(E)-2,3-Bis(4-methoxy­phen­yl)acrylic acid

Ruan, B.; Yang, Y.; Zhu, Z.; Lv, P.; Zhu, H.

doi:10.1107/S1600536809011751

organic compounds

CRYSTALLOGRAPHIC
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ISSN: 2056-9890

Volume 65| Part 5| May 2009| Page o944

doi:10.1107/S1600536809011751

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(E)-2,3-Bis(4-methoxyphenyl)acrylic acid

Banfeng Ruan,^a Ying Yang,^a Zhenwei Zhu,^a Pengcheng Lv ^a and Hailiang Zhu ^a ^*

^aState Key Laboratory of Pharmaceutical Biotechnology, Nanjing University, Nanjing 210093, People's Republic of China
^*Correspondence e-mail: zhuhl@nju.edu.cn

(Received 25 March 2009; accepted 30 March 2009; online 2 April 2009)

In the title molecule, C₁₇H₁₆O₄, the angle between the aromatic ring planes is 69.1 (6)°. The crystal structure is stabilized by intermolecular O—H⋯O hydrogen bonds; molecules related by a centre of symmetry are linked to form inversion dimers.

Related literature

For the biological properties and synthesis of resveratrol (trans-3,4′,5-trihydroxystilbene) and its derivatives, see: Huang, Ruan et al. (2007 ); Huang et al. (2008 ); Jang et al. (1997 ); Ruan et al. (2006 ); Schulze et al. (2005 ); Shi et al. (2005 ). For related crystal structures, see: Huang, Li et al. (2007 ); Stomberg et al. (2001 ).

Experimental

Crystal data

C₁₇H₁₆O₄
M_r = 284.30
Triclinic, $[P \overline 1]$
a = 5.8690 (12) Å
b = 9.1480 (18) Å
c = 13.992 (3) Å
α = 83.65 (3)°
β = 85.43 (3)°
γ = 80.92 (3)°
V = 735.8 (3) Å³
Z = 2
Mo Kα radiation
μ = 0.09 mm⁻¹
T = 298 K
0.30 × 0.20 × 0.10 mm

Data collection

Enraf–Nonius CAD-4 diffractometer
Absorption correction: ψ scan (North et al., 1968 ) T_min = 0.973, T_max = 0.991
3196 measured reflections
2895 independent reflections
1779 reflections with I > 2σ(I)
R_int = 0.027

Refinement

R[F² > 2σ(F²)] = 0.056
wR(F²) = 0.151
S = 1.08
2895 reflections
194 parameters
H-atom parameters constrained
Δρ_max = 0.18 e Å⁻³
Δρ_min = −0.17 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O3—H3⋯O2ⁱ	0.82	1.80	2.608 (2)	169
Symmetry code: (i) -x+3, -y+2, -z+1.

Data collection: CAD-4 Software (Enraf–Nonius, 1989 ); cell refinement: CAD-4 Software; data reduction: XCAD4 (Harms & Wocadlo, 1995 ); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL.

Supporting information

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536809011751/wn2320sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536809011751/wn2320Isup2.hkl

checkCIF report

Comment top

Resveratrol (trans-3, 4',5-trihydroxystilbene) and its derivatives have attracted much attention since it was first isolated in 1939, because of their physiological properties and potential therapeutic values (Schulze et al., 2005; Jang et al., 1997). In our laboratory, we have synthesized two series of resveratrol derivatives (Ruan et al., 2006; Huang et al., 2007). As part of an extensive structure-activity relationship (SAR) study on resveratrol derivatives, another series of analogues of resveratrol has been synthesized. One of them, namely the title compound, was obtained as single crystals and its crystal structure determined to establish its configuration.

The crystal structure demonstrated that it had the E configuration (Fig. 1). All bond lengths are within normal ranges and very similar to those in related crystal structures (Stomberg et al., 2001). The torsion angles C5—C8—C10—C11 and C9—C8—C10—C11 are 5.9 (4)° and -176.6 (2)°, respectively. The angle between the aromatic ring planes is 69.1 (6)°. In the crystal structure, molecules related by a centre of symmetry are linked to form dimers via intermolecular O—H—O hydrogen bonds (Table 1 and Fig. 2).

Related literature top

For the biological properties and synthesis of resveratrol (trans-3, 4',5-trihydroxystilbene) and its derivatives, see: Huang, Ruan et al. (2007, 2008); Jang et al. (1997); Ruan et al. (2006); Schulze et al. (2005); Shi et al. (2008). For related crystal structures, see: Huang, Li et al. (2007; Stomberg et al. (2001).

Experimental top

2-(4-Methoxyphenyl)acetic acid (1.66 g, 0.01 mol), 4-methoxybenzaldehyde (1.36 g, 0.01 mol) and acetic anhydride (15 ml) were added to a three-necked flask in an icewater bath with stirring. Triethylamine (5 ml) was added dropwise into this solution and the mixture was allowed to react at 100°C for 12 h. After cooling to room temperature, the mixture was slowly poured into 50 ml 10% NaOH solution, yielding a white precipitate. This was collected by vacuum filtration, washed with a large amount of water and dried in air. Colorless single crystals were obtained after a week upon evaporation of a solution of the reaction product in a mixture of ethyl acetate (10 ml) and petroleum ether (5 ml).

Computing details top

Data collection: CAD-4 Software (Enraf–Nonius, 1989); cell refinement: CAD-4 Software (Enraf–Nonius, 1989); data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top

	Fig. 1. The molecular structure of the title compound, showing 30% probability displacement ellipsoids and the atom-numbering scheme. All H atoms have been omitted.
	Fig. 2. A view of the hydrogen-bonded dimer of the title compound. Dashed lines indicate hydrogen bonds. [Symmetry code: (A) -x + 3, -y + 2, -z + 1]

(E)-2,3-Bis(4-methoxyphenyl)acrylic acid top

Crystal data top

C₁₇H₁₆O₄	Z = 2
M_r = 284.30	F(000) = 300
Triclinic, P1	D_x = 1.283 Mg m⁻³
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 5.8690 (12) Å	Cell parameters from 1625 reflections
b = 9.1480 (18) Å	θ = 2.2–24.8°
c = 13.992 (3) Å	µ = 0.09 mm⁻¹
α = 83.65 (3)°	T = 298 K
β = 85.43 (3)°	Block, colorless
γ = 80.92 (3)°	0.30 × 0.20 × 0.10 mm
V = 735.8 (3) Å³

Data collection top

Enraf–Nonius CAD-4 diffractometer	2895 independent reflections
Radiation source: fine-focus sealed tube	1779 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.027
ω/2θ scans	θ_max = 26.0°, θ_min = 1.5°
Absorption correction: ψ scan (North et al., 1968)	h = 0→7
T_min = 0.973, T_max = 0.991	k = −11→11
3196 measured reflections	l = −17→17

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.056	H-atom parameters constrained
wR(F²) = 0.151	w = 1/[σ²(F_o²) + (0.0675P)² + 0.024P] where P = (F_o² + 2F_c²)/3
S = 1.08	(Δ/σ)_max < 0.001
2895 reflections	Δρ_max = 0.18 e Å⁻³
194 parameters	Δρ_min = −0.17 e Å⁻³
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.044 (7)

Crystal data top

C₁₇H₁₆O₄	γ = 80.92 (3)°
M_r = 284.30	V = 735.8 (3) Å³
Triclinic, P1	Z = 2
a = 5.8690 (12) Å	Mo Kα radiation
b = 9.1480 (18) Å	µ = 0.09 mm⁻¹
c = 13.992 (3) Å	T = 298 K
α = 83.65 (3)°	0.30 × 0.20 × 0.10 mm
β = 85.43 (3)°

Data collection top

Enraf–Nonius CAD-4 diffractometer	2895 independent reflections
Absorption correction: ψ scan (North et al., 1968)	1779 reflections with I > 2σ(I)
T_min = 0.973, T_max = 0.991	R_int = 0.027
3196 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.056	0 restraints
wR(F²) = 0.151	H-atom parameters constrained
S = 1.08	Δρ_max = 0.18 e Å⁻³
2895 reflections	Δρ_min = −0.17 e Å⁻³
194 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

	x	y	z	U_iso*/U_eq
C1	0.7983 (6)	1.3447 (4)	−0.0150 (2)	0.0938 (11)
H1A	0.6774	1.2848	−0.0132	0.141*
H1B	0.8108	1.3993	−0.0774	0.141*
H1C	0.7629	1.4130	0.0333	0.141*
C2	1.0269 (4)	1.1661 (3)	0.08912 (15)	0.0505 (6)
C3	0.8532 (4)	1.1641 (3)	0.16030 (17)	0.0565 (6)
H3A	0.7103	1.2225	0.1513	0.068*
C4	0.8905 (4)	1.0754 (3)	0.24524 (17)	0.0548 (6)
H4	0.7705	1.0752	0.2929	0.066*
C5	1.0983 (4)	0.9870 (2)	0.26254 (15)	0.0423 (5)
C6	1.2741 (4)	0.9919 (3)	0.19039 (16)	0.0553 (6)
H6	1.4182	0.9357	0.2001	0.066*
C7	1.2382 (4)	1.0786 (3)	0.10484 (17)	0.0621 (7)
H7	1.3573	1.0786	0.0568	0.074*
C8	1.1324 (4)	0.8926 (2)	0.35563 (15)	0.0462 (6)
C9	1.2916 (4)	0.9385 (3)	0.41980 (16)	0.0495 (6)
C10	1.0275 (4)	0.7750 (2)	0.38730 (16)	0.0500 (6)
H10	1.0582	0.7349	0.4498	0.060*
C11	0.8736 (4)	0.6996 (2)	0.34031 (15)	0.0466 (6)
C12	0.7562 (4)	0.5977 (3)	0.39652 (17)	0.0563 (7)
H12	0.7770	0.5821	0.4623	0.068*
C13	0.6106 (4)	0.5188 (3)	0.35884 (17)	0.0577 (7)
H13	0.5354	0.4505	0.3985	0.069*
C14	0.5767 (4)	0.5414 (2)	0.26176 (17)	0.0495 (6)
C15	0.6987 (4)	0.6386 (3)	0.20313 (16)	0.0550 (6)
H15	0.6826	0.6504	0.1370	0.066*
C16	0.8418 (4)	0.7169 (2)	0.24152 (16)	0.0521 (6)
H16	0.9198	0.7831	0.2013	0.063*
C17	0.2995 (5)	0.3745 (3)	0.2726 (2)	0.0746 (8)
H17A	0.3998	0.2948	0.3053	0.112*
H17B	0.2067	0.3345	0.2315	0.112*
H17C	0.2009	0.4283	0.3192	0.112*
O1	1.0108 (3)	1.2517 (2)	0.00292 (12)	0.0753 (6)
O2	1.3849 (3)	1.04878 (19)	0.39719 (11)	0.0674 (6)
O3	1.3251 (3)	0.85636 (19)	0.50110 (11)	0.0691 (6)
H3	1.4025	0.8958	0.5341	0.104*
O4	0.4348 (3)	0.47241 (18)	0.21611 (12)	0.0641 (5)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
C1	0.091 (2)	0.104 (2)	0.074 (2)	0.007 (2)	−0.0214 (18)	0.0273 (18)
C2	0.0525 (15)	0.0561 (14)	0.0426 (12)	−0.0126 (12)	−0.0038 (11)	0.0029 (10)
C3	0.0391 (13)	0.0660 (16)	0.0582 (14)	0.0010 (12)	−0.0025 (11)	0.0085 (12)
C4	0.0350 (12)	0.0696 (16)	0.0543 (14)	−0.0040 (11)	0.0048 (10)	0.0067 (12)
C5	0.0397 (12)	0.0455 (12)	0.0429 (12)	−0.0120 (10)	−0.0034 (9)	−0.0004 (9)
C6	0.0366 (13)	0.0690 (16)	0.0543 (14)	0.0024 (11)	0.0015 (11)	0.0018 (12)
C7	0.0468 (15)	0.0817 (18)	0.0506 (14)	−0.0023 (13)	0.0095 (12)	0.0054 (13)
C8	0.0419 (13)	0.0483 (13)	0.0475 (12)	−0.0076 (10)	−0.0032 (10)	0.0010 (10)
C9	0.0472 (13)	0.0552 (14)	0.0451 (13)	−0.0108 (11)	−0.0061 (11)	0.0061 (11)
C10	0.0515 (14)	0.0544 (14)	0.0432 (12)	−0.0101 (11)	−0.0037 (11)	0.0034 (10)
C11	0.0437 (13)	0.0481 (13)	0.0465 (13)	−0.0074 (10)	−0.0032 (10)	0.0030 (10)
C12	0.0595 (16)	0.0638 (16)	0.0461 (13)	−0.0183 (13)	−0.0028 (11)	0.0053 (11)
C13	0.0527 (15)	0.0620 (15)	0.0595 (15)	−0.0223 (12)	0.0017 (12)	0.0050 (12)
C14	0.0434 (13)	0.0456 (13)	0.0588 (14)	−0.0050 (11)	−0.0071 (11)	−0.0009 (11)
C15	0.0662 (16)	0.0519 (14)	0.0475 (13)	−0.0145 (12)	−0.0108 (12)	0.0059 (11)
C16	0.0544 (14)	0.0522 (14)	0.0502 (14)	−0.0178 (12)	−0.0027 (11)	0.0064 (11)
C17	0.0668 (18)	0.0648 (17)	0.097 (2)	−0.0284 (15)	−0.0050 (16)	−0.0028 (15)
O1	0.0737 (13)	0.0920 (14)	0.0513 (10)	−0.0045 (11)	−0.0040 (9)	0.0201 (9)
O2	0.0759 (12)	0.0728 (12)	0.0594 (11)	−0.0376 (10)	−0.0217 (9)	0.0176 (9)
O3	0.0865 (14)	0.0735 (12)	0.0535 (10)	−0.0355 (10)	−0.0255 (9)	0.0150 (9)
O4	0.0639 (11)	0.0610 (11)	0.0720 (11)	−0.0240 (9)	−0.0171 (9)	0.0030 (9)

Geometric parameters (Å, º) top

C1—O1	1.418 (3)	C9—O3	1.303 (2)
C1—H1A	0.9600	C10—C11	1.455 (3)
C1—H1B	0.9600	C10—H10	0.9300
C1—H1C	0.9600	C11—C12	1.384 (3)
C2—O1	1.364 (3)	C11—C16	1.398 (3)
C2—C3	1.368 (3)	C12—C13	1.371 (3)
C2—C7	1.385 (3)	C12—H12	0.9300
C3—C4	1.375 (3)	C13—C14	1.377 (3)
C3—H3A	0.9300	C13—H13	0.9300
C4—C5	1.376 (3)	C14—O4	1.356 (3)
C4—H4	0.9300	C14—C15	1.386 (3)
C5—C6	1.387 (3)	C15—C16	1.362 (3)
C5—C8	1.490 (3)	C15—H15	0.9300
C6—C7	1.372 (3)	C16—H16	0.9300
C6—H6	0.9300	C17—O4	1.423 (3)
C7—H7	0.9300	C17—H17A	0.9600
C8—C10	1.339 (3)	C17—H17B	0.9600
C8—C9	1.482 (3)	C17—H17C	0.9600
C9—O2	1.222 (3)	O3—H3	0.8200

O1—C1—H1A	109.5	C8—C10—C11	130.8 (2)
O1—C1—H1B	109.5	C8—C10—H10	114.6
H1A—C1—H1B	109.5	C11—C10—H10	114.6
O1—C1—H1C	109.5	C12—C11—C16	116.9 (2)
H1A—C1—H1C	109.5	C12—C11—C10	117.9 (2)
H1B—C1—H1C	109.5	C16—C11—C10	125.1 (2)
O1—C2—C3	124.8 (2)	C13—C12—C11	122.4 (2)
O1—C2—C7	116.4 (2)	C13—C12—H12	118.8
C3—C2—C7	118.8 (2)	C11—C12—H12	118.8
C2—C3—C4	119.8 (2)	C12—C13—C14	119.5 (2)
C2—C3—H3A	120.1	C12—C13—H13	120.3
C4—C3—H3A	120.1	C14—C13—H13	120.3
C3—C4—C5	122.6 (2)	O4—C14—C13	125.2 (2)
C3—C4—H4	118.7	O4—C14—C15	115.5 (2)
C5—C4—H4	118.7	C13—C14—C15	119.3 (2)
C4—C5—C6	117.04 (19)	C16—C15—C14	120.6 (2)
C4—C5—C8	121.03 (19)	C16—C15—H15	119.7
C6—C5—C8	121.9 (2)	C14—C15—H15	119.7
C7—C6—C5	121.0 (2)	C15—C16—C11	121.2 (2)
C7—C6—H6	119.5	C15—C16—H16	119.4
C5—C6—H6	119.5	C11—C16—H16	119.4
C6—C7—C2	120.8 (2)	O4—C17—H17A	109.5
C6—C7—H7	119.6	O4—C17—H17B	109.5
C2—C7—H7	119.6	H17A—C17—H17B	109.5
C10—C8—C9	117.8 (2)	O4—C17—H17C	109.5
C10—C8—C5	126.2 (2)	H17A—C17—H17C	109.5
C9—C8—C5	115.95 (18)	H17B—C17—H17C	109.5
O2—C9—O3	122.1 (2)	C2—O1—C1	118.0 (2)
O2—C9—C8	121.2 (2)	C9—O3—H3	109.5
O3—C9—C8	116.7 (2)	C14—O4—C17	118.3 (2)

O1—C2—C3—C4	−178.7 (2)	C9—C8—C10—C11	−176.6 (2)
C7—C2—C3—C4	−0.3 (4)	C5—C8—C10—C11	5.9 (4)
C2—C3—C4—C5	0.1 (4)	C8—C10—C11—C12	−168.2 (2)
C3—C4—C5—C6	0.9 (4)	C8—C10—C11—C16	14.8 (4)
C3—C4—C5—C8	179.8 (2)	C16—C11—C12—C13	−1.5 (4)
C4—C5—C6—C7	−1.7 (4)	C10—C11—C12—C13	−178.8 (2)
C8—C5—C6—C7	179.4 (2)	C11—C12—C13—C14	−0.5 (4)
C5—C6—C7—C2	1.5 (4)	C12—C13—C14—O4	−178.9 (2)
O1—C2—C7—C6	178.1 (2)	C12—C13—C14—C15	2.9 (4)
C3—C2—C7—C6	−0.4 (4)	O4—C14—C15—C16	178.3 (2)
C4—C5—C8—C10	66.9 (3)	C13—C14—C15—C16	−3.3 (4)
C6—C5—C8—C10	−114.2 (3)	C14—C15—C16—C11	1.3 (4)
C4—C5—C8—C9	−110.7 (2)	C12—C11—C16—C15	1.1 (3)
C6—C5—C8—C9	68.2 (3)	C10—C11—C16—C15	178.2 (2)
C10—C8—C9—O2	−176.7 (2)	C3—C2—O1—C1	−0.5 (4)
C5—C8—C9—O2	1.1 (3)	C7—C2—O1—C1	−178.9 (2)
C10—C8—C9—O3	2.9 (3)	C13—C14—O4—C17	3.6 (3)
C5—C8—C9—O3	−179.4 (2)	C15—C14—O4—C17	−178.2 (2)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O3—H3···O2ⁱ	0.82	1.80	2.608 (2)	169

Symmetry code: (i) −x+3, −y+2, −z+1.

Experimental details

Crystal data
Chemical formula	C₁₇H₁₆O₄
M_r	284.30
Crystal system, space group	Triclinic, P1
Temperature (K)	298
a, b, c (Å)	5.8690 (12), 9.1480 (18), 13.992 (3)
α, β, γ (°)	83.65 (3), 85.43 (3), 80.92 (3)
V (Å³)	735.8 (3)
Z	2
Radiation type	Mo Kα
µ (mm⁻¹)	0.09
Crystal size (mm)	0.30 × 0.20 × 0.10

Data collection
Diffractometer	Enraf–Nonius CAD-4 diffractometer
Absorption correction	ψ scan (North et al., 1968)
T_min, T_max	0.973, 0.991
No. of measured, independent and observed [I > 2σ(I)] reflections	3196, 2895, 1779
R_int	0.027
(sin θ/λ)_max (Å⁻¹)	0.616

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.056, 0.151, 1.08
No. of reflections	2895
No. of parameters	194
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.18, −0.17

Computer programs: CAD-4 Software (Enraf–Nonius, 1989), XCAD4 (Harms & Wocadlo, 1995), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O3—H3···O2ⁱ	0.82	1.80	2.608 (2)	168.7

Symmetry code: (i) −x+3, −y+2, −z+1.

Acknowledgements

This work was financed by a grant (Project 30772627) from the National Natural Science Foundation of China.

References

Enraf–Nonius (1989). CAD-4 Software. Enraf–Nonius, Delft, The Netherlands. Google Scholar
Harms, K. & Wocadlo, S. (1995). XCAD4. University of Marburg, Germany. Google Scholar
Huang, X.-F., Li, H.-Q., Shi, L., Li, H.-Q. & Zhu, H.-L. (2007). J. Chem. Crystallogr. 37, 739–742. Web of Science CSD CrossRef CAS Google Scholar
Huang, X.-F., Li, H.-Q., Shi, L., Xue, J.-Y., Ruan, B.-F. & Zhu, H.-L. (2008). Chem. Biodiver. 5, 636–642. Web of Science CSD CrossRef CAS Google Scholar
Huang, X.-F., Ruan, B.-F., Wang, X.-T., Xu, C., Ge, H.-M., Zhu, H.-L. & Tan, R.-X. (2007). Eur. J. Med. Chem. 42, 263–267. Web of Science CrossRef PubMed CAS Google Scholar
Jang, M., Cai, L., Udeani, G. O., Slowing, K. V., Thomas, C. F., Beecher, C. W. W., Fong, H. H. S., Farnsworth, N. R., Kinghorn, A. D., Mehta, R. G., Moon, R. C. & Pezztuo, J. M. (1997). Science, 275, 218–220. CrossRef CAS PubMed Web of Science Google Scholar
North, A. C. T., Phillips, D. C. & Mathews, F. S. (1968). Acta Cryst. A24, 351–359. CrossRef IUCr Journals Web of Science Google Scholar
Ruan, B.-F., Huang, X.-F., Ding, H., Xu, C., Ge, H.-M., Zhu, H.-L. & Tan, R.-X. (2006). Chem. Biodiver. 3, 975–981. Web of Science CrossRef CAS Google Scholar
Schulze, K., Schreiber, L. & Szankowski, I. (2005). J. Agric. Food Chem. 53, 356–362. Web of Science CrossRef PubMed CAS Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Shi, L., Huang, X.-F., Shi, L., Zhu, Z.-W., Li, H.-Q., Xue, J.-Y., Zhu, H.-L. & Liu, C.-H. (2008). Aust. J. Chem. 61, 472–475. Web of Science CrossRef CAS Google Scholar
Stomberg, R., Li, S.-M., Lundquist, K. & Norinder, U. (2001). J. Chem. Crystallogr. 31, 321–328. Web of Science CSD CrossRef CAS Google Scholar