α-Glucosidase Inhibitors from the Bark Extract of Ethno-Antidiabetic Ceriops tagal (Perr.) C.B. Rob

Abstract

The bark of Ceriops tagal has been used in the Philippines for folk treatment of diabetes mellitus (DM). Through an α-glucosidase inhibition assay guided isolation, constituents from the detannified methanolic bark extract were isolated and identified to be methyl 2,4-dihydroxy-3,6-dimethyl benzoate (1), isopimar-7-ene-15S,16-diol (2), betulinic acid (3), lupeol (4), and methyl 2,4-dihydroxy-6-methyl benzoate (5). Compounds 3 (IC50 = 5.31 µM) and 4 (IC50 = 55.84 µM) showed a more potent activity against α-glucosidase than the positive control, 1-deoxynojirimycin (IC50 = 79.16 µM). This is the first report on the presence of the weakly active compounds (1, 2, and 5) (IC50 > 75 µM) in the genus Ceriops and the first report on the biological activity of Compound 2. Enzyme kinetic studies suggested that betulinic acid is an uncompetitive type of inhibitor, with lupeol as a non-competitive type. This study provides evidence on the possible mechanism of the antidiabetic property of C. tagal associated with its traditional use. It supports the possible utilization of the bark for development to prevent or treat diabetes.