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.
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