Phenolic compounds from roots of Rhodiola litvinovii

Abstract

Plants of the genus Rhodiola (Crassulaceae) typically have a high content of biologically active compounds. R. rosea (golden root) is a medicinal plant that is used in folk and modern medicine. Therefore, it seemed interesting to study other species of Rhodiola. Four species of this genus are indigenous to Uzbekistan [1]. The chemical composition of the population of R. litvinovii Boriss. growing in Uzbekistan is practically unstudied [2]. Six phenolic compounds were isolated previously from a population of this plant growing in Siberia (Russia) [3–5]. We studied roots of R. litvinovii collected during flowering in the western Tien-Shen (Pskem Range, Bostandyk District, Tashkent Region, RU) in September 2010. For this, roots of R. litvinovii (2000 g) were extracted exhaustively with EtOH (40%) at room temperature by percolation (24 h). The combined extracts were evaporated in vacuo. The condensed thick residue (0.7 L) was diluted with H2O (1:1) and worked up successively with petroleum ether, CHCl3, EtOAc, and n-BuOH. The condensed EtOAc extract was placed on a chromatography column of silica gel that was eluted sequentially with CHCl3 and CHCl3:MeOH mixtures of various proportions. The resulting separate eluates were re-chromatographed over Sephadex LH-20 with elution by H2O:MeOH mixtures with increasing gradient of MeOH. The chromatographic separation isolated four known compounds that were identified by comparing their IR, UV, PMR, and 13C NMR spectra with the literature. p-Tyrosol (p-hydroxyphenyl-ethanol) (1), white needle-like crystals, C8H10O2, mp 94–95°C (CHCl3:MeOH, 4:1). UV spectrum (MeOH, max, nm): 204.36, 223.93, 278.27. IR spectrum (KBr, , cm –1): 3390–3144 (OH), 2879 (CH2), 1613, 1598, 1513 (aromatic ring), 817 (p-substituted benzene ring). 13C NMR spectrum (100 MHz, CD3OD, , ppm): 131.20 (C-1), 130.99 (C-2), 116.28 (C-3), 156.88 (C-4), 116.28 (C-5), 130.99 (C-6), 39.54 (C-7), 64.72 (C-8) [6, 7]. Salidroside [p-hydroxyphenyl-( -D-glucopyranosyl)-ethanol] (2), white amorphous powder with a yellow tint, C14H20O7, mp 163–164°C (CHCl3:MeOH:H2O, 26:14:3). UV spectrum (MeOH, max, nm): 203.06, 223.90, 277.60. IR spectrum (KBr, , cm–1): 3596-3271 (OH), 2933, 2878 (CH2), 1883, 1615, 1518 (benzene ring), 1241 (phenol hydroxyl), 1073, 1023 (pyranoside), 900 ( -glycoside bond). 13C NMR spectrum (100 MHz, CD3OD, , ppm): 131.06 (C-1), 130.80 (C-2), 116.25 (C-3), 146.51 (C-4), 116.25 (C-5), 130.80 (C-6), 36.50 (C-7), 71.77 (C-8), 104.49 (C-1 ), 72.23 (C-2 ), 78.07 (C-3 ), 71.77 (C-4 ), 78.22 (C-5 ), 62.88 (C-6 ) [8]. Gallic acid (3), crystals, very soluble in alcohol and hot water, C7H6O5, mp 238–240°C. UV spectrum (EtOH, max, nm): 211, 274, Rf 0.65 (BAW, 4:1:2), 0.34 (2% AcOH); gave a blue color with iron chloride solution (1%). Identification of gallic acid (3) was confirmed by an XSA. (–)-Epigallocatechin-3-O-gallate (4), brown amorphous powder, C22H18O11, mp 210–211°C. UV spectrum (MeOH, nm): max 205, 275; min 255. IR spectrum (KBr, , cm –1): 3386, 2929, 1728, 1616, 1527, 1451, 1283, 1206, 1046, 776. 13C NMR spectrum (100 MHz, CD3OD, , ppm): 77.22 (C-2), 68.56 (C-3), 25.42 (C-4), 155.83 (C-5), 95.19 (C-6), 156.48 (C-7), 94.53 (C-8), 156.42 (C-9), 98.08 (C-10), 129.44 (C-1 ), 105.54 (C-2 ), 144.89 (C-3 ), 132.40 (C-4 ), 145.29 (C-5 ), 105.54 (C-6 ), 120.17 (C-1 ), 108.91 (C-2 ), 144.89 (C-3 ), 138.39 (C-4 ), 145.29 (C-5 ), 108.91 (C-6 ), 166.20 (COO) [9, 10]. These compounds were isolated for the first time from this plant species.