Antioxidant Activities of Flavonoid Aglycones from Kenyan Gardenia ternifolia Schum and Thonn

Awas E, Omosa LK, Midiwo JO, Ndakala A, Mwaniki J. "Antioxidant Activities of Flavonoid Aglycones from Kenyan Gardenia ternifolia Schum and Thonn." IOSR Journal of Pharmacy and Biological Sciences (IOSR-JPBS). 2016;11(3):136-141.


Phytochemical investigation of surface exudates of the leaves of Gardenia ternifolia resulted to
characterization of four flavonoids; 3,5,3′-trihydroxy-7,4′-dimethoxyflavone (1), 5,7-trihydroxy-4′-
methoxyflavone (2), 5,7-dihydroxy-3,4′-dimethoxyflavone (3), 5,4′-dihydroxy-7-methoxyflavanone (4) and two
tritepenoids; β-sitosterol (6) and stigmasterol (7). Compound 1 exhibited the highest antioxidant activity with
IC50 = 40.3± 1.55 μΜ. The rest of the flavonoids showed minimal activities with IC50 values of 75.5±1.75,
89±0.22, 94±0.11 μΜ for 2-4, respectively. The antioxidant activities of 1 was substantially lower than the
standard, quercetin (IC50 = 20.1±1.34 M). Methoxylation of quercetin at 7 and 4′-position in 1 substantially
reduced antioxidant potential. Lack of oxygenation at 3′ position, as observed for kaempferol derivatives was
responsible for further reduction in the radical scavenging potential as observed for 2 and 3. Furthermore,
methylation of 3-OH position in kaempferol derivatives further reduced the antioxidant activities as exhibited by
3 with an oxygenation pattern similar to 2 except for the methylation at 3-position. The results of this study are
consistent with previous findings that revealed that flavonols, exhibited better anti-oxidant activities as
compared to 3-methoxyflavones. Acetylation of 3 at the 5 and 7 positions resulting to 3,4′dimethoxy-5,7-
diacetylflavone (5), substantially reduced the activity of this compound. The triterpenoids exhibited were
inactive as expected.
Keywords: Antioxidant activities, Gardenia ternifolia, surface exudates

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