Biochemical Systematics and Ecology 30 (2002) 1097–1100 www.elsevier.com/locate/biochemsyseco
Flavonoid C-glucosides and a lignan from Centaurea macrocephala (Compositae) N.L. Ribeiro a, L. Nahar b, Y. Kumarasamy a, N. Mir-Babayev a, S.D. Sarker a,∗ a
School of Pharmacy, Phytopharmaceutical Research Laboratory, The Robert Gordon University, Schoolhill, Aberdeen AB10 1FR, UK b Japps Labs, Department of Chemistry, University of Aberdeen, Meston Walk, Old Aberdeen, Aberdeen AB24 3UE, UK Received 20 November 2001; accepted 22 January 2002
Keywords: Centaurea macrocephala; Compositae; Asteraceae; Flavonoid; Isoorientin; Lignan; Arctigenin; Chemotaxonomy
1. Subject and source Centaurea macrocephala Muss. Puschk. ex Willd. (Family: Compositae alt. Asteraceae), commonly known as ‘big-head knapweed’, is a splendid border plant with large, yellow, thistle-like flower heads, indigenous to Armenia, Azerbaijan and Turkey, and also naturalised elsewhere (USDA-ARS-GRIN database, 2001). Seeds of this plant (cat. no. 306) were purchased from an authentic seed supplier, Chiltern Seeds, Bortree Stile, Ulverston, Cumbria LA12 7PB, UK, plants were grown from these seeds in the greenhouse of School of Pharmacy, The Robert Gordon University, Aberdeen and harvested during September 2000. A voucher specimen (SDS2001A) has been deposited in the herbarium of Plant and Soil Science Department, University of Aberdeen, Scotland (ABD).
∗
Corresponding author. Tel.: +44-1224-262547; fax: +44-1224-262555. E-mail address:
[email protected] (S.D. Sarker).
0305-1978/02/$ - see front matter 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 3 0 5 - 1 9 7 8 ( 0 2 ) 0 0 0 4 6 - 7
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2. Previous work Four O-glycosylflavonol (isoquercitrin, 3-O-glucosyl-isorhamnetin, trifolin, and rutin), two C-glycosylflavones (isoscoparin and isovitexin) (Reynaud et al., 1992) and a number of polyacetylenic compounds (Bohlmann and Laser, 1970) have previously been isolated from the leaves of C. macrocephala.
3. Present study Freeze-dried and ground aerial parts (5.1 g) of C. macrocephala were Soxhletextracted, successively, with n-hexane, EtOAc and MeOH. The MeOH extract was subjected to Sep-Pak C18 (10 g) column eluting with step gradient: 30, 60, 80 and 100% MeOH in water (100 ml each). Preparative-HPLC (LUNA C18 preparative column, eluted with a gradient—water: MeOH ⫽ 70:30–0:100 in 30 min, and then 100% MeOH for 5 min, 20 ml/min, monitored by photo-diode-array detector) of the Sep-Pak fraction (60% MeOH) afforded two 6-C-glucosyl flavones, 6-C-glucosyl luteolin (isoorientin, 1, 1.1 mg, ret. time: 7.52 min) (Kuo et al., 1996; Krauze and Cisowski, 1992) and 6-C-glucosyl apigenin (isovitexin, 2, 1.4 mg, ret. time: 9.92 min) (Cheng et al., 2000; Reynaud et al., 1992; Mabry et al., 1970), and a lignan, arctigenin (3, 2.1 mg, ret time: 15.58 min) (Rahman et al., 1990; Nishibe et al., 1984). The structures of these compounds (1–3) were confirmed by UV, 1H and 13C NMR, and FABMS analyses, and all these data were in good agreement with respective literature data.
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4. Chemotaxonomic and ecological significance This is the first report on the isolation 6-C-glucosyl luteolin (isoorientin, (1) and arctigenin (3) from the aerial parts of C. macrocephala. Apart from Compositae, a number of species from other families, Cucurbitaceae, Gentianaceae, Geraniaceae, Polygonaceae, Passifloraceae, Ranunculaceae, Thymelaeaceae, Verbanaceae, etc. also produce 6-C-glucosyl flavones like 1 and 2 (Harborne and Baxter, 1999: ISI Web of Science database, 2001). However, such C-glucosides are not of common occurrence within the genus Centaurea. The butyrolactone type lignan, arctigenin (3) has been found in several other species of Centaurea, e.g. C. scoparia (Youssef and Frahm, 1995), C. solstitialis (Bruno et al., 1991; Tesevic et al., 1998), C. cuneifolia (Aslan and Oksuz, 1999), C. calcitrapa (Marco et al., 1992), C. dealbata and C. montana (Christensen and Lam, 1991a), C. nervosa and C. phrygia (Christensen and Lam, 1991b), etc.
Acknowledgements We thank EPSRC National Mass Spectrometry Service Centre (Department of Chemistry, University of Wales Swansea, Swansea, UK) for FABMS analysis and Raymond Reid (School of Pharmacy, RGU) for technical assistance.
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