FLAVONOIDS FROM ASTRAGALUS TRANSCASPICUS
Abstract
In continuation of our studies on the chemistry of plant flavonoids, we began investigating Astragalus transcaspicus Freyn (Leguminosae). Botanical databases like World Flora Online classify Astragalus transcaspicus under the broader accepted species Astragalus ammodendron. The air-dried, powdered aerial parts (1.5 kg), collected during the fruiting stage in the Republic of Karakalpakstan (Beruniy District), were exhaustively extracted with methanol (8 L Ч 5). The methanolic extracts were concentrated to a syrup-like consistency, diluted with twice the volume of water, and the aqueous solution was successively treated with chloroform, ethyl acetate, and n-butanol. After evaporation of the solvents under vacuum, 38 g of the ethyl acetate extract and 74 g of the n-butanol extract were obtained. The ethyl acetate extract was chromatographed on a silica gel column, and the substances were eluted with a chloroform-methanol (6:1) mixture while increasing the methanol concentration. As a result of rechromatography of the flavonoid fractions, four individual substances were isolated. Compound 1, C22H22O10, m.p. 224-226°C, 154 mg (0.0102%; hereinafter, the yield is calculated based on the air-dried raw material), was identified as biochanin A 7-O-в-D-glucopyranoside. Compound 2, C22H22O11, m.p. 154-156°C, 158 mg (0.0105%), was identified as pratensein 7-O-в-D-glucopyranoside. Compound 3, C21H20O10, m.p. 226-258°C, 87 mg (0.0058%), was identified as genistein 7-O-в-D-glucopyranoside. Compound 4, C21H20O11, m.p. 221-222°C, 95 mg (0.0063%), was identified as orobol 7-O-b-D-glucopyranoside. Compound 5, C28H32O16, m.p. 175-177°C, 78 mg (0.0052%), was identified as isorhamnetin 3-O-rutinoside. All isolated compounds were identified on the basis of their physicochemical constants, chemical transformations, 1H and 13C NMR spectral data, as well as by direct comparison with authentic samples.
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