Abstract
The fruits of P. capense from Ethiopia were hydro-distilled with Clevenger apparatus to furnish 2.6-2.8% yellowish oil which was analyzed with GC–MS. Results of the GC-MS analysis revealed the presence of twenty one components with the major ones are β-caryophyllene (5%), g-muurolene (7.22%), germacrene D (9.30%), dihydroxy-isocalamendiol (11.6%), and cis-muurola-3,5-diene (15.6%). The fruits were also successively extracted with n -hexane and EtOAc to give 1.3% and 2.3% yield on dry weight basis, respectively. The EtOAc extract was screened for the presence of secondary metabolites which showed the presence of alkaloids, phenols, steroids, flavonoids, saponins and terpenoids while tannin was not detected. The EtOAc extract after silica gel column chromatography resulted in the isolation of 5-hydroxy-7,4’-dimethoxyflavone. The DPPH radical scavenging activity of the EtOAc extract, essential oil and 5-hydroxy-7,4’-dimethoxyflavone were evaluated and found to inhibit DPPH radical by 78%, 70% and 84% at 100 µg mL -1 , respectively. Likewise, the EtOAc extract, essential oil and 5-hydroxy-7,4’-dimethoxyflavone inhibited peroxidation of lipid by 74, 64 and 80%, respectively. The results are significant compared to ascorbic acid used as positive control suggesting the use of the fruit of P. capense as a natural antioxidant. KEY WORDS : Piper capense , DPPH, Ferric thiocyanate, 5-hydroxy-7,4’-dimethoxyflavone Bull. Chem. Soc. Ethiop. 2018 , 32(1), 167-174 DOI: https://dx.doi.org/10.4314/bcse.v32i1.16
Highlights
Piper capense is an endemic medicinal plant of east Africa found in the genus Piper and family Piperaceae [1]
The antioxidant activity of the ethyl acetate extract, essential oil and compound 1 (Table 1) of the fruits of P. capense were measured by bleaching of the purple-colored solution of 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) at four different concentrations (100, 50, 25 and 12.5 μg mL-1)
This is most likely due to its strong ability of donating an electron and phenolic hydrogen to DPPH radical, which was visualized by immediate discoloration of the purple DPPH solution to yellow compared to the essential oil and the ethyl acetate extract of the fruits of P. capense
Summary
Piper capense is an endemic medicinal plant of east Africa found in the genus Piper and family Piperaceae [1]. The ethyl acetate extract (4 g) was fractionated over silica gel column chromatography with n-hexane:EtOAc of increasing polarities as eluent to afford thirty five fractions (each 50 mL). The ethyl acetate extract of the fruits of P. capense were screened for the presence of secondary metabolites including flavonoids, phenols, terpenoids, alkaloids, saponins, steroids and tannins following previously developed standard procedure [9].
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