Characterization of Secondary Metabolites from Purple Ipomoea batatas Leaves and Their Effects on Glucose Uptake

Ipomoea batatas has long been used in folk medicine for the treatment of hyperglycemia or as a food additive for the prevention of type 2 diabetes. However, neither the plant extract nor its active components have been evaluated systematically. In this work four crude extracts, including n-hexane- (IBH), 95% MeOH- (IBM), n-BuOH- (IBB), and H2O-soluble (IBW) fractions, were prepared by fractionation of a methanolic extract of purple I. batatas leaves. Twenty-four pure compounds 1–24 were then isolated by various chromatographic techniques and their structures identified from NMR and MS data. Glucose uptake assays in differentiated 3T3-L1 adipocytes and rat primary hepatocytes, as well as western blot analysis, were carried out to evaluate the antidiabetic activity of this species. The IBH crude fraction, with methyl decanoate (22) as a major and active compound, showed the greatest effect on glucose uptake, most likely via activation of Glut4 and regulation of the PI3K/AKT pathway. Quercetin 3-O-β-d-sophoroside (1), quercetin (3), benzyl β-d-glucoside (10), 4-hydroxy-3-methoxybenzaldehyde (12), and methyl decanoate (22) could be important components contributing to the antidiabetic effects. We conclude that purple I. batatas leaves have potential as an antidiabetic plant source and the active constituents 1, 3, 10, 12, and 22 are promising lead candidates for future investigation.