Isolation of Dihydroquercetin and its Glycoside …….Ali Alkaf, Nasser A. Awadh,Nasr Ghaleb Univ. Aden J. Nat. and Appl. Sc. Vol. 17 No.3 – December 2013 711 Isolation of Dihydroquercetin and its Glycoside Dihydroquercetin- rhamnoside from Catha edulis Forsk Ali Gamal Alkaf 1 , Nasser A. Awadh 2 and Nasr Abdo Ghaleb 3 Medicinal Chemistry Department 1 , Faculty of Pharmacy, Sana'a University; Pharmacognosy Department 2 , Faculty of Pharmacy, Sana'a University ; Pharmaceutical Chemistry Department 3 , Faculty of Pharmacy, Aden University, Yemen. alinasser9678@yahoo.com Abstract Fractionation of the stem extract, from Catha edulis has resulted in the isolation of two known aglycones dihydroquercetin: (a) taxifolin, and (b) dihydromyricitin, ampelopsin.. Fractionation of leaf extract resulted in the isolation of 4 flavonoid glycosides dihydroquercetin: rhamnoside astilbin; dihydromyricetin 3-O-rhamnoside; myricetin-3-O-L-rhamnoside, myricitrin, and quercetin-3-L-galactoside. Dihydroquercetin taxifolin (in the stem), and dihydroquercetin – rhamnoside astilbin (in the leaves) have been reported for the first time in Khat plant. All isolated compounds were identified by means of chromatographic and spectral methods (UV-VIS, IR, 1 H- NMR). Key words: Catha edulis, flavonoids, dihydroquercetin, dihydroquercetin – rhamnoside. Introduction Catha edulis is a plant that grows in certain areas of East Africa and the Arab Peninsula. A large number of people chew khat leaves because of its pleasurable and stimulating effects. Khat chewing is found to have a subjective effect on human beings [4, 6]. The chemical constituents of khat leaves include (-) cathinone, (+)-norpseudoephedrine, ethereal oils, sterols, triterpeues, flavonoids, tannins, ascorbic acid etc [3,7]. A number of flavonoids have been reported from Catha edulis [2, 5]. In this short communication, the isolation of six known flavonoids, of which two have not been previously reported, has been reported. Materials and methods General experimental procedures Melting points were determined on Mel-Tep II , spectral data were recorded by using the following instruments: UV/Vis-Spectrophotometer; perkin-Elmers55s, Infrared spectrophotometer, type unicam SP 1000, NMR Varian VXR-300 FT spectrometer operating at 299.949 MHz for H- NMR. Analytical TLC, Merck silicagel 60 F 254 precoated plates; and chromatograms were visualised under UV light at 254 and 366 nm, and/or sprayed with Komarowsky or Cerium Sulphate or Naturstoff reagent A-PEG reagents. Sephadex LH-20 (Pharmacia Fin Chemicals). Plant material Leaves and stems of Catha edulis (Fam: Celasteraceae) were collected from Khat plantation in Dahlah Province, Dahlah district, in March 2002, and the plant was kindly authenticated in the Faculty of Agriculture, Aden University. A voucher specimen was deposited in Pharmaceutical Academy, Pyatigorsk, Russia. Isolation of flavonoids of stem extract: The air-dried powdered stems (2 Kg) of Catha edulis were extracted with 80%. Combined alcoholic extracts were evaporated to dryness and residue was suspended in water, defatted with n- hexane and extracted with ethylacetate till it was free from flavonoidal pigments. Cellulose –full packed column was prepared and washed with chloroform and 96 % ethanol consecutively; ethyl acetate fraction was applied over the column and eluted firstly with 96% ethanol and then eluted gradiently with aqueous in decreased concentrations of ethanol. By using the mixture of ethanol water (2:1), a fraction containing two flavonoids (two spots on TLC: K1 and K2). The eluate was