α-glucosidase inhibitors from leaves and seeds of moringa Moringa oleifera

Abstract

Moringa oleifera is an edible plant that has long been used for diabetes therapy. In Thailand, leaves and seeds of M. oleifera are sold in many forms such as herbal infusion and capsule, and used to suppress blood glucose level. To proof this claim, the components responsible for this activity were identified using bioassay-guided isolation. The isolation of aqueous and methanolic extracts of leaves together with methanolic extract of seeds yielded nine compounds named p-hydroxybenzaldehyde-O--L-rhamnopyranoside, keampferol, kaempferol-3-O-β-glucopyranoside, 1-O-(4-hydroxymethylphenyl)-α-L-rhamnopyranoside, 4-methoxybenzene-1,3-diol, p-hydroxybenzoic acid, N,N-Bis(4-hydroxybenzyl) urea, uridine as well as new amide derivative named ME51-4. All the isolated compounds were tested for inhibitory activity against α-glucosidase. Only keampferol and kaempferol-3-O-β-glucopyranoside, which were isolated from leaves aqueous extract, broadly inhibited α-glucosidases intestinal from baker’s yeast and rat intestine. However, kaempferol inhibited α-glucosidase with more slightly improved inhibition than kaempferol-3-O-β-glucopyranoside. Due to highly potent inhibition of keampferol and kaempferol-3-O-β-glucopyranoside, the consumption of M. oleifera leaves in form of herbal infusion would result in higher effective control of blood glucose level and diabetes therapy.