Polymorphism for Novel Tetraglycosylated Flavonols in an Eco-model Crucifer, Barbarea vulgaris

摘要

Nineteen apparent flavonoids were determined by HPLC-DAD in foliage of a chemotype (G-type) of Barbarea vulgaris, and four were isolated. Two were novel tetraglycosylated flavonols with identical glycosylation patterns, kaempferol 3-O-(2,6-di-O-β-D-glucopyranosyl)-β-D-glucopyranoside-7-O-α-L-rhamnopyranoside (1) and quercetin 3-O-(2,6-di-O-β-D-gmcopyranosyl)-β-D-glucopyranoside-7-O-α-L-rhamnopyranoside (2). The identification of d/l configuration was tentatively based on susceptibility to α-L-rhamnosidase and β-D-glucosidases. A characteristic feature of 1 and 2 was appreciable water solubility, an expected consequence of the extensive glycosylation. A less complex pair of flavonols comprised 3-O-β-D-glucopyranoside-7-O-α-L-rhamnopyranosides of kaempferol and quercetin. Two natural chemotypes of B. vulgaris differed in levels of 1 and 2, with the P-type deficient in 1 and 2 and the insect-resistant G-type rich in 1 (ca. 3—4μmol/g dry wt) and with moderate levels of 2 (ca. 0.3—0.8 μmol/g dry wt). However, there was only modest seasonal variation in flavonols 1 and 2, in contrast to a strong seasonal variation in insect resistance.