Flavonol tetraglycosides and other constituents from leaves of Styphnolobium japonicum (Leguminosae) and related taxa

Flavonoid glycosides of the black locust tree, Robinia pseudoacacia (Leguminosae)

Four flavone glycosides isolated from extracts of the leaves of Robinia pseudoacacia (Leguminosae) were characterised by spectroscopic and chemical methods as the 7-O-beta-d-glucuronopyranosyl-(1-->2)[alpha-l-rhamnopyranosyl-(1-->6)]-beta-d-glucopyranosides of acacetin (5,7-dihydroxy-4'-methoxyflavone), apigenin (5,7,4'-trihydroxyflavone), diosmetin (5,7,3'-trihydroxy-4'-methoxyflavone) and luteolin (5,7,3',4'-tetrahydroxyflavone). Assignment of glycosidic (1)H and (13)C resonances in their NMR spectra was facilitated by (2)J(HC) correlations detected using the H2BC (heteronuclear two-bond correlation) pulse sequence. Spectroscopic analysis of two known triglycosides, acacetin 7-O-beta-d-glucopyranosyl-(1-->2)[alpha-l-rhamnopyranosyl-(1-->6)]-beta-d-glucopyranoside (previously unrecorded from this species) and acacetin 7-O-beta-d-xylopyranosyl-(1-->2)[alpha-l-rhamnopyranosyl-(1-->6)]-beta-d-glucopyranoside ('acacetin trioside'), enabled inconsistencies in the literature relating to these structures to be resolved. Comparison of the flavonoid chemistry of leaves and flowers of R. pseudoacacia using LC-UV and LC-MS showed that flavone 7-O-glycosides, particularly of acacetin, predominated in the former, whereas the latter comprised mainly flavonol 3,7-di-O-glycosides, including several examples new to this species. Tissue dependent differences in flavonoid chemistry were also evident from the glycosylation patterns of the compounds.

Assigning glucose or galactose as the primary glycosidic sugar in 3-O-mono-, di- and triglycosides of kaempferol using negative ion electrospray and serial mass spectrometry

Kaempferol 3-O-beta-glucopyranoside, kaempferol 3-O-beta-galactopyranoside and higher glycosides of these two flavonoids with alpha-rhamnose at C-2 and/or C-6 of the primary sugar were studied by negative ion electrospray ionisation and serial mass spectrometry in a three-dimensional (3D) ion trap mass spectrometer. Kaempferol 3-O-beta-glucopyranoside and kaempferol 3-O-alpha-rhamnopyranosyl(1-->6)-beta-glucopyranoside could be distinguished from their respective galactose analogues by differences in the ratio of the radical aglycone ion [Y(0) - H](*-) to the rearrangement aglycone ion Y(0) (-) following MS/MS of the deprotonated molecules. Kaempferol 3-O-rhamnopyranosyl(1-->2)-beta-glucopyranoside and kaempferol 3-O-alpha-rhamnopyranosyl(1-->2)[alpha-rhamnopyranosyl(1-->6)]-beta-glucopyranoside could be distinguished from their respective galactose analogues by differences in the product ion spectra of the [(M - H) - rhamnose](-) ion following serial mass spectrometry. In the triglycoside, it was deduced that this ion resulted from the loss of the rhamnose substituted at 2-OH of the primary sugar by observing that MS/MS of deprotonated kaempferol 3-O-beta-glucopyranosyl(1-->2)[alpha-rhamnopyranosyl(1-->6)]-beta-glucopyranoside showed the loss of glucose and not rhamnose. Thus the class of sugar (hexose, deoxyhexose, pentose) at C-2 and C-6 of the primary sugar can be determined. These observations aid the assignment of kaempferol 3-O-glycosides, having glucose or galactose as the primary glycosidic sugar, in LC/MS analyses of plant extracts, and this can be done with reference to only a few standards.

Flavonol tetraglycosides from fruits of Styphnolobium japonicum (Leguminosae) and the authentication of Fructus Sophorae and Flos Sophorae

The dried fruits and seeds of Styphnolobium japonicum (L.) Schott (syn. Sophora japonica L.) are used in traditional Chinese medicine and known as Fructus Sophorae or Huai Jiao. The major flavonoids in these fruits and seeds were studied by LC-MS and other spectroscopic techniques to aid the chemical authentication of Fructus Sophorae. Among the flavonoids were two previously unreported kaempferol glycosides: kaempferol 3-O-beta-glucopyranosyl(1-->2)-beta-galactopyranoside-7-O-alpha-rhamnopyranoside and kaempferol 3-O-beta-xylopyranosyl(1-->3)-alpha-rhamnopyranosyl(1-->6)[beta-glucopyranosyl(1-->2)]-beta-glucopyranoside, the structures of which were determined by NMR. Two further tetraglycosides were identified for the first time in S. japonicum as kaempferol 3-O-beta-glucopyranosyl(1-->2)[alpha-rhamnopyranosyl(1-->6)]-beta-glucopyranoside-7-O-alpha-rhamnopyranoside and kaempferol 3-O-beta-glucopyranosyl(1-->2)[alpha-rhamnopyranosyl(1-->6)]-beta-galactopyranoside-7-O-alpha-rhamnopyranoside; the latter was the main flavonoid in mature seeds. The chromatographic profiles of 27 recorded flavonoids were relatively consistent among fruits of similar ages collected from five trees of S. japonicum, and those of maturing unripe and ripe fruits were similar to a market sample of Fructus Sophorae, and thus provide useful markers for authentication of this herbal ingredient. The flower buds (Huai Mi) and flowers (Huai Hua) of S. japonicum (collectively Flos Sophorae) contained rutin as the main flavonoid and lacked the flavone glycosides that were present in flower buds and flowers of Sophora flavescens Ait., reported to be occasional substitutes for Flos Sophorae. The single major flavonoid in fruits of S. flavescens was determined as 3'-hydroxydaidzein.

Flavonol pentaglycosides of Cordyla (Leguminosae: Papilionoideae: Swartzieae): distribution and taxonomic implications

A survey of foliar flavonoids in the swartzioid legume genus Cordyla s.l. revealed that three species, C. haraka, C. pinnata and C. richardii, were rich in flavonol pentaglycosides. Their structures were elucidated by spectroscopic and chemical methods as the 3-O-alpha-L-rhamnopyranosyl(1-->3)-alpha-L-rhamnopyranosyl(1-->2)[alpha-L-rhamnopyranosyl(1-->6)]-beta-D-galactopyranoside-7-O-alpha-L-rhamnopyranosides of quercetin and kaempferol (cordylasins A and B, respectively). These compounds were not found in the remaining species, C. africana, C. densiflora, C. madagascariensis (two subspecies) and C. somalensis, which exhibited different profiles of flavonoid glycosides. The distribution of flavonol pentaglycosides in Cordyla s.l. does not support a recent proposal to place both C. haraka and C. madagascariensis in the genus Dupuya [Kirkbride, J.H., 2005. Dupuya, a new genus of Malagasy legumes (Fabaceae). Novon 15, 305-314]. The generic relationship between Cordyla s.l. and Mildbraediodendron is also reassessed on the basis of chemical characters, as the O-linked tetrasaccharide that characterises cordylasins A and B is the same as that found in mildbraedin (kaempferol 3-O-alpha-l-rhamnopyranosyl(1-->3)-alpha-l-rhamnopyranosyl(1-->2)[alpha-l-rhamnopyranosyl(1-->6)]-beta-D-galactopyranoside), the main foliar flavonoid of Mildbraediodendron excelsum. Mildbraedin itself was found to be a minor constituent of leaflet extracts of C. haraka, C. pinnata and C. richardii, and a major constituent of C. somalensis.