Flavonoids, Antioxidant and Antibacterial Activities of Eryngium triquetrum

Abstract

The genus Eryngium belongs to the Apiaceae family (Umbelliferae), subfamily Saniculoideae, which consists of about 300 species [1]. Plants of this genus have shown various activities such as anti-inflammatory [2], antimalaria and antifungal [3], antioxidant and antimicrobial [4], antidiabetic [5], and analgesic properties [6]. Air-dried and powdered aerial parts (1.5 kg) of Eryngium triquetrum Vahl. were macerated at room temperature with MeOH–H2O (70:30, v/v) for 24 h three times. After filtration and concentration, the residue was dissolved in water (600 mL). The resulting solution was extracted successively with CHCl3, EtOAc, and n-butanol. Concentration in vacuo led to the following extracts: CHCl3 (0.8 g), EtOAc (1.3 g), and n-butanol (11 g). The butanolic extract of Eryngium triquetrum (11 g) was column chromatographed on polyamide SC6 with a gradient of toluene–MeOH with increasing polarity; Fr. 4 (70 mg), obtained from 85% toluene, was subjected to silica gel column chromatography eluted with EtOAc–MeOH–H2O (10:1:0.5), leading to two subfractions: Fr. 1 and Fr. 2. Subfraction 1 was separated by silica gel column chromatography eluted with CH2Cl2–MeOH (8:2) to afford compound 1 (10 mg). Subfraction 2 yielded compound 2 (60 mg), which was obtained as a yellow precipitate. Fraction 6 (70 mg), obtained from 80% toluene, was further subjected to silica gel column chromatography eluted with EtOAc–MeOH–H2O (10:1:0.5) to give compound 3 (40 mg). The ethyl acetate extract (1.3 g) was column chromatographed on silica gel with a gradient of CHCl3–MeOH with increasing polarity. Fraction 2 (30 mg) and Fr. 3 (35 mg), obtained from 95% and 90% CHCl3 successively, were separated by silica gel column chromatography eluted with EtOAc–MeOH–H2O (10:1:0.5) to afford compounds 4 (9 mg) and 5 (8.5 mg). The structures of compounds 1–5 were established by chemical and spectral analysis, UV, NMR, acid hydrolysis, and HPLC-UVDAD-MS, as well as by comparing their spectroscopic data with those reported in the literature. Acid Hydrolysis. The pure compounds were treated with 2M HCl at 100 C for 1 h. The hydrolysates were extracted with EtOAc, and the aglycons were identified by their UV spectra in methanol and by comparison of their Rf with authentic samples. Sugars were identified in the aqueous residue by comparison with authentic samples on silica gel TLC impregnated with 0.2 M NaH2PO4, solvent Me2CO–H2O (9:1), revealed with aniline malonate. Compound 1. C21H20O11. UV (MeOH, max, nm): 267, 347; +NaOH: 275, 325, 401; +AlCl3: 273, 398; +AlCl3/HCl: 273, 397; +NaOAc: 274, 377; +H3BO3: 268, 355. 1H NMR (250 MHz, CD3OD, , ppm, J/Hz): 8.09 (2H, d, J = 8.9, H-6 , 2 ), 6.91 (2H, d, J = 8.9, H-5 , 3 ), 6.42 (1H, d, J = 1.9, H-8), 6.22 (1H, d, J = 1.9, H-6), 5.28 (1H, d, J = 7.3, Glc H-1 ), 3.26–4.14 (sugar protons). This compound was characterized as kaempferol 3-O-D-glucoside [7]. Compound 2. C30H26O13. UV (MeOH, max, nm): 267, 315; +NaOH: 274, 368; +AlCl3: 274, 403; +AlCl3/HCl: 273, 403; +NaOAc: 274, 372; +H3BO3: 272, 371. 1H NMR (400 MHz, CD3OD, , ppm, J/Hz): 7.97 (2H, d, J = 8.9, H-6 , 2 ), 7.39 (1H, d, J = 15.9, H-7 ), 7.28 (2H, d, J = 8.6, H-2 , 6 ), 6.79 (2H, d, J = 8.9, H-5 , 3 ), 6.77 (2H, d, J = 8.6, H-3 , 5 ), 6.27 (1H, d, J = 1.7, H-8), 6.11 (1H, d, J = 1.7, H-6), 5.24 (1H, d, J = 7.2, Glc H-1 ), 4.32 (1H, d, J = 11.5, H-6 a), 4.19 (1H, dd, J = 12.5, 5.6, H-6 b), 3.20–4.40 (sugar protons). In addition, HPLC-UV-DAD permitted the characterization of the compound as kaempferol 3-O-[6 -O-E-p-coumaroyl]-D-glucopyranoside [8]. Compound 3. C27H30O16. UV (MeOH, max, nm): 269, 314; +NaOH: 276, 321, 365; +AlCl3: 276, 399; +AlCl3/HCl: 277, 399; +NaOAc: 275, 374; +H3BO3: 275, 372. 1H NMR (400 MHz, CD3OD, , ppm, J/Hz): 7.95 (2H, d, J = 8.9, H-6 , 2 ),