相思樹枝條抽出物之抗氧化活性及抑制黃嘌呤氧化酶活性

Abstract

Acacia confusa Merr. is an indigenous tree species that grows in Taiwan. In this study, phytochemical characteristics and bioactivities of the A. confusa twig and branch extracts were investigated. Antioxidant activities were evaluated by DPPH radical scavenging and superoxide radical scavenging assays, lipid peroxidation assay, reducing power and metal chelating ability on ferrous ions assays, and trolox equivalent antioxidant capacity (TEAC) assay. Meanwhile, total phenolic contents, total proanthocyanidin contents and total flavonoids contents were also measured. Results demonstrated that the extracts of 5 cm-branch bark possessed the best antioxidant activities and highest phenolics contents among twig and branches, indicating that branches with larger diameters have better antioxidant activities and higher phenolic contents. Furthermore, the antioxidant activities of branch extracts are stronger in the bark than in the wood. Among all fractions, both EtOAc fractions of A. confusa twig extracts and 5 cm-branch bark extracts have the best activities. Thin layer chromatography (TLC), column chromatography (CC), and high performance liquid chromatography (HPLC) were further employed to separate active phytochemicals and then chemical structures were identified using mass spectroscopy and nucleus magnetic resonance spectroscopy (NMR). Three catechins and one flavonoid were isolated from EtOAc fraction of 5 cm-branch bark extracts, including catechin, catechin-3-O-α-rhamnopyranoside, epi-catechin, and quercetin-3-O-α- rhamnopyranoside. Five flavonoids were isolated from EtOAc fraction of twig extracts, including myricetin-3-O-β-glucopyranoside, myricetin-3-O-α-rhamnopyranoside, quercetin-3-O-α-rhamnopyranoside, myricetin -3-O-(2’’-O-galloyl)-α-rhamnopyranoside, and luteolin. Results showed the constituents are significantly different between twig and branch extracts. Catechins are the major compounds in 5 cm-branch bark extracts, while flavonoid glycosides are the majority in twig extracts. Despite both branch and twig extracts showed no significant inhibitory effects on xanthine oxidase (IC50 values are 110.0 and 113.0 μg/mL, separately), soluble fractions were also evaluated. Only EtOAc fraction of twig extracts showed better inhibitory effect with IC50 value of 26.6 μg/mL. After acid hydrolysis, the xanthine oxidase inhibitory effect was improved with decreased IC50 value of 15.5 μg/mL. The hydrolyte of EtOAc fraction also had better antioxidant activities. Major myricetin and minor quercetin were identified in the hydrolyte.