Acylated flavonol monorhamnosides, α-glucosidase inhibitors, from Machilus philippinensis

Bioassay-guided fractionation and isolation of the active constituents from the leaf extract of Machilus philippinense Merr. yielded two active compounds, kaempferol-3-O-alpha-L-rhamnopyranoside 3 '',4 ''-di-E-p-coumaroic acid ester (1) and 3 ''-E,4 ''-Z-di-p-coumaroic acid ester (2) when tested against a Bacillus stearothermophilus, a or.-glucosidase type IV. The IC(50) values of 1 and 2 were 6.10 and 1.00 mu M, respectively. Further application of the HPLC-SPE-NMR hyphenated technique in the on-line characterization of other active ingredients present in the CH(2)Cl(2) - Soluble fraction led to identification of luteolin (3) and seven additional 3-O-(coumaroyl-rhamnopyranosyl)-flavonols (4-10). Their structures were determined mainly by (1)H NMR spectroscopic analyses. Among the compounds identified, compounds 2, 4, 5, and 7 were hitherto unknown natural products. (C) 2008 Elsevier Ltd. All rights reserved.