Thesis (M.Sc.)--Chulalongkorn University, 2011

α-Glucosidase inhibitors and applied as the effective therapeutic approach for treatment of type II diabetes. We have examined the inhibitory effect of Thai medicinal plants against α-glucosidase. The Moringa oleifera leaves and Sesamum indicum defatted seeds, which are edible plants and cultivated in Thailand, were selected for this investigation are Chromatography technique and bioassay-guided fractionation led to the isolation of active components. The isolation of methanol crude extract from M.oleifera leaves afforded two phenolic glycosides named niazirin and pyrrolemarumine 4"-O-α-L-rhamnopyranoside and two flavonoid glycosides named kaempferol-3-O-β-glucopyranoside and quercetin-3-O-β-glucopyranoside. All the isolated compounds were tested for inhibitory activity against α-glucosidase. Only phenolic glycosides selectively inhibited α-glucosidase from baker’s yeast. Niazirin was the most potent α-glucosidase inhibitor against baker’s yeast, which was approximately 8 times more active than that of antidiabetic drug acarbose whereas flavonoid glycosides selectively inhibited that from rat intestine; in which the most active compound quercetin-3-O-β-glucopyranoside inhibited maltase (IC₅₀ 95.73 µM) and sucrase (IC₅₀ 54.80 µM). On the other hands, the isolation of methanol crude extract from S.indicum defatted seeds afforded three lignans named sesamin, sesamolin and pinoresinol. They broadly inhibited α-glucosidase from baker’s yeast (IC₅₀ 0.20-0.49 mM), whereas pinoresinol selectively inhibited maltase from rat intestine (IC₅₀ 0.0343 mM). To gain insight into inhibition mechanism of pinoresinol, kinetic study was carried out. A kinetic analysis showed that pinoresinol inhibited maltase by mixed- type manner. Notably, the inhibition mechanism of pinoresinol is first reported herein.