trihydroxyflavonone rhamnoglucoside) 1.

This identification is based on the physical data, Mp, UV, IR and IHNMR spectroscopy, which is in accord with literature data (Harborne et al., 1975; Alias and Linden, 1999).

The IHNMR spectrum of 1 showed a methyl signal at δ1.085. Acid hydrolysis of 1 produced the rahmnoglucosyl moiety 2 comprising glucose and rhamnose linked to Carbon 7 of the flavonone ring system and 41, 5, 7-trihydroxyflavanone compound 3. Compound 3 is non bitter yellow compound known as naringenin (Alias and Linden, 1999). Acid hydrolysis of 2 with 1 M HCl gave L-rhamnose and D-glucose as sugar residues.

The conjugation of the electrons of the heterocyclic ring within the aromatic system may be responsible for the yellow colour of the flavonoid compound isolated from the Garcinia kola seed.

Image for - Isolation and Characterization of Flavanone Glycoside 4I,5, 7-Trihydroxy Flavanone Rhamnoglucose from Garcinia kola Seed

The presence of this phenolic compound in Garcinia kola indicates that this plant may be anti-microbial agent since phenols and phenolic compounds are extensively used in disinfections and remain the standard with which other bactericides are compared (Okwu, 2005, 2003). Phenolic form a large group of naturally occurring diverse and widespread compounds. They are characterized by the presence of an aromatic ring with one or more hydroxyl groups. These phenolic compounds in Garcinia seed may be responsible for the therapeutic, antiseptic, antifungal or bactericides properties of the plants (Okwu, 2005).

This agreed with the findings of Akoachere et al., (2002) who reported that G. kola seed extracts exhibited inhibition on Streptococcus pyogenes, Streptococcus pneumoniae and Hemophilis influenza. The observed inhibiting role on these microorganism explains the reason behind the utilization of G. kola extract in traditional medicine as cough suppressant, anti-tumor agent, wound healing activity and an aphrodisiac (Akoachere et al., 2002; Okwu, 2003, 2005). Flavonoids are phenolic potent, water-soluble super anti-oxidant and free radical scavengers which prevent oxidative cell damage, have strong anti-cancer activity and anti-inflammatory properties (Olaleye et al., 2000). This plant, has been used in phytomedicine to protect and regenerate liver cells and in the treatment of cirrhosis and hepatitis (Okwu, 2005; Nwankwo et al., 2000). These phytochemicals isolated are responsible for the marked medicinal properties of the plant. Compound 1 have earlier been isolated from grape fruits, lemons, hops and oranges and is responsible for the bitter taste of these fruits (Alias and Linden, 1999). Flavanone is partly responsible for the bitter principle or astringent flavour of the Garcinia seed. Acid hydrolysis with 1 M HCl removes the rhamnoglucosyl moiety of compound 1 and also its bitter properties.

With naringin-7-rhamnoglucoside and the anti-microbial activity of Garcinia kola seeds, it will serve as a good substitute for the brewing of larger beer. The isolation and characterization of this bitter principle lend credence to the common use of Garcinia kola as an antibacterial and antifungal drug. This supports its utilization in phytomedicine in Nigeria.

ACKNOWLEDGMENT

Special gratitude goes to the Senate of Michael Okpara University of Agriculture Umudike Nigeria for a grant given to Dr. D.E. Okwu in support of this work. We are also grateful to Dr. Nmeregini of the Forestry Department, Michael Okpara University of Agriculture Umudike Nigeria, who authenticated the samples.

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