Potential antiradical and alpha-glucosidase inhibitors from Ecklonia maxima (Osbeck) Papenfuss

• Alpha-glucosidase inhibitors play a potential role in the treatment of type 2 diabetes.
• Compound (3) had stronger antioxidant activity than ascorbic acid and BHT.
• Compounds 2 and 3 had stronger alpha-glucosidase inhibitory properties than acarbose.
• E. maxima could provide potential antioxidants and alpha-glucosidase inhibitors.

Alpha-glucosidase inhibitors play a potential role in the treatment of type 2 diabetes by delaying glucose absorption in the small intestine. Ecklonia maxima, a brown alga which grows abundantly on the west coast of South Africa, is used to produce alginate, animal feed, nutritional supplements and fertilizer. The crude aqueous methanol extract, four solvent fractions and three phlorotannins: 1,3,5-trihydroxybenezene (phloroglucinol) (1), dibenzo [1,4] dioxine-2,4,7,9-tetraol (2) and hexahydroxyphenoxydibenzo [1,4] dioxine (eckol) (3) isolated from E. maxima were evaluated for antiradical and alpha-glucosidase inhibitory activities. All the phlorotannins tested had strong antioxidant activities on DPPH free radicals with EC50 values ranging from 0.008 to 0.128 μM. Compounds 2 and 3 demonstrated stronger antioxidant activity and an alpha-glucosidase inhibitory property than positive controls. These results suggest that E. maxima could be a natural source of potent antioxidants and alpha-glucosidase inhibitors. This study could facilitate effective utilization of E. maxima as an oral antidiabetic drug or functional food ingredient with a promising role in the formulation of medicines and nutrition supplements.