Flavonol Glycosides with α ‐Glucosidase Inhibitory Activities and New Flavone C ‐Diosides from the Leaves of Machilus konishii

Seventeen flavonoids, five of which are flavone C ‐diosides, 1 – 5 , were isolated from the BuOH‐ and AcOEt‐soluble fractions of the leaf extract of Machilus konishii. Among 1 – 5 , apigenin 6‐ C ‐ β ‐ D ‐xylopyranosyl‐2″‐ O ‐ β ‐ D ‐glucopyranoside ( 2 ), apigenin 8‐ C ‐ α ‐ L ‐arabinopyranosyl‐2″‐ O ‐ β ‐ D ‐glucopyranoside ( 4 ), and apigenin 8‐ C ‐ β ‐ D ‐xylopyranosyl‐2″‐ O ‐ β ‐ D ‐glucopyranoside ( 5 ) are new. Both 4 and 5 are present as rotamer pairs. The structures of the new compounds were elucidated on the basis of NMR‐spectroscopic analyses and MS data. In addition, the 1 H‐ and 13 C‐NMR data of apigenin 6‐ C ‐ α ‐ L ‐arabinopyranosyl‐2″‐ O ‐ β ‐ D ‐glucopyranoside ( 3 ) were assigned for the first time. The isolated compounds were assayed against α ‐glucosidase (type IV from Bacillus stearothermophilus ). Kaempferol 3‐ O ‐(2‐ β ‐ D ‐apiofuranosyl)‐ α ‐ L ‐rhamnopyranoside ( 12 ) was found to possess the best inhibitory activity with an IC 50 value of 29.3 μ M .