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

Abstract 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 1H‐ and 13C‐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 IC50 value of 29.3 μM.