Thesis (M.Sc)--Chulalongkorn University, 2008

Discovery of α-glucosidase inhibitors has been actively pursued with the aim of developing therapeutics for the treatment of type 2 diabetes. We have examined the inhibitory effect of Thai medicinal plants against α-glucosidase. The leaves of Aegle marmelos and Corchorus olitorius were selected for this investigation. Bioassay-guided fractionation led to the isolation of active principles. The isolation of dichloromethane and methanol crude extracts from leaves of Aegle marmelos afford three novel phenylethyl cinnamides named anhydromarmeline (1), aegelinosides A (7) and B (8) along with eight known compounds, anhydroaegeline (2), (-)-tembamide (3) dehydroaegeline (4), (-)-aegeline (5), (-)-O-methylether aegeline (6), alangionosides L (9), N-2-ethoxy-2-(4-methoxyphenyl)ethyl-cinnamide (10) and N-(2-(4-hydroxyphenyl) ethyl)-cinnamide (11) as well as four known flavonoid glycosides (12-15). All the isolated compounds from this plant were tested for inhibitory activity against α-glucosidase. The most active principles against α-glucosidase were 14 (IC50 0.34 mM) and 15 (IC50 0.46 mM). In addition, two new flavonoid glycosides named corchorusides A (16) and B (17) together with a known triterpenoid glycoside named capsugenin-25,30-O-β-diglucopyranoside (18) were isolated from methanolic extract of Corchours olitorius leaves. Corchorusides A (16) showed the most inhibitory effect with IC₅₀ value of 0.18 mM.