Isolation of a New Phlorotannin, a Potent Inhibitor of Carbohydrate-Hydrolyzing Enzymes, from the Brown Alga Sargassum patens

Ethanol extracts from 15 kinds of marine algae collected from the coast of the Noto Peninsula in Japan were examined for their inhibitory effects on human salivary a-amylase. Four extracts significantly suppressed the enzyme activity. An inhibitor was purified from the extract of Sargassum patens. The compound was a new phloroglucinol derivative, 2-(4-(3,5-dihydroxyphenoxy)-3,5-dihydroxyphenoxy) benzene-1,3,5-triol (DDBT), which strongly suppressed the hydrolysis of amylopectin by human salivary and pancreatic alpha-amylases. The 50% inhibitory activity (IC50) for alpha-amylase inhibition of DDBT (3.2 mu g/mL) was much lower than that of commercially available alpha-amylase inhibitors, acarbose (26.3 mu g/mL), quercetagetin (764 mu g/mL), and alpha-amylase inhibitor from Triticum aestivum (88.3 mu g/mL). A kinetic study indicated that DDBT was a competitive alpha-amylase inhibitor with a K-i of 1.8 mu g/mL. DDBT also inhibited rat intestinal alpha-glucosidase with an IC50 value of 25.4 mu g/mL for sucrase activity and 114 mu g/mL for maltase activity. These results suggest that DDBT, a potent inhibitor of carbohydrate-hydrolyzing enzymes, may be useful as a natural nutraceutical to prevent diabetes.