Abstract
C18H16O8, monoclinic, P21/n, (no. 14), a = 7.9253(3) Å, b = 16.8928(6) Å, c = 11.8439(5) Å, β = 92.387(2)°, V = 1584.29(11) Å3, Z = 4, Rgt(F) = 0.043, wRref(F2) = 0.102, T = 295(2) K.
The asymmetric unit of the title crystal structure is shown in the figure. Tables 1 and 2 contain details on crystal structure and measurement conditions and a list of the atoms including atomic coordinates and displacement parameters.
Data collection and handling.
| Crystal: | Yellow block |
| Size: | 0.30 × 0.22 × 0.14 mm |
| Wavelength: | Mo Kα radiation (1.54178 Å) |
| μ: | 10.2 cm−1 |
| Diffractometer, scan mode: | Bruker AXS, φ and ω |
| 2θmax, completeness: | 118.2°, >99% |
| N(hkl)measured, N(hkl)unique, Rint: | 32631, 2274, 0.089 |
| Criterion for Iobs, N(hkl)gt: | Iobs > 2 σ(Iobs), 1510 |
| N(param)refined: | 242 |
| Programs: | SHELX [10], Bruker programs [11], OLEX2 [12] PLATON [13] |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2).
| Atom | x | y | z | Uiso*/Ueq |
|---|---|---|---|---|
| O1 | 0.5544(2) | 0.66230(9) | 0.31502(14) | 0.0388(5) |
| O2 | 0.4170(2) | 0.52051(9) | 0.25114(15) | 0.0443(5) |
| O3 | 0.0958(2) | 0.52054(10) | 0.14519(18) | 0.0597(6) |
| H3 | 0.1471 | 0.4831 | 0.1744 | 0.090* |
| O4 | 0.0675(2) | 0.79701(10) | 0.15748(18) | 0.0539(6) |
| H4 | 0.1209 | 0.8353 | 0.1820 | 0.081* |
| O5 | 0.3169(2) | 0.87250(10) | 0.26028(16) | 0.0478(5) |
| O6 | 0.6286(2) | 0.87039(9) | 0.37013(15) | 0.0422(5) |
| O7 | 1.1846(2) | 0.80685(10) | 0.52927(17) | 0.0554(6) |
| O8 | 1.2827(2) | 0.65493(10) | 0.52644(17) | 0.0531(6) |
| H8 | 1.3311 | 0.6941 | 0.5529 | 0.080* |
| C1’ | 0.8013(3) | 0.71289(14) | 0.4003(2) | 0.0342(6) |
| C2’ | 0.9090(3) | 0.77182(15) | 0.4446(2) | 0.0393(7) |
| H2’ | 0.8721 | 0.8241 | 0.4457 | 0.047* |
| C3’ | 1.0688(3) | 0.75358(15) | 0.4867(2) | 0.0385(7) |
| C4’ | 1.1240(3) | 0.67539(15) | 0.4881(2) | 0.0378(7) |
| C5’ | 1.0176(3) | 0.61722(15) | 0.4478(2) | 0.0476(8) |
| H5’ | 1.0530 | 0.5647 | 0.4504 | 0.057* |
| C6’ | 0.8589(3) | 0.63525(15) | 0.4034(2) | 0.0438(7) |
| H6’ | 0.7893 | 0.5949 | 0.3752 | 0.053* |
| C2 | 0.6344(3) | 0.73097(14) | 0.3490(2) | 0.0343(6) |
| C3 | 0.5555(3) | 0.80169(14) | 0.3315(2) | 0.0343(6) |
| C4 | 0.3905(3) | 0.80718(14) | 0.2762(2) | 0.0367(7) |
| C5 | 0.1549(3) | 0.72954(15) | 0.1825(2) | 0.0376(7) |
| C6 | 0.0870(3) | 0.65860(15) | 0.1502(2) | 0.0437(7) |
| H6 | −0.0169 | 0.6569 | 0.1108 | 0.052* |
| C7 | 0.1727(3) | 0.58862(15) | 0.1761(2) | 0.0400(7) |
| C8 | 0.3295(3) | 0.59027(13) | 0.2321(2) | 0.0350(6) |
| C9 | 0.3981(3) | 0.66317(14) | 0.2619(2) | 0.0325(6) |
| C10 | 0.3141(3) | 0.73404(13) | 0.2397(2) | 0.0332(6) |
| C16 | 0.4285(4) | 0.49738(16) | 0.3677(2) | 0.0574(9) |
| H16B | 0.5130 | 0.4570 | 0.3782 | 0.086* |
| H16A | 0.3213 | 0.4772 | 0.3895 | 0.086* |
| H16C | 0.4588 | 0.5424 | 0.4136 | 0.086* |
| C17 | 0.7073(4) | 0.91556(16) | 0.2842(3) | 0.0623(9) |
| H17C | 0.6266 | 0.9259 | 0.2233 | 0.093* |
| H17A | 0.8006 | 0.8862 | 0.2563 | 0.093* |
| H17B | 0.7474 | 0.9648 | 0.3156 | 0.093* |
| C18 | 1.1472(4) | 0.88914(15) | 0.5160(3) | 0.0551(8) |
| H18C | 1.1156 | 0.8998 | 0.4384 | 0.083* |
| H18A | 1.2452 | 0.9198 | 0.5379 | 0.083* |
| H18B | 1.0558 | 0.9031 | 0.5628 | 0.083* |
Source of material
The title compound C18H16O8 was isolated using high speed countercurrent chromatography (HSCCC). Following our program to isolate components from the Atacama Desert Flora, Northern Chile [1], [2], [3], [4], dried aerial parts of Parastrephia quadrangularis (1622 g) collected in april 2015 in El Tatio, were defatted with hexane (3 liters, 3 times in the dark, 24 h each time) and 54.82 g were obtained after evaporation of the solvent. Then the plant material was extracted with ethyl acetate (3 liters, 3 times in the dark, 24 Hs each time. After evaporation of the solvent under vacuo at 35 oC, 485 g of a dark gummy extract was obtained. A portion of the extract (0.5 g) was filtered and submitted to a HSCCC centrifuge (Quattro MK-7, Bridgend, UK) for the separation of its components. The solvent system selected was the isocratic two-phase non aqueous solvent system: n-hexane: ethyl acetate: methanol: water 3:7:5:5 v/v/v provided the better K values for all major compounds (0.5 < K < 1.3). This system was previously used for the separation of terpenes [4]. After equilibration of the solvent system in a separatory funnel, the upper and lower working phases were separated and degassed in an ultrasonic bath for 15 min before use. The sample was prepared by dissolving 500 mg of exudate from P. quadrangularis in 5.0 mL of each phase of the solvent system, filtered and loaded into an injection valve (Rheodyne model 5010A) equipped with a 8 mL loop. The preparative coil (116 mL) was filled with the upper stationary phase and the apparatus was rotated at 850 rpm. The mobile lower phase was then pumped in a head-to-tail direction (H-T) at a flow rate of 5 mL/minute. After the mobile phase front emerged and the hydrodynamic equilibrium was established in the column, the percentage of the retention of the stationary phase (60%) was recorded. Then the sample was injected thorough the injection valve at a flow rate of 5 mL-minute. The fractions eluted were collected with the fraction collector (5 mL each) and analyzed by TLC (F254 Silica gel plates, developed with hexane : EtOAc, 1 : 1 v/v, and spots visualized by spraying with vanillin : sulfuric acid 2% in ethanol and heating. CCC rotation was interrupted in tube 70 and the coil content was collected (“wash-off”), originating 95 fractions of 6 mL each. After re-purification by sephadex LH 20 (solvent methanol), HSCCC fractions 12–18 afforded 11-p-coumaroyl-tremetone [5], (55 mg) fractions 23–29 umbelliferone [6] (12 mg) and fractions 35–38 the title compound (5, 7, 4′ trihydroxy-3,8,3′ trymethoxyflavone, 12 mg) for which NMR data are consistent with literature [7], [8], [9]. Recrystallization from ethyl acetate at −20° C yielded yellow crystals (5 mg), m.p. 265–267 °C. The molecular weight was determined by orbitrap ESI-MS/MS with a mass spectrometer (Q-exactive Focus, Bremen, Germany) [M-H]−: 359.0771, calcd. for C18H17O8−: 359.0772. 1H-NMR (Bruker Avance 300 MHz, DMSO-d6) δ ppm: 7.65(1H, d, J = 1.4 Hz, H-2′), 7.55(1H, dd, J = 1.4, 8.4 Hz, H-6′), 6.97(1H, d, J = 8.4 Hz, H-5′), 6.43(1H, s, H-6), 3.90(3H, s, OCH3), 3.93(3H, s, OCH3), 3.86(3H, s, OCH3). 13C-NMR (Bruker Avance 300 MHz, DMSO-d6) δ ppm: 147.92 (C-2), 137.23 (C-3), 177.35 (C-4), 162.54 (C-5), 99.35 (C-6), 165.74 (C-7), 163.2 (C-8), 158.2 (C-9), 104.4 (C-10), 124.13 (C-1), 116.06 (C-2′), 146.23 (C-3′), 148.75 (C-4′), 116.23 (C-5′), 121.66 (C-6′), 56.92 (O-CH3), 56.90 (O-CH3), 56.95 (O-CH3).
Experimental details
H atoms were located in the difference Fourier map, but refined with fixed individual displacement parameters, using a riding mode with C—H distances of 0.93 Å (for aromatic rings), 0.96 Å (for CH3), with Uiso(H) values of 1.2Ueq(C) (for CH in aromatic), and 1.5Ueq(C) (for methyl group), O—H distances are 0.82 Å with Uiso(H) values of 1.5Ueq(O).
Discussion
The core system of the title compound is planar (r.m.s. deviation 0.072 Å), excluding the methyl groups C16 and C17. The molecular structure is stabilized by an intramolecular hydrogen bond, O4—H4⋯O5. In the crystal packing all hydroxyl groups participate as donor and acceptor of intermolecular hydrogen bonds interactions. In total different set-graphs motifs such as chains and rings are present [14]. The packing also features π–π stacking interactions between benzene rings [centroid–centroid distance = 3.701(2) Å]. All distances and angles are in the normal range.
Acknowledgements
The authors thank FONDECYT (Chile) (Grant 1140178) for financial support. IB Thanks to Fondequip (EQM13–0021).
References
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©2017 Iván Brito et al., published by De Gruyter.
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