The large genus Centaurea (Asteraceae) comprises about 500 species mostly distributed around the Mediterranean area and in Western Asia [1]. About 50 species grow in Algeria, among which Centaurea calcitrapa, known as Bou Neggar, is largely distributed [2]. C. calcitrapa is used in traditional medicine as antidiabetic and diuretic [3,4]. Several previous chemical studies have been reported on the genus [5][6][7][8][9].Continuing our research on the chemical constituents of Algerian Centaurea species [10-16], we report here the isolation of six flavonoids and a sesquiterpene lactone, cnicin, from the chloroform exudate of the aerial parts of Centaurea calcitrapa L.Fresh aerial parts (1.8 kg) were extracted with a mixture of toluene-ethyl acetate (6:4) twice during 15 min. The obtained solutions were combined and concentrated. During the concentration, a precipitate was formed. This precipitate was filtered and washed with petroleum ether to give a pure white compound 1 (2.65 g) as a major component, identified as cnicin [12]. The residual solution was concentrated to give 11.52 g of extract, which was chromatographed on a silicagel column eluted with a gradient of chloroform-acetone to yield eight fractions, which were purified on preparative TLC Silica gel 60 GF plates eluted with a mixture of CHCl 3 -MeOH-H 2 O (80:9:1) to give compounds 2-7. Purification of each compound for spectral analysis was carried out using MeOH over a Sephadex LH-20 column.The structures of these compounds were established using UV spectroscopy, 1 H and 13 C NMR, and MS analyses. All the data were in good agreement with the respective literature data.Compound 1. C 20 H 26 O 7 , mp 143qC. IR spectrum (KBr, Q, cm -1 ): 1756 (J-lactone), 1707 (C=O conjugated ester), 3385 (OH). Mass spectrum (FAB + , 70 eV), m/z: 379 [M + H] + , 247 [(1c,2c-OH -Et) acrylic acid], 229 [247 -H 2 O]. 1 H NMR (250 MHz, CDCl 3 + 2 drops CD 3 OD, G, ppm, J/Hz): 6.3 (1H, s, H-18c), 6.25 (1H, d, J 13c, 7 = 3.3, H-13c), 6.1 (1H, s, H-18), 5.75 (1H, d, J 13, 7 = 2.7, H-13), 5.2 (1H, t, J 6,5 = J 6,7 = 8.2, H-6), 5.15 (1H, m, H-8), 5.05 (1H, m, H-1), 4.
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