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

Four flavone glycosides isolated from extracts of the leaves of Robinta pseudoacacia (Legurninosae) were characterised by spectroscopic and chemical methods as the 7-O-beta-D-glucuronopyi-anosyl-(1 -> 2)[alpha-L-rhamnopyranosyl-(1 -> 6)]beta-D-glucopyranosides of acacetin (5,7-diliydroxy-4'-metlioxyflavone), apigenin (5,7.4'-triliydroxyflavone), diosmetin (5,7.3'-trillydroxy-4'-methoxyflavone) and luteolin (5,7,3',4'-tetra hydroxyflavone) Assignment of glycosidic (1)H and (13)C resonances in their NMR spectra was facilitated by (2)J(HC) correlations detected using the H2BC (licteronuclear two-bond correlation) Pulse sequence Spectroscopic analysis of two known triglycosides, acacetin 7-O-beta-D-glucopyranosyl-(1 -> 2)[alpha-L-rhamnopyranosyl-(1 - 6)l-li-D-glUCOpyranoside (previously unrecorded from this species) and acacetill 7-O-beta-D-xyloyranosyl-(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 ofR pseudoacacia using LC-UV and LC-IVIS showed that flavone 7-O-glycosides, particularly of acacetin. predominated in the former, whereas the latter comprised mainly flavonol 3,7-di-O-glycos ides, including several examples new to this species. Tissue dependent differences in flavonoid chemistry were also evident from the glycosylation patterns of the compounds (C) 2009 Elsevier Ltd All rights reserved