Anthraquinones and naphthalene derivatives of Rumex confertus

Abstract

Preparations based on Rumex confertus Willd. (Polygonaceae) root possess laxative, anti-inflammatory, hemostatic, bactericidal, hypotensive, sedative, and antitumor properties [1–3]. However, they have yet not found broad application in scientific medicine. In our opinion, this situation can be explained by the inadequate understanding of the chemical composition of R. confertus. In particular, regulations (VFS 42-1007-81) on R. confertus root do not require normalization of the raw material quality with respect to the active ingredients [4]. Furthermore, systematic structural studies of anthraquinones using NMR spectroscopy are missing for several of the anthracene derivatives [5–8]. The goal of our work was to study the constituent composition of anthraquinones and naphthalene derivatives in R. confertus roots. We studied roots of the plant that were collected in May 2011 in the vicinity of Samara. Air-dried roots (200 g) were extracted exhaustively by EtOH (70%), combining maceration (24 h) and subsequent extraction at 85–90°C. The aqueous EtOH extracts were evaporated in vacuo to a viscous residue (~50 mL). The condensed extract was dried on silica gel L 40/100. The resulting powder (extract + silica gel) was placed onto a layer of silica gel formed in CHCl3. The chromatographic column was eluted by CHCl3 and CHCl3:EtOH in various ratios (97:1, 97:2, 97:3, 95:5, 93:7, 90:10, 85:15, 80:20, 70:30, 60:40, 50:50). Separation of the compounds was monitored by TLC on Silufol UV-254 and PTSKh-AF-A-UV plates using CHCl3:EtOH (9:1), CHCl3:MeOH:H2O (26:14:3), and n-BuOH:AcOH (glacial):H2O (4:1:2). The corresponding fractions containing 1, 2, and 4 were combined. Precipitates forming in them were separated and crystallized from aqueous EtOH (2 and 4) or from CHCl3:hexane (1). Fractions containing 3 and 5 were rechromatographed over a column of silica gel L40/100 using a gradient of hexane:CHCl3. Compounds 6 and 7 were purified by rechromatography over a column of polyamide (Woelm, Germany) with elution by CHCl3:EtOH mixtures in various ratios. PMR spectra were taken on Bruker AM 300 instruments (300 MHz). Mass spectra were measured on a Kratos MS-30. UV spectra were recorded on a Specord 40 spectrophotometer (Analytik, Jena). Emodin (1,6,8-Trihydroxy-3-methylanthraquinone) (1) [5]. Orange needle-like crystals, mp 254–255°C (CHCl3:EtOH). C15H10O5. Mass spectrum (70 eV, 200°C, m/z, %): M + 270 (100), 255 (3), 253 (8), 242 (7), 241 (23), 214 (4), 213 (17). UV spectrum (EtOH, max, nm): 222, 250, 268, 290, 439, 461sh. PMR spectrum (300 MHz, DMSO-d6, , ppm, J/Hz): 2.38 (3H, s, CH3-3), 6.55 (1H, d, J = 2.5, H-7), 7.09 (2H, c, H-2, 4), 7.45 (1H, d, J = 2.5, H-5), 11.19 (1H, br.s, 6-OH), 11.92 and 12.00 (1H each, c, OH-1, 8). Emodin 8-O-D-Glucopyranoside (2) [5]. Orange crystals, mp 189–192°C (aqueous EtOH). C21H20O10. Mass spectrum (70 eV, 200°C, m/z, %): M+ aglycon 270 (30), 256 (100). UV spectrum (EtOH, max, nm): 222, 272sh, 285, 422. PMR spectrum (300 MHz, DMSO-d6, , ppm, J/Hz): 2.41 (3H, s, CH3-3), 3.2–4.3 (6H Glc), 5.13 (1H, d, J = 7, H-1 Glc), 7.00 (1H, d, J = 2.5, H-7), 7.14 (1H, s, H-2), 7.28 (1H, d, J = 2.5, H-5), 7.45 (1H, s, H-4), 11,22 (1H, br.s, 6-OH), 13.17 (1H, s, 1-OH). Chrysophanol (1,8-Dihydroxy-3-methylanthraquinone) (3) [5]. Orange needle-like crystals, mp 193–195°C (CHCl3:EtOH). C15H10O4. Mass spectrum (70 eV, 200°C, m/z, %): M + 254 (100), 237 (5), 231 (14), 226 (12), 201 (15), 197 (14). UV spectrum (EtOH, max, nm): 224, 257, 287, 430. PMR spectrum (300 MHz, DMSO-d6, , ppm, J/Hz): 2.43 (3H, s,