organic compounds\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

Journal logoCRYSTALLOGRAPHIC
COMMUNICATIONS
ISSN: 2056-9890

2-Hydr­­oxy-1,6,7,8-tetra­meth­­oxy-3-methyl­anthra­quinone

aCollege of Light Industry and Food Sciences, South China University of Technology, Guangzhou 510641, People's Republic of China
*Correspondence e-mail: lfshjyu@scut.edu.cn

(Received 15 November 2007; accepted 20 December 2007; online 4 January 2008)

The title compound, C19H18O7, also known as chrysoobtusin, was isolated from Cassia tora L. (Leguminosae). The anthraquinone ring system is almost planar, the dihedral angle between the two benzene rings being 4.27 (4)°. The structure is stabilized by intra- and inter­molecular O—H⋯O and C—H⋯O hydrogen bonds, and by weak ππ stacking inter­actions along the b axis, with a centroid–centroid distance between related benzene rings of 3.800 (4) Å.

Related literature

For related literature, see: Boonnak et al. (2005[Boonnak, N., Chantrapromma, S., Fun, H.-K., Anjum, S., Ali, S., Atta-ur-Rahman & Karalai, C. (2005). Acta Cryst. E61, o410-o412.]); Hao et al. (1995[Hao, N. J., Huang, M. P. & Lee, H. (1995). Mutat. Res. 328, 183-191.]); Jia et al. (2007[Jia, Z. B., Tao, F., Guo, L., Tao, G. L. & Ding, X. L. (2007). LWT Food Sci. Technol. 40, 1072-1077.]); Ng et al. (2005[Ng, S.-L., Razak, I. A., Fun, H.-K., Boonsri, S., Chantrapromma, S. & Prawat, U. (2005). Acta Cryst. E61, o3656-o3658.]); Patil et al. (2004[Patil, U. K., Saraf, S. & Dixit, V. K. (2004). J. Ethnopharmacol. 90, 249-252.]); Wu & Yen (2004[Wu, C. H. & Yen, G. C. (2004). Life Sci. 76, 85-101.]); Allen et al. (1987[Allen, F. H., Kennard, O., Watson, D. G., Brammer, L., Orpen, A. G. & Taylor, R. (1987). J. Chem. Soc. Perkin Trans. 2, pp. S1-19.]).

[Scheme 1]

Experimental

Crystal data
  • C19H18O7

  • Mr = 358.33

  • Monoclinic, P 21 /n

  • a = 12.2960 (3) Å

  • b = 7.8545 (2) Å

  • c = 18.3361 (5) Å

  • β = 106.581 (2)°

  • V = 1697.24 (8) Å3

  • Z = 4

  • Mo Kα radiation

  • μ = 0.11 mm−1

  • T = 296 (2) K

  • 0.30 × 0.28 × 0.26 mm

Data collection
  • Bruker APEXII area-detector diffractometer

  • Absorption correction: none

  • 13295 measured reflections

  • 3871 independent reflections

  • 2527 reflections with I > 2σ(I)

  • Rint = 0.032

Refinement
  • R[F2 > 2σ(F2)] = 0.046

  • wR(F2) = 0.133

  • S = 1.02

  • 3871 reflections

  • 241 parameters

  • H-atom parameters constrained

  • Δρmax = 0.19 e Å−3

  • Δρmin = −0.21 e Å−3

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
C18—H18A⋯O4 0.96 2.53 3.074 (3) 116
C17—H17A⋯O4 0.96 2.60 3.046 (3) 109
C16—H16A⋯O1 0.96 2.50 3.049 (3) 116
O7—H7⋯O6 0.82 2.19 2.6482 (17) 116
O7—H7⋯O3i 0.82 2.02 2.7221 (16) 144
Symmetry code: (i) [-x+{\script{1\over 2}}, y-{\script{1\over 2}}, -z+{\script{1\over 2}}].

Data collection: APEX2 (Bruker, 2004[Bruker (2004). APEX2 (Version 7.23A), SAINT (Version 7.23A) and SHELXTL (Version 6.10). Bruker AXS Inc., Madison, Wisconsin, USA.]); cell refinement: SAINT (Bruker, 2004[Bruker (2004). APEX2 (Version 7.23A), SAINT (Version 7.23A) and SHELXTL (Version 6.10). Bruker AXS Inc., Madison, Wisconsin, USA.]); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997[Sheldrick, G. M. (1997). SHELXS97 and SHELXL97. University of Göttingen, Germany.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997[Sheldrick, G. M. (1997). SHELXS97 and SHELXL97. University of Göttingen, Germany.]); molecular graphics: SHELXTL (Bruker, 2004[Bruker (2004). APEX2 (Version 7.23A), SAINT (Version 7.23A) and SHELXTL (Version 6.10). Bruker AXS Inc., Madison, Wisconsin, USA.]); software used to prepare material for publication: SHELXTL.

Supporting information


Comment top

Anthraquinone derivatives extracted from the seeds of Cassia tora L. (most common familiar name in China: Juemingzi) have been used traditionally to improve visual acuity. Recent studies have demonstrated that they have multiple pharmacological actions such as antimicrobial, diuretic, antidiarrhoic, antioxidant, antihepatotoxic and antimutagenic activities (Wu & Yen, 2004). One component found in Cassia tora L., 2-hydroxy-1,6,7,8-tetramethoxy-3-methylanthraquinone, is known as chrysoobusin and exhibits a variety of potent biological effects such as suppression of mutagenicity of mycotoxins (Hao et al., 1995), antioxidant activity (Jia et al., 2007) and hypolipidemic activity (Patil et al., 2004). We report here the structure of the title compound.

In the title compound (Fig. 1), the C—C bond lengths show normal values (Allen et al., 1987), and the C—O and C=O bond lengths are comparable to those observed in similar structures (Ng et al., 2005; Boonnak et al., 2005). The anthraquinone ring system is substantially planar, the dihedral angle between the two benzene rings being 4.27 (4)°. The molecules are self-assembled by intra- and intermolecular C—H···O and O—H···.O hydrogen bonding interactions (Table 1) into a superamolecular network. The crystal structure is further stabilized by weak π-π stacking interactions along the b axis (Fig. 2) occurring between centrosymmetrically related anthraquinone ring systems. The centroid-to-centriod distances between related benzene rings of the stacked molecules is 3.800 (4) Å.

Related literature top

For related literature, see: Boonnak et al. (2005); Hao et al. (1995); Jia et al. (2007); Ng et al. (2005); Patil et al. (2004); Wu & Yen (2004); Allen et al. (1987); Sheldrick (1996).

Experimental top

The seeds of Cassia tora L. (800 g) were shattered to powder (about 30 mesh) and extracted with 60% ethanol (3000 ml) for 40 min by microwave irradiation at 333 K. The extraction procedure was repeated three times. The extracts were combined and evaporated to dryness under reduced pressure at 333 K, the residue was redissolved in water (600 ml) and was added 400 ml light petroleum to remove low-polar substaces three times. Then the enriched extracts were extracted with chloroform four times (500 ml for each time), the chlorofrom solution were combined and evaporated to dryness under reduced pressure at 333 K, 4.52 g crude extracts was obtained. The crude extracts were separated with n-hexane-ethyl acetate-methanol-water (11: 90: 10: 10, v/v) using high-speed counter-current chromatography (HSCCC) to obtain 2-hydroxy-1,6,7,8-tetramethoxy-3-methylanthraquinone (yield 46.2 mg). Single crystals suitable for X-ray analysis were obtained by slow evaporation of a methanol solution.

Refinement top

All H atoms were placed at calculated positions and were treated as riding on the parent C atoms with C—H = 0.93–0.97 and O—H = 0.82 Å, and with Uiso(H) = 1.2 or 1.5 Ueq(C, O).

Computing details top

Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT (Bruker, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 2004); software used to prepare material for publication: SHELXTL (Bruker, 2004).

Figures top
[Figure 1] Fig. 1. The molecular structure of the title compound showing the atomic-numbering scheme and displacement ellipsoids drawn at the 50% probability level.
[Figure 2] Fig. 2. The molecular packing of the title compound showing the intra- and intermolecular hydrogen bonding interactions as broken lines.
2-Hydroxy-1,6,7,8-tetramethoxy-3-methylanthraquinone top
Crystal data top
C19H18O7F(000) = 752
Mr = 358.33Dx = 1.402 Mg m3
Monoclinic, P21/nMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ynCell parameters from 3645 reflections
a = 12.2960 (3) Åθ = 1.4–28.0°
b = 7.8545 (2) ŵ = 0.11 mm1
c = 18.3361 (5) ÅT = 296 K
β = 106.581 (2)°Block, yellow
V = 1697.24 (8) Å30.30 × 0.28 × 0.26 mm
Z = 4
Data collection top
Bruker APEXII area-detector
diffractometer
2527 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.032
Graphite monochromatorθmax = 27.5°, θmin = 1.8°
f and ω scansh = 1515
13295 measured reflectionsk = 1010
3871 independent reflectionsl = 2323
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.046Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.133H-atom parameters constrained
S = 1.02 w = 1/[σ2(Fo2) + (0.0598P)2 + 0.2883P]
where P = (Fo2 + 2Fc2)/3
3871 reflections(Δ/σ)max < 0.001
241 parametersΔρmax = 0.19 e Å3
0 restraintsΔρmin = 0.21 e Å3
Crystal data top
C19H18O7V = 1697.24 (8) Å3
Mr = 358.33Z = 4
Monoclinic, P21/nMo Kα radiation
a = 12.2960 (3) ŵ = 0.11 mm1
b = 7.8545 (2) ÅT = 296 K
c = 18.3361 (5) Å0.30 × 0.28 × 0.26 mm
β = 106.581 (2)°
Data collection top
Bruker APEXII area-detector
diffractometer
2527 reflections with I > 2σ(I)
13295 measured reflectionsRint = 0.032
3871 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0460 restraints
wR(F2) = 0.133H-atom parameters constrained
S = 1.02Δρmax = 0.19 e Å3
3871 reflectionsΔρmin = 0.21 e Å3
241 parameters
Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
C10.12772 (16)0.3847 (2)0.08053 (10)0.0478 (4)
C20.23670 (15)0.3514 (2)0.03234 (10)0.0479 (4)
C30.25066 (14)0.2624 (2)0.03525 (9)0.0417 (4)
C40.15663 (13)0.2073 (2)0.05800 (9)0.0391 (4)
C50.04861 (13)0.2443 (2)0.00932 (9)0.0394 (4)
C60.03506 (15)0.3313 (2)0.05891 (9)0.0452 (4)
H60.03760.35360.09020.054*
C70.05610 (14)0.1888 (2)0.02762 (9)0.0419 (4)
C80.04420 (13)0.10489 (19)0.10100 (9)0.0391 (4)
C90.06335 (13)0.07377 (19)0.15239 (9)0.0385 (4)
C100.16909 (14)0.1101 (2)0.12996 (9)0.0420 (4)
C110.06680 (13)0.0001 (2)0.22235 (9)0.0404 (4)
C120.03346 (14)0.0496 (2)0.23820 (9)0.0447 (4)
C130.14001 (14)0.0222 (2)0.18680 (9)0.0459 (4)
C140.14247 (14)0.0570 (2)0.11918 (9)0.0444 (4)
H140.21240.07930.08440.053*
C150.01444 (17)0.4980 (3)0.19883 (11)0.0645 (5)
H15A0.02230.39130.21570.097*
H15B0.02360.56000.24180.097*
H15C0.03110.56340.17440.097*
C160.3571 (2)0.5740 (3)0.04686 (16)0.0795 (7)
H16A0.29510.63700.07940.119*
H16B0.42460.59460.06190.119*
H16C0.36900.60980.00490.119*
C170.41092 (17)0.0855 (3)0.06199 (13)0.0682 (6)
H17A0.36520.01080.06660.102*
H17B0.48550.07290.09670.102*
H17C0.41630.09200.01090.102*
C180.21311 (19)0.1135 (3)0.32189 (12)0.0727 (6)
H18A0.24430.18580.29070.109*
H18B0.27230.07900.36600.109*
H18C0.15590.17450.33750.109*
C190.24641 (16)0.0758 (3)0.20556 (12)0.0666 (6)
H19A0.31140.03110.16800.100*
H19B0.24500.03270.25480.100*
H19C0.25070.19780.20580.100*
O10.12327 (11)0.46722 (18)0.14620 (7)0.0641 (4)
O20.33123 (11)0.39758 (17)0.05315 (8)0.0617 (4)
O30.36000 (9)0.23760 (15)0.07962 (6)0.0495 (3)
O40.26068 (10)0.05769 (19)0.16791 (7)0.0642 (4)
O50.14949 (10)0.21417 (18)0.01744 (7)0.0581 (4)
O60.16389 (10)0.03329 (16)0.27947 (6)0.0510 (3)
O70.02886 (10)0.12633 (19)0.30522 (7)0.0599 (4)
H70.03760.14340.32910.090*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C10.0551 (11)0.0446 (9)0.0446 (9)0.0084 (8)0.0161 (8)0.0035 (8)
C20.0478 (10)0.0460 (9)0.0522 (10)0.0032 (8)0.0180 (8)0.0028 (8)
C30.0395 (9)0.0421 (9)0.0407 (9)0.0039 (7)0.0069 (7)0.0082 (7)
C40.0396 (9)0.0387 (8)0.0363 (8)0.0037 (7)0.0064 (7)0.0053 (7)
C50.0412 (9)0.0371 (8)0.0367 (8)0.0034 (7)0.0061 (7)0.0039 (7)
C60.0450 (9)0.0420 (9)0.0455 (9)0.0075 (7)0.0080 (7)0.0007 (8)
C70.0409 (9)0.0399 (9)0.0401 (8)0.0051 (7)0.0038 (7)0.0022 (7)
C80.0399 (9)0.0369 (8)0.0368 (8)0.0029 (7)0.0047 (7)0.0036 (7)
C90.0396 (8)0.0349 (8)0.0376 (8)0.0017 (7)0.0056 (7)0.0034 (7)
C100.0388 (9)0.0431 (9)0.0392 (9)0.0036 (7)0.0032 (7)0.0049 (7)
C110.0386 (8)0.0389 (8)0.0379 (8)0.0025 (7)0.0017 (7)0.0031 (7)
C120.0474 (10)0.0459 (9)0.0379 (8)0.0022 (8)0.0078 (7)0.0005 (7)
C130.0426 (9)0.0484 (10)0.0450 (9)0.0006 (8)0.0098 (7)0.0017 (8)
C140.0368 (8)0.0475 (9)0.0435 (9)0.0043 (7)0.0026 (7)0.0019 (8)
C150.0741 (14)0.0684 (13)0.0482 (10)0.0172 (11)0.0129 (10)0.0118 (10)
C160.0717 (15)0.0681 (14)0.1065 (19)0.0097 (12)0.0382 (14)0.0046 (14)
C170.0536 (11)0.0765 (14)0.0700 (13)0.0212 (10)0.0104 (10)0.0125 (11)
C180.0665 (13)0.0868 (16)0.0526 (11)0.0165 (12)0.0026 (10)0.0160 (11)
C190.0477 (11)0.0890 (15)0.0636 (12)0.0002 (10)0.0165 (9)0.0115 (11)
O10.0621 (8)0.0764 (9)0.0543 (8)0.0081 (7)0.0177 (7)0.0207 (7)
O20.0554 (8)0.0657 (9)0.0712 (9)0.0024 (7)0.0298 (7)0.0041 (7)
O30.0375 (6)0.0581 (7)0.0487 (7)0.0028 (5)0.0056 (5)0.0093 (6)
O40.0424 (7)0.0934 (11)0.0526 (7)0.0150 (7)0.0069 (6)0.0189 (7)
O50.0399 (7)0.0773 (9)0.0495 (7)0.0038 (6)0.0005 (6)0.0141 (7)
O60.0447 (7)0.0585 (7)0.0411 (6)0.0002 (6)0.0016 (5)0.0051 (6)
O70.0489 (7)0.0822 (10)0.0461 (7)0.0018 (7)0.0096 (6)0.0156 (7)
Geometric parameters (Å, º) top
C1—O11.355 (2)C13—C141.380 (2)
C1—C61.374 (2)C13—C191.505 (2)
C1—C21.403 (2)C14—H140.9300
C2—O21.372 (2)C15—O11.429 (2)
C2—C31.390 (2)C15—H15A0.9600
C3—O31.3723 (19)C15—H15B0.9600
C3—C41.405 (2)C15—H15C0.9600
C4—C51.403 (2)C16—O21.419 (2)
C4—C101.494 (2)C16—H16A0.9600
C5—C61.393 (2)C16—H16B0.9600
C5—C71.485 (2)C16—H16C0.9600
C6—H60.9300C17—O31.428 (2)
C7—O51.2245 (19)C17—H17A0.9600
C7—C81.468 (2)C17—H17B0.9600
C8—C141.394 (2)C17—H17C0.9600
C8—C91.409 (2)C18—O61.425 (2)
C9—C111.397 (2)C18—H18A0.9600
C9—C101.499 (2)C18—H18B0.9600
C10—O41.2144 (19)C18—H18C0.9600
C11—O61.3699 (18)C19—H19A0.9600
C11—C121.400 (2)C19—H19B0.9600
C12—O71.355 (2)C19—H19C0.9600
C12—C131.395 (2)O7—H70.8200
O1—C1—C6125.14 (16)C13—C14—C8122.57 (15)
O1—C1—C2115.97 (16)C13—C14—H14118.7
C6—C1—C2118.88 (16)C8—C14—H14118.7
O2—C2—C3118.82 (16)O1—C15—H15A109.5
O2—C2—C1120.56 (16)O1—C15—H15B109.5
C3—C2—C1120.52 (16)H15A—C15—H15B109.5
O3—C3—C2116.80 (15)O1—C15—H15C109.5
O3—C3—C4122.02 (15)H15A—C15—H15C109.5
C2—C3—C4121.13 (15)H15B—C15—H15C109.5
C5—C4—C3117.20 (15)O2—C16—H16A109.5
C5—C4—C10120.50 (14)O2—C16—H16B109.5
C3—C4—C10122.29 (14)H16A—C16—H16B109.5
C6—C5—C4121.45 (15)O2—C16—H16C109.5
C6—C5—C7117.22 (14)H16A—C16—H16C109.5
C4—C5—C7121.32 (15)H16B—C16—H16C109.5
C1—C6—C5120.80 (16)O3—C17—H17A109.5
C1—C6—H6119.6O3—C17—H17B109.5
C5—C6—H6119.6H17A—C17—H17B109.5
O5—C7—C8121.37 (16)O3—C17—H17C109.5
O5—C7—C5120.42 (15)H17A—C17—H17C109.5
C8—C7—C5118.21 (14)H17B—C17—H17C109.5
C14—C8—C9120.37 (15)O6—C18—H18A109.5
C14—C8—C7118.30 (14)O6—C18—H18B109.5
C9—C8—C7121.33 (15)H18A—C18—H18B109.5
C11—C9—C8117.57 (15)O6—C18—H18C109.5
C11—C9—C10121.97 (14)H18A—C18—H18C109.5
C8—C9—C10120.37 (14)H18B—C18—H18C109.5
O4—C10—C4121.60 (15)C13—C19—H19A109.5
O4—C10—C9120.89 (15)C13—C19—H19B109.5
C4—C10—C9117.48 (13)H19A—C19—H19B109.5
O6—C11—C9124.92 (15)C13—C19—H19C109.5
O6—C11—C12114.54 (14)H19A—C19—H19C109.5
C9—C11—C12120.53 (14)H19B—C19—H19C109.5
O7—C12—C13118.00 (15)C1—O1—C15118.27 (15)
O7—C12—C11120.03 (14)C2—O2—C16115.05 (15)
C13—C12—C11121.98 (15)C3—O3—C17113.79 (13)
C14—C13—C12116.89 (15)C11—O6—C18113.88 (14)
C14—C13—C19122.28 (16)C12—O7—H7109.5
C12—C13—C19120.83 (16)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C18—H18A···O40.962.533.074 (3)116
C17—H17A···O40.962.603.046 (3)109
C16—H16A···O10.962.503.049 (3)116
O7—H7···O60.822.192.6482 (17)116
O7—H7···O3i0.822.022.7221 (16)144
Symmetry code: (i) x+1/2, y1/2, z+1/2.

Experimental details

Crystal data
Chemical formulaC19H18O7
Mr358.33
Crystal system, space groupMonoclinic, P21/n
Temperature (K)296
a, b, c (Å)12.2960 (3), 7.8545 (2), 18.3361 (5)
β (°) 106.581 (2)
V3)1697.24 (8)
Z4
Radiation typeMo Kα
µ (mm1)0.11
Crystal size (mm)0.30 × 0.28 × 0.26
Data collection
DiffractometerBruker APEXII area-detector
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
13295, 3871, 2527
Rint0.032
(sin θ/λ)max1)0.650
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.046, 0.133, 1.02
No. of reflections3871
No. of parameters241
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.19, 0.21

Computer programs: APEX2 (Bruker, 2004), SAINT (Bruker, 2004), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), SHELXTL (Bruker, 2004).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C18—H18A···O40.962.533.074 (3)116.2
C17—H17A···O40.962.603.046 (3)108.7
C16—H16A···O10.962.503.049 (3)116.0
O7—H7···O60.822.192.6482 (17)115.5
O7—H7···O3i0.822.022.7221 (16)144.1
Symmetry code: (i) x+1/2, y1/2, z+1/2.
 

Acknowledgements

The authors acknowledge the Ministry of Science and Technology of China (fund No. 2006BAD27B03) for financial support, and South China University of Technology and South China Normal University for supporting this work.

References

First citationAllen, F. H., Kennard, O., Watson, D. G., Brammer, L., Orpen, A. G. & Taylor, R. (1987). J. Chem. Soc. Perkin Trans. 2, pp. S1–19.  CrossRef Web of Science Google Scholar
First citationBoonnak, N., Chantrapromma, S., Fun, H.-K., Anjum, S., Ali, S., Atta-ur-Rahman & Karalai, C. (2005). Acta Cryst. E61, o410–o412.  Google Scholar
First citationBruker (2004). APEX2 (Version 7.23A), SAINT (Version 7.23A) and SHELXTL (Version 6.10). Bruker AXS Inc., Madison, Wisconsin, USA.  Google Scholar
First citationHao, N. J., Huang, M. P. & Lee, H. (1995). Mutat. Res. 328, 183–191.  CrossRef CAS PubMed Web of Science Google Scholar
First citationJia, Z. B., Tao, F., Guo, L., Tao, G. L. & Ding, X. L. (2007). LWT Food Sci. Technol. 40, 1072–1077.  Google Scholar
First citationNg, S.-L., Razak, I. A., Fun, H.-K., Boonsri, S., Chantrapromma, S. & Prawat, U. (2005). Acta Cryst. E61, o3656–o3658.  Web of Science CSD CrossRef IUCr Journals Google Scholar
First citationPatil, U. K., Saraf, S. & Dixit, V. K. (2004). J. Ethnopharmacol. 90, 249–252.  Web of Science CrossRef PubMed Google Scholar
First citationSheldrick, G. M. (1997). SHELXS97 and SHELXL97. University of Göttingen, Germany.  Google Scholar
First citationWu, C. H. & Yen, G. C. (2004). Life Sci. 76, 85–101.  Web of Science CrossRef PubMed CAS Google Scholar

This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.

Journal logoCRYSTALLOGRAPHIC
COMMUNICATIONS
ISSN: 2056-9890
Follow Acta Cryst. E
Sign up for e-alerts
Follow Acta Cryst. on Twitter
Follow us on facebook
Sign up for RSS feeds