Chemical constituents and antioxidant activities of the fruits extracts of Piper capense
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