Flavonoids and sterols from Alhagi sparsifolia

Abstract

Alhagi sparsifolia Shap. (Leguminosae) is widely distributed in Xinjiang Autonomous Region of the PRC and has been used for centuries in folk medicine. Catechins and proanthocyanidins were isolated and studied previously [1]. The aerial part (5 kg) of A. sparsifolia was extracted with ethanol (70%, 3×). The combined alcohol extract was distilled in vacuo. The condensed residue was diluted with water and extracted successively with petroleum ether, ethylacetate, and n-butanol. The petroleum ether fraction was chromatographed over a column of Al2O3 with elution by petroleum ether:diethylether to isolate 1 and 2. The ethylacetate fraction was chromatographed over a column of silica gel with graident elution by CHCl3:CH3OH to isolate 3. Chromatography of the butanol fraction over a column using CHCl3:CH3OH isolated 4 and 5. Compounds 1 and 2 were identified as stigmasterol and β-sitosterol, respectively, by direct comparison with authentic samples. PMR and 13C NMR spectra were used to identify 3-5. Isorhamnetin (3), C16H12O7, mp 272-275°C. PMR spectrum (600 MHz, DMSO-d6, δ, ppm, J/Hz): 12.47 (1H, 5-OH), 10.80 (1H, br.s, 7-OH), 9.75 (1H, br.s, 3-OH), 9.42 (1H, br.s, 4′−OH), 7.75 (1H, d, J = 2.4, 2′-H), 7.69 (1H, dd, J = 2.4, 8.8, 6′-H), 6.94 (1H, d, J = 8.8, 5′-H), 6.48 (1H, d, J = 2.4, 8-H), 6.19 (1H, d, J = 2.4, 6-H), 3.84 (3H, s, –OCH3). 13C NMR spectrum (150 MHz, DMSO-d6, δ, ppm): 147.34 (C-2), 135.81 (C-3), 175.86 (C-4), 160.67 (C-5), 98.20 (C-6), 163.94 (C-7), 93.58 (C-8), 156.15 (C-9), 102.99 (C-10), 121.95 (C-1′), 111.67 (C-2′), 148.78 (C-3′), 146.59 (C-4′), 115.52 (C-5′), 121.70 (C6′), 55.75 (–OCH3) [2]. Isorhamnetin-3-O-glucoside (4), C22H22O12, mp 205-208°C. PMR spectrum (600 MHz, DMSO-d6, δ, ppm, J/Hz): 7.95 (1H, d, J = 2.4, 2′-H), 7.60 (1H, d, J = 8.4, 2.4, 6′-H), 6.92 (1H, d, J = 8.4, 5′-H), 6.39 (1H, d, J = 2.4, 6-H), 6.20 (1H, d, J = 2.4, 8-H), 5.43 (1H, d, J = 6.6, 1′′-H), 3.98 (3H, s, 3′–OCH3), 3.15-3.80 (m, sugar protons). 13C NMR spectrum (150 MHz, DMSO-d6, δ, ppm): 158.3 (C-2), 135.2 (C-3), 179.3 (C-4), 162.9 (C-5), 99.8 (C-6), 166.0 (C-7), 94.7 (C-8), 158.5 (C-9), 105.6 (C-10), 123.7 (C-1′), 114.3 (C-2′), 150.7 (C-3′), 148.3 (C-4′), 116.0 (C-5′), 123.0 (C-6′), 103.6 (C-1′′), 73.8 (C-2′′), 75.9 (C-3′′), 71.4 (C-4′′), 78.0 (C-5′′), 62.5 (C-6′′), 56.7 (3′-OCH3) [3-4]. Isorhamnetin-3-O-rutinoside (5), C28H32O16, mp 178-180°C. PMR spectrum (600 MHz, DMSO-d6, δ, ppm, J/Hz): 12.59 (1H, br.s, 5-OH), 10.87 (1H, br.s, 7-OH), 9.82 (1H, br.s, 4′-OH), 7.87 (1H, d, J = 2.4, 2′-H), 7.52 (1H, dd, J = 2.4, 8.8, 6′-H), 6.91 (1H, d, J = 8.8, 5′-H), 6.44 (1H, d, J = 2.4, 6-H), 6.21 (1H, d, J = 2.4, 8-H), 5.45 (1H, d, J = 9.2, 1′′-H), 5.14 (1H, d, J = 4.0, 1′′′-H), 3.84 (3H, 3′-OCH3), 3.00-3.80 (m, sugar protons), 0.98 (3H, d, J = 6.0, 6′′′-H). 13C NMR spectrum (150 MHz, DMSO-d6, δ, ppm): 157.1 (C-2), 133.6 (C-3), 177.9 (C-4), 161.8 (C-5), 99.3 (C-6), 164.8 (C-7), 94.4 (C-8), 157.1 (C-9), 104.6 (C-10), 121.6 (C-1′), 115.8 (C-2′), 150.0 (C-3′), 147.5 (C-4′), 113.8 (C-5′), 122.8 (C-6′), 101.8 (C-G1), 74.9 (CG2), 77.0 (C-G3), 71.2 (C-G4), 76.5 (C-G5), 67.4 (C-G6), 101.5 (C-R1), 70.7 (C-R2), 70.9 (C-R3), 72.4 (C-R4), 68.9 (C-R5), 18.3 (C-R6), 56.2 (3′-OCH3) [2]. Flavonoids and sterols were isolated for the first time from A. sparsifolia.