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  • Title: An acylated flavonol glycoside and hydrolysable tannins from Callistemon lanceolatus flowers and leaves.
    Author: Marzouk MS.
    Journal: Phytochem Anal; 2008; 19(6):541-9. PubMed ID: 18618463.
    Abstract:
    INTRODUCTION: Callistemon lanceolatus DC. (Myrtaceae) is a plant rich in polyphenols, and is used as anticough, antibronchitis and insecticide in folk medicine. Because of the biological importance of plant polyphenols, particularly tannins, a phytochemical study was of interest to investigate the constitutive poyphenols in the extracts of flowers and leaves. OBJECTIVE: To avoid time-consuming methodology for isolation of a complex mixture of known metabolites, HPLC-ESI/MS was employed for fast picking up of the new compounds followed by identification of the structures with UV and one- and two-dimensional NMR. METHODOLOGY: Flowers and leaves were separately extracted with hot aqueous methanol under reflux (70 degrees C). Pre-isolation of the total extracts was achieved through column chromatographic fractionation on polyamide with water-methanol for gradient elution. The main fractions were purified using repeated column chromatography on cellulose and/or Sephadex LH-20 with suitable eluents. HPLC-ESI/MS analyses were carried out in the single ion monitoring (SIM) and negative ion modes. The pure compounds in methanol-water (1:1) were analysed by direct infusion ESI/MS. Final structure elucidation was obtained by one- and two-dimensional NMR. RESULTS: Two new metabolites namely quercetin 3-O-beta-D-glucuronopyranoside n-butyl ester (1) and n-butylgallate 4-O-(2',6'-di-O-galloyl)-beta-D-glucopyranoside (4) along with nine known ones were identified from the aqueous methanol extracts of flowers and leaves. CONCLUSION: The study has shown that Callistemon lanceolatus is rich in polyphenols. HPLC-ESI/MS may be used, in negative ion mode, as an efficient and rapid analytical tool for investigating complex plant extracts.
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