Flavonoids from blue flowers of Nymphaèa caerulea

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Abstract

Seven flavonols including the novel 3-(2″-acetylrhamnosides) of myricetin and quercetin (2 and 6), the rare kaempferol 3-(2″-acetylrhamnoside) and quercetin 3-(3″-acetylrhamnoside), in addition to the 3-rhamnosides of kaempferol, quercetin and were isolated from blue flowers of the African water lily Nymphaèa caerulea (=Nymphaèa capensis). Their structures were elucidated by a combination of chromatography and homo- and heteronuclear two-dimensional NMR techniques and electrospray MS for compound 2.

Introduction

Anthocyanin-based flower colours are in general influenced by several factors, including copigmentation with other flavonoids (Brouillard & Dangles, 1994). The water lilies (Nymphaèaceae) show a wide range of flower colours, embracing white, yellow, red and blue nuances (Beckett, 1984). Recently, myricetin 3-O-(α-rhamnopyranosyl(1→6)β-galactopyranoside) was isolated from the leaves and the 3′-xylosides of kaempferol, quercetin and quercetin 3-methyl ether from the red flowers of Nymphaèa × marliacea (Fossen, Frøystein, & Andersen, 1998a). The anthocyanins cyanidin 3-(2″-galloyl-6″-acetylgalactoside), and the 3-(2″-galloyl-6″-acetylgalactoside), 3-(6″-acetylgalactoside), 3-(2″-galloylgalactoside) and 3-galactoside of delphinidin have been found in different proportions in both flowers and leaves of N. × marliacea cultivars with red, pink and white flowers (Fossen, Larsen, & Andersen, 1998b), and the 3-(2″-galloylgalactosides) of delphinidin and cyanidin in leaves of two Victoria species (Strack, Wray, Metzger, & Grosse, 1992). From the blue flowers of the African water lily N. caerulea the unusual anthocyanins, 3′-(2″-galloylgalactoside) and 3′-(2″-galloyl-6″-acetylgalactoside) of delphinidin, have recently been identified (Fossen & Andersen, 1998). In this paper we report on the isolation and structure identification of seven flavonol 3-rhamnosides from the blue flowers of this latter species.

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Results and discussion

The methanolic extract of N. caerulea petals was purified by partition against ethyl acetate followed by purification with column chromatography (Amberlite XAD-7 and Sephadex LH-20) and finally preparative HPLC. The pure flavonoids were checked for homogeneity by analytical HPLC. The compounds 1, 3 and 4, were identified as the 3-O-α-rhamnopyranosides of myricetin, quercetin and kaempferol, respectively. The 1H and 13C resonances for these flavonols were assigned by a combination of 1D and 2D 1H

Plant material

Flowers (500 g) of the African water lily N. caerulea (=N. capensis) were collected in September 1997 from Wamiko water pond, west of Kampala, Uganda. A voucher specimen has been deposited at Makerere University herbarium, Uganda.

Isolation of pigments

The flowers were cut into pieces and extracted with 5% acetic acid in MeOH at 5°C. The filtered extract was concd under red. pres., purified by partition against ethyl acetate and applied to an Amberlite XAD-7 column (Andersen, 1988). The flavonoids in this purified

Acknowledgements

T. F. gratefully acknowledges the Norwegian Research Council for a fellowship. The authors acknowledge the Norwegian Universities' Committee for Development, Research and Education (NUFU) for financial support.


References (11)

  • T. Masuda et al.

    Phytochemistry

    (1991)
  • V. Ossipov et al.

    Biochem. Syst. Ecol.

    (1995)
  • D. Strack et al.

    Phytochemistry

    (1992)
  • I. Tvaroska et al.
  • Ø.M. Andersen

    Acta Chem. Scand. B

    (1988)
There are more references available in the full text version of this article.
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