Flavonoids from Tithonia diversifolia and their Antioxidant and Antibacterial Activity
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FLAVONOIDS FROM Tithonia diversifolia AND THEIR ANTIOXIDANT AND ANTIBACTERIAL ACTIVITY
Bongani Sicelo Dlamini,1 Chiy-Rong Chen,2 Douglas J. H. Shyu,3 and Chi-I Chang3,4*
Tithonia diversifolia (Asteraceae) is a herb conventionally used for the treatment of malaria, wounds, and other illness [1]. Recent phytochemical studies highlighted the biological properties of T. diversifolia such as antioxidant, antimalarial, antidiabetic, antibacterial, and anti-hyperglycemic activities [2–6]. The traditional usage and pharmacological properties of the genus Tithonia led to the investigation of the bioactive constituents of T. diversifolia. In this research, four flavonoids were isolated from the genus Tithonia for the first time and identified as pachypodol (1), 3,7-dimethylquercetin (2), retusin (3), and chrysosplenetin (4). The flavonoids are reported to possess antibacterial, antiviral, anti-inflammatory, anticancer, and antioxidant activities with the potential of treating several ailments [7]. The flavonoids can be an alternative medicine for the cure of infections, considering the emerging resistance of microorganisms to therapeutic agents. Hence, in this study, we investigated the antibacterial and antioxidant activity of the flavonoids from T. diversifolia stems. Compounds 1, 2, and 4 displayed antiradical activity, while compound 3 showed no activity (Table 1), which is associated with the absence of the para positioned hydroxyl functional group in the B-ring, whereas compounds 1, 2, and 4 possess the hydroxyl group. The results showed that the hydroxyl functional groups and their relative positions have a substantial influence on the antiradical properties of the flavonoids, which explains the radical scavenging activity of the compounds. The compounds with methoxyl group at C-3′ instead of the hydroxyl group showed high scavenging activity against the superoxide radical as compared with the DPPH radical. We observed that the methylation of hydroxyl group at C-3′ in flavonoids decreased their DPPH radical scavenging effect and increased their superoxide radical scavenging activity. Compound 2 displayed the highest DPPH radical scavenging activity with the IC50 value of 371 μM, followed by compounds 4 and 1 with the IC50 values of 473 and 1084 μM, respectively, while compound 3 was inactive. Compounds 1 and 4 demonstrated significant superoxide anion radical scavenging effect with IC50 values 573.7 and 787.5 μM, respectively, when compared with that of BHT (1136.4 μM), which is in agreement with the literature [8, 9], followed by compound 2 with the IC50 value of 2720.2 μM, while compound 3 was inactive. Even though the DPPH radical scavenging effects of the compounds were not comparable with that of BHT, the relationship between their structure and antioxidant activities is worth consideration. The antibacterial properties of the compounds were classified as significant with MIC below 50 μM, moderate (50–500 μM), and low with MIC values above 500 μM [10]. The compounds showed a low bacteriostatic effect against ba
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