Crystal structure and Hirshfeld surface analysis of ethyl 5-phenyl­isoxazole-3-carboxyl­ate

Shaik, A.; Kirubakaran, S.; Thiruvenkatam, V.

doi:10.1107/S2056989017003127

research communications

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 73| Part 4| April 2017| Pages 531-534

https://doi.org/10.1107/S2056989017003127

Open

access

Crystal structure and Hirshfeld surface analysis of ethyl 5-phenylisoxazole-3-carboxylate

Althaf Shaik,^a Sivapriya Kirubakaran ^a and Vijay Thiruvenkatam ^b ^*

^aDepartment of Chemistry, IIT Gandhinagar, Gujarat, and ^bDepartment of Physics & Bio-Engineering, IIT Gandhinagar, Palaj Campus, Gandhinagar, Gujarat
^*Correspondence e-mail: vijay@iitgn.ac.in

Edited by H. Stoeckli-Evans, University of Neuchâtel, Switzerland (Received 1 February 2017; accepted 24 February 2017; online 17 March 2017)

The title compound, C₁₂H₁₁NO₃, is an intermediate used in the synthesis of many drug-like molecules. The molecule is almost planar, with the phenyl ring inclined to the isoxazole ring by 0.5 (1)°. The ester moiety has an extended conformation and is almost in the same plane with respect to the isoxazole ring, as indicated by the O—C—C—N torsion angle of −172.86 (18)°. In the crystal, molecules are linked via pairs of C—H⋯O hydrogen bonds with the same acceptor atom, forming inversion dimers with two R₂¹(7) ring motifs. The molecules stack in layers lying parallel to (10-3). Analysis using Hirshfeld surface generation and two-dimensional fingerprint plots explores the distribution of weak intermolecular interactions in the crystal structure.

Keywords: crystal structure; isoxazole derivative; drug intermediate; Hirshfeld surface; hydrogen bonding.

CCDC reference: 1534636

1. Chemical context

Nitrogen-containing heterocyclic rings are of great importance in medicinal and organic chemistry (Dou et al., 2013 ). Isoxazole derivatives are important heterocyclic pharmaceuticals having a broad spectrum of biological activity, which includes antagonism of the NMDA receptor, anti-inflammatory (Panda et al., 2009 ), anti-tumour, anticonvulsant, anti-psychotic, anti-depressant and anti HIV activity (Conti et al., 2005 ; Srivastava et al., 1999 ). Considerable attention has been paid to isoxazole derivatives as a result of their prominent biological properties (Dou et al., 2013). Valdecoxib (Bextra), a selective cyclooxygenase-2 (COX-2) inhibitor used in the treatment of arthritis, contains an isoxazole moiety which is responsible for its biological activity (Waldo & Larock, 2007 ; Dadiboyena & Nefzi, 2010 ). In addition, isoxazole derivatives are also important intermediates in the preparation of various heterocyclic biologically active drugs (Dou et al., 2013). As part of our ongoing studies on isoxazole derivatives as kinase inhibitors, we have synthesized the title compound, and report herein on its crystal structure and the quantitative analysis of intermolecular interactions using the Hirshfeld surface and 2D fingerprint plot analysis.

2. Structural commentary

The molecular structure of the title compound, (I), is illustrated in Fig. 1. The molecule consists of three almost flat units: the phenyl ring, the isoxazole ring and the ester. The phenyl (C1–C6) and isoxazole (O1/N1/C7–C9) rings are almost coplanar, as indicated by the torsion angle C5—C6—C7—O1 = 0.1 (3)°. The ester unit has an extended conformation and is almost in the same plane as the isoxazole ring, as indicated by the torsion angle O2—C10—C9—N1 = −172.86 (18)°.

Figure 1
The molecular structure of compound (I)

, with the atom labelling and displacement ellipsoid drawn at the 50% probability level.

3. Supramolecular features

In the crystal of (I), molecules are linked via pairs of C—H⋯O hydrogen bonds, both involving atom O2 as acceptor, forming inversion dimers with two R₂¹(7) ring motifs (Table 1 and Fig. 2). The molecules stack in layers lying parallel to (10 $[\overline{3}]$ ), as illustrated in Fig. 3.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C1—H1⋯O2ⁱ	0.93	2.52	3.447 (2)	171
C8—H8⋯O2ⁱ	0.93	2.36	3.260 (2)	163
Symmetry code: (i) -x-1, -y+1, -z.

Figure 2
Crystal packing of compound (I)

, viewed along the a axis. Hydrogen bonds are shown as dashed lines (see Table 1

Figure 3
Crystal packing of compound (I)

viewed along the b axis. Hydrogen bonds are shown as dashed lines and, for clarity, H atoms have been omitted.

4. Hirshfeld surface and fingerprint plot analysis

To explore the weak intermolecular interactions in (I), Hirshfeld surfaces and 2D fingerprint plots were generated using Crystal Explorer 3.1 to quantify the intermolecular interactions (McKinnon et al., 2007 ; Spackman & Jayatilaka, 2009 ). Hirshfeld surfaces are produced through the partitioning of space within a crystal where the ratio of promolecule to procrystal electron density is equal to 0.5, generating continuous, non-overlapping surfaces which are widely used to visualize and study the significance of weak interactions in the molecular packing (McKinnon et al., 2007). The Hirshfeld surface of title compound was mapped over d_norm, shape index and curvedness. The d_norm surface is the normalized function of d_i and d_e (Fig. 4a), with white-, red- and blue-coloured surfaces. The white surface indicates those contacts with distances equal to the sum of the van der Waals (vdW) radii, red indicates shorter contacts (< vdW radii) and blue the longer contact (> vdW radii). The Hirshfeld surface was also mapped over electrostatic potential (Fig. 4b) using a STO-3G basis set at the Hartee–Fock level of theory (Spackman & McKinnon, 2002 ; McKinnon et al., 2004 ). In the Hirshfeld surface, a pair of interactions between the aromatic C—H⋯O=C atoms can be seen as the bright-red area (1) in Fig. 5a. The 2D fingerprint plot analysis of the O⋯H interactions revealed significant hydrogen-bonding spikes (d_i = 1.3, d_e = 0.9 Å and d_e = 1.9, d_i = 2.6 Å); Fig. 6c.

Figure 4
Hirshfeld surface mapped over (a) d_norm and (b) electrostatic potential.

Figure 5
Hirshfeld surface mapped over (a) d_norm highlighting the regions of C—H⋯O hydrogen bonding and (b) d_norm highlighting the region of C—H⋯N hydrogen bonding.

Figure 6
Two-dimensional fingerprint plot analysis (a) all interactions, (b) H⋯H contacts, (c) O⋯H contacts, (d) N⋯H contacts, (e) C⋯H contacts and (f) C⋯C contacts.

The analysis indicates that there is a weak N⋯H intermolecular interaction between the nitrogen atom of the isoxazole ring and the methylene hydrogen atom of the phenyl ring of a neighbouring molecule (Fig. 5b). The fingerprint plot analysis of N⋯H contacts reveals a significant wing-like structure (d_i = 1.2, d_e = 1.5 Å and d_e = 2.2, d_i = 2.4 Å) Fig. 6d.

The relative contributions to the Hirshfeld surface area for each type of intermolecular contact are illustrated in Figs. 6 and 7. The H⋯H interactions appear as scattered points over nearly the entire plot and have a significant composition of 41% of the Hirshfeld surface. The H⋯O contacts comprise of 18.7% and the C⋯C interactions comprise 1.6% of the total Hirshfeld surface. The C⋯H and N⋯H interactions cover 23.2% and 9.2% of the surface, respectively. Thus, these weak interactions contribute significantly to the packing of (I).

Figure 7
Relative contribution of each interaction in the two-dimensional fingerprint analysis.

5. Database survey

A search of the Cambridge Structural Database (CSD, V5.38; last update November 2016; Groom et al., 2016 ) for similar isoxazole derivatives, revealed only one hit, viz. ethyl 5-(4-aminophenyl) isoxazole-3-carboxylate (CSD refcode YAVRIY; Zhao et al., 2012 ). This compound crystallizes with two independent molecules in the asymmetric unit. One molecule is slightly more planar than the other, with the phenyl ring being inclined to the isoxazole ring by 1.77 (10) and 5.85 (10)°. In the title compound, (I), this dihedral angle is 0.5 (1)°.

6. Synthesis and crystallization

There are several methods available in the literature for the preparation of isoxazole derivatives. We have followed a simple preparation from a diketoester (Tourteau et al., 2013 ; Bastos et al., 2015 ). After the reaction of acetophenone with diethyoxalate in a basic solution (sodium ethoxide) of ethanol for 8 h, 1N HCl was added to neutralize the sodium ethoxide to obtain the diketoester (ethyl 2,4-dioxo-4-phenylbutanoate; see Fig. 8) as a yellow liquid. 1 g (4.5 mmol) of the diketoester in ethanol was added to hydroxyl amine hydrochloride (0.315 g, 4.5 mmol) at room temperature and the resulting mixture was stirred at 353 K for 12 h. The progress of the reaction was monitored by TLC. After the completion of starting materials, the reaction mixture was cooled to room temperature and the excess of ethanol removed. The resulting residue was dissolved in water and extracted with ethyl acetate. The organic layer was dried with Na₂SO₄, filtered and the concentrated under reduced pressure. The resulting residue was purified by silica gel column chromatography (3% ethyl acetate: Pet-ether) to afford the title compound, (I) (yield 76.9%, 0.75 g; m.p. 325–327 K).

Figure 8
Synthesis of the title compound, (I)

Colourless crystals were obtained by slow evaporation of a solution in ethyl acetate. Spectroscopic data: ¹H NMR (500 MHz, chloroform-d) δ 7.80 (m, 2H), 7.50 (m, 3H), 6.92 (s, 1H), 4.47 (q, 2H), 1.44 (t, 3H). ¹³C NMR (126 MHz, chloroform-d) δ 171.66, 159.98, 156.96, 130.76, 129.11, 126.61, 125.89, 99.92, 62.18, 14.15.

7. Refinement

Crystal data, data collection and structure refinement parameters are given in Table 2. All H atoms were positioned geometrically and refined as riding: C—H = 0.95–0.99 Å with U_iso(H) = 1.2U_eq(C).

Table 2
Experimental details

Crystal data
Chemical formula	C₁₂H₁₁NO₃
M_r	217.22
Crystal system, space group	Monoclinic, P2₁/n
Temperature (K)	100
a, b, c (Å)	5.4447 (7), 17.180 (2), 11.7603 (19)
β (°)	94.508 (5)
V (Å³)	1096.6 (3)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	0.10
Crystal size (mm)	0.4 × 0.2 × 0.2

Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	–
No. of measured, independent and observed [I > 2σ(I)] reflections	14119, 2813, 1889
R_int	0.075
(sin θ/λ)_max (Å⁻¹)	0.676

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.064, 0.177, 1.09
No. of reflections	2813
No. of parameters	146
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.27, −0.30
Computer programs: APEX2 and SAINT (Bruker, 2006 ), SHELXS97 and SHELXTL (Sheldrick 2008 ), SHELXL2014 (Sheldrick, 2015 ), and Mercury (Macrae et al., 2008 ).

Supporting information

CCDC reference: 1534636

Crystal structure: contains datablocks I, Global. DOI: https://doi.org/10.1107/S2056989017003127/su5350sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989017003127/su5350Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S2056989017003127/su5350Isup5.cml

Supporting information file. DOI: https://doi.org/10.1107/S2056989017003127/su5350sup3.png

Supporting information file. DOI: https://doi.org/10.1107/S2056989017003127/su5350sup4.png

checkCIF report

Computing details top

Data collection: APEX2 (Bruker, 2006); cell refinement: SAINT (Bruker, 2006); data reduction: SAINT (Bruker, 2006); program(s) used to solve structure: SHELXS97 (Sheldrick 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: SHELXTL (Sheldrick 2008) and Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXTL (Sheldrick 2008).

Ethyl 5-phenylisoxazole-3-carboxylate top

Crystal data top

C₁₂H₁₁NO₃	F(000) = 456
M_r = 217.22	D_x = 1.316 Mg m⁻³
Monoclinic, P2₁/n	Mo Kα radiation, λ = 0.71073 Å
a = 5.4447 (7) Å	Cell parameters from 5392 reflections
b = 17.180 (2) Å	θ = 2.4–30.5°
c = 11.7603 (19) Å	µ = 0.10 mm⁻¹
β = 94.508 (5)°	T = 100 K
V = 1096.6 (3) Å³	Blocks, colourless
Z = 4	0.4 × 0.2 × 0.2 mm

Data collection top

Bruker APEXII CCD diffractometer	R_int = 0.075
φ and ω scans	θ_max = 28.7°, θ_min = 2.4°
14119 measured reflections	h = −5→7
2813 independent reflections	k = −23→23
1889 reflections with I > 2σ(I)	l = −15→14

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.064	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.177	H-atom parameters constrained
S = 1.09	w = 1/[σ²(F_o²) + (0.1P)²] where P = (F_o² + 2F_c²)/3
2813 reflections	(Δ/σ)_max < 0.001
146 parameters	Δρ_max = 0.27 e Å⁻³
0 restraints	Δρ_min = −0.30 e Å⁻³

Special details top

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

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

	x	y	z	U_iso*/U_eq
O1	0.1048 (2)	0.62026 (7)	0.20002 (11)	0.0221 (4)
O3	−0.4360 (3)	0.73867 (7)	0.01862 (12)	0.0230 (4)
O2	−0.6161 (2)	0.62208 (7)	−0.01700 (11)	0.0243 (4)
C10	−0.4499 (3)	0.66119 (10)	0.02530 (16)	0.0184 (4)
C6	0.1914 (3)	0.48387 (10)	0.22525 (16)	0.0181 (4)
N1	−0.0666 (3)	0.67215 (8)	0.14685 (14)	0.0225 (4)
C4	0.5520 (4)	0.44302 (11)	0.34137 (19)	0.0256 (5)
H4	0.692513	0.455560	0.387897	0.031*
C7	0.0322 (4)	0.54579 (9)	0.17410 (16)	0.0174 (4)
C9	−0.2320 (3)	0.62718 (10)	0.09196 (15)	0.0180 (4)
C5	0.4000 (4)	0.50161 (10)	0.29503 (17)	0.0234 (5)
H5	0.438869	0.553372	0.311094	0.028*
C3	0.4941 (4)	0.36559 (11)	0.31817 (17)	0.0249 (5)
H3	0.596502	0.326217	0.348598	0.030*
C1	0.1308 (4)	0.40540 (10)	0.20262 (16)	0.0203 (4)
H1	−0.010182	0.392615	0.156628	0.024*
C12	−0.5855 (4)	0.86283 (11)	−0.04174 (18)	0.0273 (5)
H12A	−0.579681	0.880375	0.035929	0.041*
H12B	−0.711938	0.890614	−0.086440	0.041*
H12C	−0.429204	0.872225	−0.071751	0.041*
C8	−0.1780 (3)	0.54715 (9)	0.10639 (16)	0.0185 (4)
H8	−0.267753	0.504983	0.075862	0.022*
C11	−0.6410 (4)	0.77721 (11)	−0.04635 (18)	0.0243 (5)
H11A	−0.794720	0.766468	−0.012878	0.029*
H11B	−0.654755	0.759053	−0.124690	0.029*
C2	0.2846 (4)	0.34724 (10)	0.24996 (17)	0.0237 (5)
H2	0.245566	0.295307	0.235394	0.028*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O1	0.0236 (8)	0.0114 (6)	0.0300 (8)	0.0009 (5)	−0.0065 (6)	0.0016 (5)
O3	0.0239 (8)	0.0128 (6)	0.0314 (8)	0.0024 (5)	−0.0047 (6)	0.0009 (5)
O2	0.0233 (8)	0.0170 (6)	0.0319 (8)	−0.0022 (5)	−0.0028 (6)	−0.0018 (6)
C10	0.0199 (10)	0.0140 (8)	0.0215 (10)	−0.0001 (7)	0.0026 (8)	−0.0025 (7)
C6	0.0190 (10)	0.0150 (8)	0.0207 (10)	0.0016 (7)	0.0047 (8)	0.0019 (7)
N1	0.0246 (10)	0.0139 (7)	0.0280 (9)	0.0031 (6)	−0.0052 (7)	0.0029 (7)
C4	0.0195 (11)	0.0220 (10)	0.0345 (12)	−0.0005 (8)	−0.0036 (8)	0.0034 (8)
C7	0.0234 (11)	0.0102 (8)	0.0190 (10)	−0.0019 (7)	0.0041 (8)	−0.0019 (7)
C9	0.0209 (10)	0.0131 (8)	0.0204 (10)	−0.0019 (7)	0.0035 (8)	0.0001 (7)
C5	0.0211 (11)	0.0146 (9)	0.0345 (12)	−0.0003 (7)	0.0017 (9)	0.0006 (8)
C3	0.0224 (11)	0.0195 (9)	0.0331 (11)	0.0057 (8)	0.0038 (9)	0.0064 (8)
C1	0.0218 (11)	0.0161 (8)	0.0228 (10)	−0.0003 (7)	0.0005 (8)	−0.0010 (7)
C12	0.0294 (12)	0.0197 (9)	0.0320 (12)	0.0047 (8)	−0.0019 (9)	0.0042 (8)
C8	0.0208 (10)	0.0108 (8)	0.0243 (10)	−0.0014 (7)	0.0032 (8)	−0.0020 (7)
C11	0.0219 (11)	0.0197 (9)	0.0300 (11)	0.0041 (8)	−0.0055 (8)	0.0009 (8)
C2	0.0276 (11)	0.0150 (8)	0.0289 (11)	0.0020 (8)	0.0042 (8)	−0.0001 (8)

Geometric parameters (Å, º) top

O1—C7	1.366 (2)	C9—C8	1.413 (2)
O1—N1	1.4018 (19)	C5—H5	0.9300
O3—C10	1.336 (2)	C3—C2	1.379 (3)
O3—C11	1.461 (2)	C3—H3	0.9300
O2—C10	1.203 (2)	C1—C2	1.391 (3)
C10—C9	1.489 (3)	C1—H1	0.9300
C6—C5	1.382 (3)	C12—C11	1.502 (2)
C6—C1	1.408 (2)	C12—H12A	0.9600
C6—C7	1.471 (2)	C12—H12B	0.9600
N1—C9	1.317 (2)	C12—H12C	0.9600
C4—C3	1.389 (3)	C8—H8	0.9300
C4—C5	1.387 (3)	C11—H11A	0.9700
C4—H4	0.9300	C11—H11B	0.9700
C7—C8	1.342 (3)	C2—H2	0.9300

C7—O1—N1	108.98 (13)	C4—C3—H3	120.1
C10—O3—C11	115.97 (14)	C2—C1—C6	119.14 (18)
O2—C10—O3	125.19 (16)	C2—C1—H1	120.4
O2—C10—C9	122.75 (16)	C6—C1—H1	120.4
O3—C10—C9	112.06 (15)	C11—C12—H12A	109.5
C5—C6—C1	119.53 (17)	C11—C12—H12B	109.5
C5—C6—C7	120.93 (16)	H12A—C12—H12B	109.5
C1—C6—C7	119.54 (17)	C11—C12—H12C	109.5
C9—N1—O1	104.55 (14)	H12A—C12—H12C	109.5
C3—C4—C5	119.89 (19)	H12B—C12—H12C	109.5
C3—C4—H4	120.1	C9—C8—C7	104.35 (15)
C5—C4—H4	120.1	C9—C8—H8	127.8
O1—C7—C8	109.53 (15)	C7—C8—H8	127.8
O1—C7—C6	115.78 (16)	O3—C11—C12	106.35 (15)
C8—C7—C6	134.68 (16)	O3—C11—H11A	110.5
C8—C9—N1	112.59 (16)	C12—C11—H11A	110.5
C8—C9—C10	126.49 (16)	O3—C11—H11B	110.5
N1—C9—C10	120.92 (15)	C12—C11—H11B	110.5
C6—C5—C4	120.69 (17)	H11A—C11—H11B	108.7
C6—C5—H5	119.7	C3—C2—C1	120.87 (17)
C4—C5—H5	119.7	C3—C2—H2	119.6
C2—C3—C4	119.87 (18)	C1—C2—H2	119.6
C2—C3—H3	120.1

C11—O3—C10—O2	−0.4 (3)	O3—C10—C9—N1	7.3 (2)
C11—O3—C10—C9	179.40 (15)	C1—C6—C5—C4	1.1 (3)
C7—O1—N1—C9	−0.10 (19)	C7—C6—C5—C4	−178.82 (18)
N1—O1—C7—C8	0.15 (19)	C3—C4—C5—C6	−0.4 (3)
N1—O1—C7—C6	−179.04 (15)	C5—C4—C3—C2	−0.6 (3)
C5—C6—C7—O1	0.1 (3)	C5—C6—C1—C2	−0.9 (3)
C1—C6—C7—O1	−179.73 (15)	C7—C6—C1—C2	179.02 (17)
C5—C6—C7—C8	−178.8 (2)	N1—C9—C8—C7	0.1 (2)
C1—C6—C7—C8	1.3 (3)	C10—C9—C8—C7	−178.89 (17)
O1—N1—C9—C8	0.0 (2)	O1—C7—C8—C9	−0.13 (19)
O1—N1—C9—C10	179.04 (15)	C6—C7—C8—C9	178.9 (2)
O2—C10—C9—C8	6.0 (3)	C10—O3—C11—C12	179.89 (15)
O3—C10—C9—C8	−173.78 (16)	C4—C3—C2—C1	0.8 (3)
O2—C10—C9—N1	−172.86 (18)	C6—C1—C2—C3	0.0 (3)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C1—H1···O2ⁱ	0.93	2.52	3.447 (2)	171
C8—H8···O2ⁱ	0.93	2.36	3.260 (2)	163

Symmetry code: (i) −x−1, −y+1, −z.

Acknowledgements

SK is grateful for a Ramanujan Fellowship. VT and AS thank the IIT Gandhinagar for laboratory facilities and infrastructure. The authors thank the IISER Bhopal for the SCXRD facility.

References

Bastos, C. M., Munoz, B. & Tait, B. (2015). WO2015138909 A1. PCT/US2015/020460, US Patent. Google Scholar
Bruker (2006). APEX2 and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Conti, P., De Amici, M., Grazioso, G., Roda, G., Pinto, A., Hansen, K. B., Nielsen, B., Madsen, U., Bräuner-Osborne, H., Egebjerg, J., Vestri, V., Pellegrini-Giampietro, D. E., Sibille, P., Acher, F. C. & De Micheli, C. (2005). J. Med. Chem. 48, 6315–6325. Web of Science CrossRef PubMed CAS Google Scholar
Dadiboyena, S. & Nefzi, A. (2010). Eur. J. Med. Chem. 45, 4697–4707. Web of Science CrossRef CAS PubMed Google Scholar
Dou, G., Xu, P., Li, Q., Xi, Y., Huang, Z. & Shi, D. (2013). Molecules, 18, 13645–13653. Web of Science CrossRef CAS PubMed Google Scholar
Groom, C. R., Bruno, I. J., Lightfoot, M. P. & Ward, S. C. (2016). Acta Cryst. B72, 171–179. Web of Science CSD CrossRef IUCr Journals Google Scholar
Macrae, C. F., Bruno, I. J., Chisholm, J. A., Edgington, P. R., McCabe, P., Pidcock, E., Rodriguez-Monge, L., Taylor, R., van de Streek, J. & Wood, P. A. (2008). J. Appl. Cryst. 41, 466–470. Web of Science CSD CrossRef CAS IUCr Journals Google Scholar
McKinnon, J. J., Jayatilaka, D. & Spackman, M. A. (2007). Chem. Commun. pp. 3814–3816. Web of Science CrossRef Google Scholar
McKinnon, J. J., Spackman, M. A. & Mitchell, A. S. (2004). Acta Cryst. B60, 627–668. Web of Science CrossRef CAS IUCr Journals Google Scholar
Panda, S. S., Chowdary, P. V. R. & Jayashree, B. S. (2009). Indian J. Pharm. Sci. 71, 684–687. CrossRef CAS PubMed 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
Spackman, M. A. & Jayatilaka, D. (2009). CrystEngComm, 11, 19–32. Web of Science CrossRef CAS Google Scholar
Spackman, M. A. & McKinnon, J. J. (2002). CrystEngComm, 4, 378–392. Web of Science CrossRef CAS Google Scholar
Srivastava, S., Bajpai, L. K., Batra, S., Bhaduri, A. P., Maikhuri, J. P., Gupta, G. & Dhar, J. D. (1999). Bioorg. Med. Chem. 7, 2607–2613. Web of Science CrossRef PubMed CAS Google Scholar
Tourteau, A., Andrzejak, V., Body-Malapel, M., Lemaire, L., Lemoine, A., Mansouri, R., Djouina, M., Renault, N., El Bakali, J., Desreumaux, P., Muccioli, G. G., Lambert, D. M., Chavatte, P., Rigo, B., Leleu-Chavain, N. & Millet, R. (2013). Bioorg. Med. Chem. 21, 5383–5394. Web of Science CrossRef CAS PubMed Google Scholar
Waldo, J. P. & Larock, R. C. (2007). J. Org. Chem. 72, 9643–9647. Web of Science CrossRef PubMed CAS Google Scholar
Zhao, J.-T., Qi, J.-J., Zhou, Y.-J., Lv, J.-G. & Zhu, J. (2012). Acta Cryst. E68, o1111. CSD CrossRef IUCr Journals 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.