Two very unusual macrocyclic flavonoids from the water lily Nymphaea lotus
Three novel flavonols, myricetin-3′-O-(6″-p-coumaroyl)glucoside and two epimeric macrocyclic derivatives have been isolated from the wild water lily Nymphaea lotus L. This is the first report of such a macrocycle from any source.
Introduction
Nymphaea lotus L. is a water lily, widespread on the River Nile and tributaries in the centre and south of Sudan. The roots of the plant are used throughout this region as a cooked starchy vegetable, while the root and particularly the leaves have been used in traditional Sudanese medicine as a remedy for dysentery, to treat tumours (El Ghazali et al., 1994) and as an antibacterial (Elegami et al., 2001). As a part of a wider study of the Sudanese flora, in particular the use of indigenous plants for the treatment of bacterial infections, we have extracted the dried leaves of the plant and separated the constituents of the biologically active methanol fraction.
Some flavonoid glycosides (Fossen et al., 1998a, Fossen et al., 1999, Fossen & Andersen, 1999), anthocyanins (Fossen et al., 1998b, Fossen & Andersen, 1997) and the hydrolysable tannin geraniin (Kurihara et al., 1993) have previously been isolated from the genus Nymphaea but there have been no reports concerning the chemistry of N. lotus. The present work describes the isolation and identification of two new macrocyclic flavonol glucoside esters and their open-chain precursor.
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Discussion
Fractionation of the methanol extract of the leaves of Nymphaea lotus, using first VLC on silica, then Sephadex LH-20, gave a complex mixture of mainly phenolic metabolites which were separated on a reverse-phase HPLC column using methanol/water as the mobile phase. Two fractions were known compounds, pentagalloyl glucose and myricetin-3-O-rhamnoside. A third was an unidentified ellagic acid derivative. A fourth fraction eluting at 38 min showed the UV characteristics of a flavonoid, with a
General
UV spectra were recorded in absolute methanol using a Unicam UV 300 UV/visible spectrometer. IR data were recorded in KBr disks on a Mattson Genesis series FT-IR. NMR measurements were performed on a Brüker AMX-400 (400 MHz) instrument with C5D5N as solvent. Mass spectra were recorded on a Jeol JMS-AX 505 HA mass spectrometer, using FAB in either positive (nitrobenzyl alcohol matrix) or negative (glycerol matrix) ion mode.
Plant material
The plant material was collected from White Nile province (Sudan) in
Acknowledgements
We thank the Ministry of Higher Education in Sudan and the British Council (Sudan) for financial support of A.E.E; Prof. P.G. Waterman for his interest in the early stages of this work.
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