Phytochemical study and biological activities of the chemical constituents of Helichrysum pandurifolium Schrank

Abstract

The Cape Floral Kingdom in South Africa is one of six recognised floral kingdoms in the world containing one of the largest concentrates of high density endemic plant species. Over 40 % of the world`s Helichrysum species are found in Southern Africa, many of which have not yet been chemically categorised, and offers a potential resource for new bioactive phytochemicals. Helichrysum plays an important role within many of the South African traditions, historically used as medicine by the native amaXhosa and isiZulu communities. Chemical investigation of Helichrysum pandurifolium Schrank resulted in the isolation of four flavonoids (C1-C4). Chemical structures were elucidated based on their spectroscopic data, the compounds were identified as 5-hydroxy-3,7-dimethoxyflavone (C1), 3,5-dihydroxy-6,7,8- trimethoxyflavone (C2), 3`,4`,7-trihydroxy-3-methoxyflavone (C3) and 5,7-dihydroxy-3- methoxyflavone (C4). In vitro assays used to determine the antioxidant activities for the isolated compounds as well as the total extract include the Ferric ion reducing antioxidant power (FRAP) and Trolox equivalent absorbance capacity (TEAC) assays. The total phenolic content (TPC) of the total extract was also quantified. Anti-diabetic activities were determined via the in vitro inhibition of key digestive enzymes a-glucosidase and a-amylase. Compounds C2-C4 revealed FRAP total antioxidant capacities of IC50 equal to 272.8 ± 7.1; 1183.6 ± 69.7 and 17.6 ± 2.8 μmol AAE/g respectively. Compounds C1-C4 measured TEAC antioxidant activities as 246.8 ± 2.9; 799.8 ± 8.6; 952.9 ± 1.5 and 486.6 ± 3.7 μmol TE/g respectively. Compounds C1-C3 showed a-glucosidase inhibitions of 18.7 ± 2.4; 40.5 ± 11.6 and 3.3 ± 0.4 μg/mL respectively, where compound C3 was found to have and a-amylase inhibition of 116.2 ± 5.8 μg/mL. The total phenolic content of the total extract was quantified to be 108.3 ± 18.9 mg GAE/g and resulted in FRAP, TEAC and a-glucosidase inhibition of 248.2 ± 0.1 μmol AAE/g; 722.4 ± 16.6 μmol TE/g and 126.5 ± 14.3 μg/mL respectively. This is the first report on the isolation and identification of methoxyflavanoids from H. pandurifolium and their biological activities. Results suggest that the isolated phytochemicals may be used as a natural source of anti-diabetic medication by reducing the risk of hyperglycaemia and as preventative medication related to various chronic diseases, however further in-vivo studies will be required.