Crystal structure of 3,5-di­methyl­phenyl 2-nitro­benzene­sulfonate

Atanasova, T.P.; Riley, S.; Biros, S.M.; Staples, R.J.; Ngassa, F.N.

doi:10.1107/S2056989015015078

research communications

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 71| Part 9| September 2015| Pages 1045-1047

https://doi.org/10.1107/S2056989015015078

Open

access

Crystal structure of 3,5-dimethylphenyl 2-nitrobenzenesulfonate

Tsvetelina P. Atanasova,^a Sean Riley,^a Shannon M. Biros,^a Richard J. Staples ^b and Felix N. Ngassa ^a ^*

^aDepartment of Chemistry, Grand Valley State University, 1 Campus Dr., Allendale, MI 49401, USA, and ^bCenter for Crystallographic Research, Department of Chemistry, Michigan State University, 578 S. Shaw Lane, East Lansing, MI 48824, USA
^*Correspondence e-mail: ngassaf@gvsu.edu

Edited by M. Gdaniec, Adam Mickiewicz University, Poland (Received 11 July 2015; accepted 12 August 2015; online 22 August 2015)

The title compound, C₁₄H₁₃NO₅S, was synthesized via a nucleophilic substitution reaction between 3,5-dimethylphenol and 2-nitrobenzenesulfonyl chloride. The aromatic rings attached to the SO₃ group are oriented in a gauche fashion around the ester S—O bond, with a C—S—O—C torsion angle of 84.68 (11)°. The molecules form centrosymmetric dimers via π–π stacking interactions between 3,5-dimethylphenyl groups (centroid–centroid distance = 3.709 Å). An intermolecular S=O⋯N interaction between the sulfonyl and nitro groups, with an O⋯N distance of 2.9840 (18) Å, organizes the dimers into columns extending along [011]. These columns are further assembled into (111) layers through C—H⋯O interactions.

Keywords: crystal structure; nitrobenzenesulfonate; N(nitro)⋯O interactions; C—H⋯O interactions; π–π interactions.

CCDC reference: 1418463

1. Chemical context

Microtubules form a major component of the cytoskeleton and have been implicated in a wide variety of cellular functions, such as cell division (Jordan & Wilson, 2004 ). Microtubules therefore have been targeted in the design of drugs for the treatment of various forms of cancer (Spencer & Faulds, 1994 ; Teicher, 2008 ; Trivedi et al., 2008 ). For example, Combretastatin A-4 (CA-4) has been shown to target tumor vasculature (Griggs et al., 2001 ). Most known antimicrotubules have poor biopharmaceutical properties, uch as chemoresistance and toxicity (Islam et al., 2003 ; Fortin et al., 2011 ).

Research in the field for the synthesis of new antimicrotubule compounds has been geared towards compounds with improved biopharmaceutical properties (Fortin et al., 2011). To this end, Fortin and co-workers have designed and synthesized various sulfonate derivatives, which have been tested as new tubulin inhibitors mimicking Combretastatin A-4 (Fig. 1).

Figure 1
The structures of CA-4 and sulfonate analogues, where R₁ and R₂ are substituents on the sulfonyl and phenoxy benzene rings, respectively.

A series of sulfonate derivatives have shown promise as anticancer drugs, with some having lower toxicity than CA-4 (Fortin et al., 2011). We embarked on the synthesis of sulfonate derivatives with the long-term goal of investigating the effect of the benzene-ring substituents on the cytotoxicity of the sulfonate derivatives. To the best of our knowledge, despite the simplicity of the sulfonate derivatives, there has been no relevant previous crystallographic studies. Therefore, we report here the synthesis and crystal structure of 3,5-dimethylphenyl 2-nitrobenzenesulfonate.

2. Structural commentary

In the title molecule (Fig. 2), the O1=S1=O2 and C1—S1—O3 bond angles of 119.41 (7) and 104.16 (6)° are typical for phenyl benzenesulfonates with a gauche conformation around the ester S—O bond. The torsion angle C1—S1—O3—C7 around the ester bond is −84.68 (11)°. Owing to steric hindrance between the ortho substituents of the benzene ring, the nitro group is twisted relative to the benzene best plane by 39.91 (2)°, so that the shortest contact of 2.7941 (16) Å between the O atoms of these groups is close to the sum of the van der Waals radii.

Figure 2
The molecular structure of the title compound, with displacement ellipsoids shown at the 50% probability level. All H atoms have been omitted for clarity. Color codes: black C, blue N, red O and yellow S.

3. Supramolecular features

The molecules of the title compound form centrosymmetric dimers via intermolecular π–π stacking interactions between the relatively electron-rich C7–C12 benzene rings (Fig. 3), with a plane-to-plane distance of 3.4147 (15) Å. The aromatic rings are stacked with an offset, and the distance between the centroids of these rings is 3.709 (12) Å. Another centrosymmetric dimer is formed by an S=O⋯N interaction, with an N1⋯O2 interatomic distance of 2.9840 (18) Å. O⋯N(nitro) interactions between nitro groups have been discussed in the literature (Daszkiewicz, 2013 ; Caracelli et al., 2014 ) and we report here the case of sulfonyl and nitro group interactions. Both types of dimers are assembled into a column-type structure extending along [011] (Fig. 4).

Figure 3
The centrosymmetric dimers formed by intermolecular offset π–π stacking interactions. [Symmetry code: (i) −x + 1, −y + 2, −z.]

Figure 4
The packing of molecules in the crystal, viewed down the [110] direction. Columns of dimers formed via stacking interactions are colored green and pink in an alternating fashion, and potential N⋯O=S interactions are denoted with blue dashed lines.

There are no classical hydrogen bonds in the crystal structure; however, nonclassical C—H⋯O interactions between aromatic-ring H atoms and sulfonyl and nitro group O atoms organize the [011] columns into (111) layers. The geometry of these interactions is given in Table 1.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C5—H5⋯O1ⁱ	0.95	2.56	3.4544 (19)	156
C8—H8⋯O5ⁱⁱ	0.95	2.56	3.468 (2)	160
Symmetry codes: (i) x+1, y-1, z; (ii) x-1, y+1, z.

4. Database survey

The Cambridge Structural Database (CSD, Version 5.36 with two updates; Groom & Allen, 2014 ) contains three structures with an o-nitroarylsulfonyl moiety bonded to an aromatic ring through an ester linkage. These are CSD refcodes FEMQUK (Ichikawa et al., 2004 ), MIBZUT (Pelly et al., 2007 ), and FEMRIZ (Ichikawa et al., 2004). Like in the title compound, the aromatic substituents of the SO₃ group are oriented gauche around the ester S—O bond and the absolute value of the C—S—O—C torsion angle is in the range 85.9 (3)–103.43 (13)°. In each of these structures there are either intra- or intermolecular S=O⋯N interactions between the sulfonate and o-nitro groups.

5. Synthesis and crystallization

3,5-Dimethylphenol (2.44 g, 20 mmol) was dissolved in chilled dichloromethane (25 ml). This was followed by the addition of pyridine (3.2 ml, 40 mmol). The resulting solution was cooled in an ice bath under an N₂ atmosphere, followed by the addition of 2-nitrobenzenesulfonyl chloride (4.43 g, 20 mmol) portion-wise. The mixture was stirred at 273 K for 30 mins and then at room temperature for 24 h. The product precipitated from the reaction mixture after sitting at 277 K for two weeks. The product was redissolved in dichloromethane, and the solvent was allowed to evaporate slowly to give large block-shaped crystals that were suitable for analysis by X-ray diffraction (m.p. 374–378 K).

6. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. H atoms were placed in calculated positions and constrained to ride on their parent atoms, with U_iso(H) = 1.2U_eq(C) for CH groups and 1.5U_eq(C) for methyl groups.

Table 2
Experimental details

Crystal data
Chemical formula	C₁₄H₁₃NO₅S
M_r	307.31
Crystal system, space group	Triclinic, P $[\overline{1}]$
Temperature (K)	173
a, b, c (Å)	7.9958 (4), 7.9991 (5), 12.0238 (3)
α, β, γ (°)	83.908 (3), 76.286 (3), 63.411 (4)
V (Å³)	668.10 (6)
Z	2
Radiation type	Cu Kα
μ (mm⁻¹)	2.37
Crystal size (mm)	0.38 × 0.34 × 0.21

Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	Multi-scan (SADABS; Bruker, 2013 )
T_min, T_max	0.630, 0.754
No. of measured, independent and observed [I > 2σ(I)] reflections	10317, 2519, 2461
R_int	0.022
(sin θ/λ)_max (Å⁻¹)	0.617

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.035, 0.092, 1.05
No. of reflections	2519
No. of parameters	192
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.33, −0.50
Computer programs: APEX2 and SAINT (Bruker, 2013), SHELXS97 (Sheldrick, 2008 ), SHELXL2014 (Sheldrick, 2015 ), CrystalMaker (Palmer, 2007 ) and OLEX2 (Dolomanov et al., 2009 ; Bourhis et al., 2015 ).

Supporting information

CCDC reference: 1418463

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2056989015015078/gk2639sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989015015078/gk2639Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S2056989015015078/gk2639Isup3.cml

checkCIF report

Computing details top

Data collection: APEX2 (Bruker, 2013); cell refinement: SAINT (Bruker, 2013); data reduction: SAINT (Bruker, 2013); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: CrystalMaker (Palmer, 2007); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009; Bourhis et al., 2015).

3,5-Dimethylphenyl 2-nitrobenzenesulfonate top

Crystal data top

C₁₄H₁₃NO₅S	Z = 2
M_r = 307.31	F(000) = 320
Triclinic, P1	D_x = 1.528 Mg m⁻³
a = 7.9958 (4) Å	Cu Kα radiation, λ = 1.54178 Å
b = 7.9991 (5) Å	Cell parameters from 8863 reflections
c = 12.0238 (3) Å	θ = 3.8–72.3°
α = 83.908 (3)°	µ = 2.37 mm⁻¹
β = 76.286 (3)°	T = 173 K
γ = 63.411 (4)°	Block, colourless
V = 668.10 (6) Å³	0.38 × 0.34 × 0.21 mm

Data collection top

Bruker APEXII CCD diffractometer	2519 independent reflections
Radiation source: sealed tube	2461 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.022
Detector resolution: 8 pixels mm^-1	θ_max = 72.1°, θ_min = 3.8°
φ and ω scans	h = −9→9
Absorption correction: multi-scan (SADABS; Bruker, 2013)	k = −9→9
T_min = 0.630, T_max = 0.754	l = −14→14
10317 measured reflections

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.035	H-atom parameters constrained
wR(F²) = 0.092	w = 1/[σ²(F_o²) + (0.0559P)² + 0.3536P] where P = (F_o² + 2F_c²)/3
S = 1.05	(Δ/σ)_max < 0.001
2519 reflections	Δρ_max = 0.33 e Å⁻³
192 parameters	Δρ_min = −0.50 e Å⁻³
0 restraints

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
S1	0.32156 (5)	0.85859 (5)	0.36621 (3)	0.01694 (13)
O1	0.27175 (16)	1.05073 (15)	0.33973 (10)	0.0239 (3)
O2	0.22079 (15)	0.81004 (16)	0.46826 (9)	0.0240 (3)
O3	0.29830 (15)	0.76150 (15)	0.26599 (9)	0.0193 (2)
O4	0.46725 (16)	0.43665 (16)	0.39045 (10)	0.0240 (3)
O5	0.73130 (19)	0.28883 (18)	0.26840 (12)	0.0375 (3)
N1	0.62367 (18)	0.41785 (18)	0.33520 (11)	0.0201 (3)
C1	0.5719 (2)	0.7475 (2)	0.36177 (12)	0.0171 (3)
C2	0.6508 (2)	0.8662 (2)	0.37453 (13)	0.0216 (3)
H2	0.5728	0.9973	0.3801	0.026*
C3	0.8425 (2)	0.7951 (3)	0.37920 (14)	0.0258 (4)
H3	0.8939	0.8771	0.3902	0.031*
C4	0.9587 (2)	0.6047 (3)	0.36792 (14)	0.0265 (4)
H4	1.0898	0.5564	0.3711	0.032*
C5	0.8841 (2)	0.4845 (2)	0.35195 (13)	0.0227 (3)
H5	0.9643	0.3542	0.3426	0.027*
C6	0.6920 (2)	0.5556 (2)	0.34977 (12)	0.0182 (3)
C7	0.3244 (2)	0.8273 (2)	0.15112 (12)	0.0175 (3)
C8	0.1844 (2)	0.9933 (2)	0.12119 (13)	0.0200 (3)
H8	0.0770	1.0683	0.1773	0.024*
C9	0.2044 (2)	1.0482 (2)	0.00677 (14)	0.0214 (3)
C10	0.3619 (2)	0.9314 (2)	−0.07306 (13)	0.0217 (3)
H10	0.3744	0.9677	−0.1513	0.026*
C11	0.5014 (2)	0.7635 (2)	−0.04207 (13)	0.0198 (3)
C12	0.4822 (2)	0.7111 (2)	0.07297 (13)	0.0186 (3)
H12	0.5755	0.5979	0.0971	0.022*
C13	0.0582 (3)	1.2305 (2)	−0.02968 (16)	0.0294 (4)
H13A	−0.0609	1.2720	0.0288	0.044*
H13B	0.0333	1.2131	−0.1026	0.044*
H13C	0.1069	1.3249	−0.0390	0.044*
C14	0.6690 (2)	0.6430 (2)	−0.13189 (14)	0.0249 (3)
H14A	0.6251	0.6435	−0.2015	0.037*
H14B	0.7263	0.5147	−0.1032	0.037*
H14C	0.7647	0.6923	−0.1494	0.037*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
S1	0.01488 (19)	0.0172 (2)	0.0159 (2)	−0.00464 (15)	−0.00261 (13)	−0.00112 (14)
O1	0.0254 (6)	0.0177 (6)	0.0258 (6)	−0.0055 (4)	−0.0081 (5)	−0.0009 (5)
O2	0.0186 (5)	0.0292 (6)	0.0188 (5)	−0.0075 (5)	−0.0002 (4)	0.0000 (5)
O3	0.0225 (5)	0.0206 (5)	0.0174 (5)	−0.0113 (4)	−0.0061 (4)	0.0026 (4)
O4	0.0227 (6)	0.0257 (6)	0.0254 (6)	−0.0129 (5)	−0.0043 (5)	0.0023 (5)
O5	0.0340 (7)	0.0311 (7)	0.0430 (8)	−0.0111 (6)	0.0021 (6)	−0.0198 (6)
N1	0.0215 (6)	0.0181 (6)	0.0186 (6)	−0.0063 (5)	−0.0052 (5)	0.0000 (5)
C1	0.0157 (7)	0.0211 (7)	0.0126 (6)	−0.0072 (6)	−0.0014 (5)	−0.0007 (6)
C2	0.0236 (7)	0.0231 (8)	0.0179 (7)	−0.0108 (6)	−0.0017 (6)	−0.0027 (6)
C3	0.0258 (8)	0.0362 (9)	0.0219 (8)	−0.0194 (7)	−0.0024 (6)	−0.0044 (7)
C4	0.0170 (7)	0.0397 (10)	0.0227 (8)	−0.0124 (7)	−0.0034 (6)	−0.0006 (7)
C5	0.0183 (7)	0.0240 (8)	0.0195 (7)	−0.0046 (6)	−0.0021 (6)	−0.0001 (6)
C6	0.0187 (7)	0.0212 (7)	0.0137 (7)	−0.0087 (6)	−0.0017 (5)	−0.0006 (6)
C7	0.0210 (7)	0.0189 (7)	0.0169 (7)	−0.0116 (6)	−0.0064 (6)	0.0016 (6)
C8	0.0191 (7)	0.0189 (7)	0.0226 (8)	−0.0074 (6)	−0.0060 (6)	−0.0029 (6)
C9	0.0244 (7)	0.0177 (7)	0.0256 (8)	−0.0098 (6)	−0.0114 (6)	0.0021 (6)
C10	0.0304 (8)	0.0213 (8)	0.0181 (7)	−0.0145 (7)	−0.0086 (6)	0.0030 (6)
C11	0.0238 (7)	0.0188 (7)	0.0208 (7)	−0.0127 (6)	−0.0038 (6)	−0.0023 (6)
C12	0.0196 (7)	0.0146 (7)	0.0233 (8)	−0.0077 (6)	−0.0073 (6)	0.0010 (6)
C13	0.0324 (9)	0.0217 (8)	0.0327 (9)	−0.0074 (7)	−0.0158 (7)	0.0046 (7)
C14	0.0288 (8)	0.0225 (8)	0.0230 (8)	−0.0121 (7)	−0.0017 (6)	−0.0035 (6)

Geometric parameters (Å, º) top

S1—O1	1.4249 (12)	C7—C8	1.380 (2)
S1—O2	1.4198 (11)	C7—C12	1.383 (2)
S1—O3	1.5887 (11)	C8—H8	0.9500
S1—C1	1.7797 (15)	C8—C9	1.393 (2)
O3—C7	1.4268 (18)	C9—C10	1.394 (2)
O4—N1	1.2195 (17)	C9—C13	1.505 (2)
O5—N1	1.2263 (18)	C10—H10	0.9500
N1—C6	1.473 (2)	C10—C11	1.392 (2)
C1—C2	1.391 (2)	C11—C12	1.395 (2)
C1—C6	1.400 (2)	C11—C14	1.507 (2)
C2—H2	0.9500	C12—H12	0.9500
C2—C3	1.389 (2)	C13—H13A	0.9800
C3—H3	0.9500	C13—H13B	0.9800
C3—C4	1.385 (3)	C13—H13C	0.9800
C4—H4	0.9500	C14—H14A	0.9800
C4—C5	1.387 (2)	C14—H14B	0.9800
C5—H5	0.9500	C14—H14C	0.9800
C5—C6	1.385 (2)

O1—S1—O3	109.83 (6)	C8—C7—C12	123.31 (14)
O1—S1—C1	106.85 (7)	C12—C7—O3	117.36 (13)
O2—S1—O1	119.41 (7)	C7—C8—H8	120.8
O2—S1—O3	105.16 (6)	C7—C8—C9	118.42 (14)
O2—S1—C1	110.43 (7)	C9—C8—H8	120.8
O3—S1—C1	104.16 (6)	C8—C9—C10	118.82 (14)
C7—O3—S1	120.43 (9)	C8—C9—C13	120.43 (15)
O4—N1—O5	124.23 (14)	C10—C9—C13	120.75 (15)
O4—N1—C6	118.87 (12)	C9—C10—H10	118.9
O5—N1—C6	116.89 (13)	C11—C10—C9	122.27 (15)
C2—C1—S1	115.24 (12)	C11—C10—H10	118.9
C2—C1—C6	118.36 (14)	C10—C11—C12	118.57 (14)
C6—C1—S1	126.38 (12)	C10—C11—C14	120.02 (14)
C1—C2—H2	119.7	C12—C11—C14	121.41 (14)
C3—C2—C1	120.67 (15)	C7—C12—C11	118.60 (14)
C3—C2—H2	119.7	C7—C12—H12	120.7
C2—C3—H3	119.9	C11—C12—H12	120.7
C4—C3—C2	120.11 (15)	C9—C13—H13A	109.5
C4—C3—H3	119.9	C9—C13—H13B	109.5
C3—C4—H4	119.9	C9—C13—H13C	109.5
C3—C4—C5	120.10 (15)	H13A—C13—H13B	109.5
C5—C4—H4	119.9	H13A—C13—H13C	109.5
C4—C5—H5	120.2	H13B—C13—H13C	109.5
C6—C5—C4	119.59 (15)	C11—C14—H14A	109.5
C6—C5—H5	120.2	C11—C14—H14B	109.5
C1—C6—N1	122.82 (13)	C11—C14—H14C	109.5
C5—C6—N1	116.05 (14)	H14A—C14—H14B	109.5
C5—C6—C1	121.13 (14)	H14A—C14—H14C	109.5
C8—C7—O3	119.06 (13)	H14B—C14—H14C	109.5

S1—O3—C7—C8	−74.03 (15)	C1—S1—O3—C7	−84.68 (11)
S1—O3—C7—C12	111.80 (13)	C1—C2—C3—C4	1.8 (2)
S1—C1—C2—C3	176.26 (12)	C2—C1—C6—N1	−179.70 (14)
S1—C1—C6—N1	2.0 (2)	C2—C1—C6—C5	0.8 (2)
S1—C1—C6—C5	−177.44 (12)	C2—C3—C4—C5	0.0 (2)
O1—S1—O3—C7	29.44 (12)	C3—C4—C5—C6	−1.3 (2)
O1—S1—C1—C2	21.24 (13)	C4—C5—C6—N1	−178.57 (13)
O1—S1—C1—C6	−160.46 (13)	C4—C5—C6—C1	0.9 (2)
O2—S1—O3—C7	159.13 (10)	C6—C1—C2—C3	−2.2 (2)
O2—S1—C1—C2	−110.09 (12)	C7—C8—C9—C10	1.6 (2)
O2—S1—C1—C6	68.21 (15)	C7—C8—C9—C13	−178.43 (14)
O3—S1—C1—C2	137.46 (11)	C8—C7—C12—C11	0.0 (2)
O3—S1—C1—C6	−44.23 (14)	C8—C9—C10—C11	−1.1 (2)
O3—C7—C8—C9	−174.87 (12)	C9—C10—C11—C12	0.0 (2)
O3—C7—C12—C11	173.85 (12)	C9—C10—C11—C14	−179.82 (14)
O4—N1—C6—C1	−39.7 (2)	C10—C11—C12—C7	0.6 (2)
O4—N1—C6—C5	139.82 (14)	C12—C7—C8—C9	−1.1 (2)
O5—N1—C6—C1	141.33 (16)	C13—C9—C10—C11	178.94 (14)
O5—N1—C6—C5	−39.2 (2)	C14—C11—C12—C7	−179.61 (13)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C5—H5···O1ⁱ	0.95	2.56	3.4544 (19)	156
C8—H8···O5ⁱⁱ	0.95	2.56	3.468 (2)	160

Symmetry codes: (i) x+1, y−1, z; (ii) x−1, y+1, z.

Acknowledgements

The authors thank GVSU for financial support (Weldon Fund, CSCE), the NSF for a 300 MHz Jeol FT–NMR (CCLI-0087655), and Pfizer, Inc. for the donation of a Varian Inova 400 FT–NMR. The CCD-based X-ray diffractometers at Michigan State University were upgraded and/or replaced by departmental funds.

References

Bourhis, L. J., Dolomanov, O. V., Gildea, R. J., Howard, J. A. K. & Puschmann, H. (2015). Acta Cryst. A71, 59–75. Web of Science CrossRef IUCr Journals Google Scholar
Bruker (2013). APEX2, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Caracelli, I., Maganhi, S. H., Moran, P. J. S., Paula, B. R. S. de, Delling, F. N. & Tiekink, E. R. T. (2014). Acta Cryst. E70, o1051–o1052. CSD CrossRef IUCr Journals Google Scholar
Daszkiewicz, M. (2013). CrystEngComm, 15, 10427–10430. Web of Science CrossRef CAS Google Scholar
Dolomanov, O. V., Bourhis, L. J., Gildea, R. J., Howard, J. A. K. & Puschmann, H. (2009). J. Appl. Cryst. 42, 339–341. Web of Science CrossRef CAS IUCr Journals Google Scholar
Fortin, S., Wei, L., Moreau, E., Lacroix, J., Côté, M.-F., Petitclerc, É., Kotra, L. P. & Gaudreault, R. C. (2011). J. Med. Chem. 54, 4559–4580. CrossRef CAS PubMed Google Scholar
Griggs, J., Metcalfe, J. C. & Hesketh, R. (2001). Lancet Oncol. 2, 82–87. CrossRef PubMed CAS Google Scholar
Groom, C. R. & Allen, F. H. (2014). Angew. Chem. Int. Ed. 53, 662–671. Web of Science CSD CrossRef CAS Google Scholar
Ichikawa, M., Takahashi, M., Aoyagi, S. & Kibayashi, C. (2004). J. Am. Chem. Soc. 126, 16553–16558. CSD CrossRef PubMed CAS Google Scholar
Islam, M. N., Song, Y. & Iskander, M. N. (2003). J. Mol. Graph. Model. 21, 263–272. CrossRef PubMed CAS Google Scholar
Jordan, M. A. & Wilson, L. (2004). Nat. Rev. Cancer, 4, 253–265. CrossRef PubMed CAS Google Scholar
Palmer, D. (2007). CrystalMaker. CrystalMaker Software, Bicester, England. Google Scholar
Pelly, S. C., Govener, S., Fernades, M. A., Schmalz, H.-G. & de Koning, C. B. (2007). J. Org. Chem. 72, 2857–2864. CSD CrossRef PubMed CAS Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Sheldrick, G. M. (2015). Acta Cryst. C71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Spencer, C. M. & Faulds, D. (1994). Drugs, 48, 794–847. CrossRef CAS PubMed Google Scholar
Teicher, B. A. (2008). Clin. Cancer Res. 14, 1610–1617. CrossRef PubMed CAS Google Scholar
Trivedi, M., Budihardjo, I., Loureiro, K., Reid, T. R. & Ma, J. D. (2008). Future Oncol. 4, 483–500. CrossRef PubMed CAS Google Scholar