An acylated flavonol glycoside and hydrolysable tannins from Callistemon lanceolatus flowers and leaves.
BACKGROUND
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.


METHODS
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.


CONCLUSIONS
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.
Marzouk
Mohamed S A
MS
Natural Products Group, Nobel Project, National Research Centre, El-Behoos St 31, Dokki, Cairo, Egypt. msmarzouk@yahoo.co.uk
D002851:Chromatography, High Pressure Liquid / Q000191:economics / Q000379:methods; D005707:Gallic Acid / Q000031:analogs & derivatives* / Q000032:analysis; D005960:Glucosides / Q000032:analysis*; D047348:Hydrolyzable Tannins / Q000032:analysis*; D009682:Magnetic Resonance Spectroscopy; D000432:Methanol / Q000737:chemistry; D027822:Myrtaceae / Q000737:chemistry*; D035261:Plant Components, Aerial / Q000737:chemistry; D010936:Plant Extracts / Q000737:chemistry; D010946:Plants, Medicinal / Q000737:chemistry*; D011794:Quercetin / Q000031:analogs & derivatives* / Q000032:analysis; D021241:Spectrometry, Mass, Electrospray Ionization / Q000191:economics / Q000379:methods; D013056:Spectrophotometry, Ultraviolet
D005960:Glucosides; D047348:Hydrolyzable Tannins; D010936:Plant Extracts; D005707:Gallic Acid; D011794:Quercetin; D000432:Methanol