α-Glucosidase inhibitory activity was measured using the in vitro method developed by D. Prasanth et al., (Fitoterapia 2001, 72, 686-688). In a micro plate well was taken 50 μL of α-glucosidase enzyme (0.4 U/mL), and treated with 90 μL of 100 mM phosphate buffer (pH 7) and 10 μL test substances (α-mangostin, γ-mangostin and AR 933) or vehicle control. The contents were mixed well and the reaction mixtures were incubated at room temperature for 5 min, and then added 50 μL of p-nitrophenyl α-D-glucopyranose (20 mM) as substrate. The contents were mixed well and again incubated at room temperature for 15 min. The reaction was stopped by the addition of 30 μL of sodium carbonate solution (135 mM). The absorbance was measured at 405 nm using micro plate reader. Control and test blank ODs were obtained by replacing enzyme with buffer. Percentage inhibitions were calculated by comparing mean test OD with mean control OD. {% inhibition=[(COD−TOD)/COD]×100}. The IC50 values were calculated by linear regression analysis of the dose response curve.
