4,7-Dichloro­quinoline

Kulkarni, A.A.; King, C.; Butcher, R.J.; Fortunak, J.M.D.

doi:10.1107/S1600536812014924

organic compounds

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 68| Part 5| May 2012| Page o1498

doi:10.1107/S1600536812014924

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4,7-Dichloroquinoline

Amol A. Kulkarni,^a ^* Christopher King,^b Ray J. Butcher ^b and Joseph M. D. Fortunak ^b

^aCollege of Pharmacy, Howard University, 2300 4th Street, NW, Washington, DC 2059, USA, and ^bDepartment of Chemistry, Howard University, 525 College Street, NW, Washington, DC 2059, USA
^*Correspondence e-mail: amol.kulkarni@howard.edu

(Received 27 February 2012; accepted 4 April 2012; online 21 April 2012)

The two molecules in the asymmetric unit of the title compound, C₉H₅Cl₂N, are both essentially planar (r.m.s. deviations for all non-H atoms = 0.014 and 0.026 Å). There are no close C—H⋯Cl contacts.

Related literature

4,7-dichloroquinoline is a commonly used starting material for the synthesis of a variety of anti-malarial drugs, such as amodiquine {systematic name: 4-[(7-chloroquinolin-4-yl)amino]-2-[(diethylamino)methyl]phenol}, see: Dongre et al. (2007 ); O'Neill et al. (2003 ); Lawrence et al. (2008 ); Saha et al. (2009 ).

Experimental

Crystal data

C₉H₅Cl₂N
M_r = 198.04
Monoclinic, P 2₁ /n
a = 18.2243 (17) Å
b = 3.8253 (5) Å
c = 23.622 (3) Å
β = 96.61 (1)°
V = 1635.8 (4) Å³
Z = 8
Cu Kα radiation
μ = 6.59 mm⁻¹
T = 123 K
0.35 × 0.23 × 0.16 mm

Data collection

Oxford Diffraction Xcalibur Ruby Gemini diffractometer
Absorption correction: multi-scan (CrysAlis PRO; Oxford Diffraction, 2007 $[Oxford Diffraction (2007). CrysAlis PRO and CrysAlis RED. Oxford Diffraction Ltd, Abingdon, England.]$ ) T_min = 0.233, T_max = 1.000
5147 measured reflections
3188 independent reflections
2148 reflections with I > 2σ(I)
R_int = 0.090

Refinement

R[F² > 2σ(F²)] = 0.096
wR(F²) = 0.327
S = 1.08
3188 reflections
217 parameters
H-atom parameters constrained
Δρ_max = 0.68 e Å⁻³
Δρ_min = −0.49 e Å⁻³

Data collection: CrysAlis PRO (Oxford Diffraction, 2007 $[Oxford Diffraction (2007). CrysAlis PRO and CrysAlis RED. Oxford Diffraction Ltd, Abingdon, England.]$ ); cell refinement: CrysAlis PRO; data reduction: CrysAlis PRO; 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 I, global. DOI: 10.1107/S1600536812014924/bt5833sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536812014924/bt5833Isup2.hkl

Supporting information file. DOI: 10.1107/S1600536812014924/bt5833Isup3.cml

checkCIF report

Comment top

The crystal structure of 4,7-dichloroquinoline has not previously been reported. Recrystallization of 4,7-dichloroquinoline from hexane or similar hydrocarbon solvents removes low levels (1–4%) of 4,5-dichloroquinoline that are present from the manufacturing process. Impurities that arise from the presence of 4,5-dichloroquinoline in 4,7-DCQ are otherwise difficult to remove from the manufacturing process of commercial malaria drugs, including amodiaquine and piperaquine (Dongre et al., 2007).

In view of the importance of this pharmaceutically active compound its crystal structure was determined. There are two molecules in the asymmetric unit (Z' = 2) and there are no close C—H···Cl contacts.

Related literature top

4,7-dichloroquinoline is a commonly used starting material for the synthesis of a variety of anti-malarial drugs, such as amodiquine {systematic name: 4-[(7-chloroquinolin-4-yl)amino]-2-[(diethylamino)methyl]phenol}, see: Dongre et al. (2007); O'Neill et al. (2003); Lawrence et al. (2008); Saha et al. (2009).

Experimental top

Hexanes (100 ml) were transferred to an Erlenmeyer flask and heated to a gentle reflux. 4,7-Dichloroquinoline (20 g, commercially available from Sigma-Aldrich) was slowly added to hexanes and the solution was maintained at 65 °C, resulting in a colorless solution. The solution was slowly cooled to room temperature and maintained at room temperature for 12 h. Long, colorless needles were observed to slowly crystallize from solution. The colorless needles obtained were isolated by filtration and dried to a constant weight, mp 83–84 °C; ¹H-NMR (CDCl₃) d 8.78 (d, J = 4.8 Hz, 1H), 8.15 (d, J = 9.2 Hz, 1H), 8.11 (d, J = 2.4 Hz, 1H), 7.59 (dd, J = 9.2, 2.4 Hz, 1H), 7.48 (d, J = 4.8 Hz, 1H).

Computing details top

Data collection: CrysAlis PRO (Oxford Diffraction, 2007); cell refinement: CrysAlis PRO (Oxford Diffraction, 2007); data reduction: CrysAlis PRO (Oxford Diffraction, 2007); 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. A view of the title compound, C₉H₅Cl₂N, showing atom numbering scheme and the two molecules in the asymmetric unit.

4,7-Dichloroquinoline top

Crystal data top

C₉H₅Cl₂N	F(000) = 800
M_r = 198.04	D_x = 1.608 Mg m⁻³
Monoclinic, P2₁/n	Cu Kα radiation, λ = 1.54178 Å
Hall symbol: -P 2yn	Cell parameters from 1283 reflections
a = 18.2243 (17) Å	θ = 2.9–75.6°
b = 3.8253 (5) Å	µ = 6.59 mm⁻¹
c = 23.622 (3) Å	T = 123 K
β = 96.61 (1)°	Prism, colorless
V = 1635.8 (4) Å³	0.35 × 0.23 × 0.16 mm
Z = 8

Data collection top

Oxford Diffraction Xcalibur Ruby Gemini diffractometer	3188 independent reflections
Radiation source: Enhance (Cu) X-ray Source	2148 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.090
Detector resolution: 10.5081 pixels mm^-1	θ_max = 75.8°, θ_min = 2.9°
ω scans	h = −22→16
Absorption correction: multi-scan (CrysAlis PRO; Oxford Diffraction, 2007)	k = −4→4
T_min = 0.233, T_max = 1.000	l = −23→29
5147 measured reflections

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)] = 0.096	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.327	H-atom parameters constrained
S = 1.08	w = 1/[σ²(F_o²) + (0.1577P)² + 4.2615P] where P = (F_o² + 2F_c²)/3
3188 reflections	(Δ/σ)_max < 0.001
217 parameters	Δρ_max = 0.68 e Å⁻³
0 restraints	Δρ_min = −0.49 e Å⁻³

Crystal data top

C₉H₅Cl₂N	V = 1635.8 (4) Å³
M_r = 198.04	Z = 8
Monoclinic, P2₁/n	Cu Kα radiation
a = 18.2243 (17) Å	µ = 6.59 mm⁻¹
b = 3.8253 (5) Å	T = 123 K
c = 23.622 (3) Å	0.35 × 0.23 × 0.16 mm
β = 96.61 (1)°

Data collection top

Oxford Diffraction Xcalibur Ruby Gemini diffractometer	3188 independent reflections
Absorption correction: multi-scan (CrysAlis PRO; Oxford Diffraction, 2007)	2148 reflections with I > 2σ(I)
T_min = 0.233, T_max = 1.000	R_int = 0.090
5147 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.096	0 restraints
wR(F²) = 0.327	H-atom parameters constrained
S = 1.08	Δρ_max = 0.68 e Å⁻³
3188 reflections	Δρ_min = −0.49 e Å⁻³
217 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
Cl1A	0.46391 (11)	0.7593 (6)	0.94032 (9)	0.0625 (6)
Cl2A	0.31181 (11)	0.9079 (6)	0.65527 (9)	0.0630 (6)
N1A	0.5405 (3)	0.4243 (18)	0.7726 (3)	0.0560 (15)
C2A	0.5808 (4)	0.369 (2)	0.8223 (4)	0.0544 (18)
H2AA	0.6274	0.2581	0.8219	0.065*
C3A	0.5587 (4)	0.467 (2)	0.8763 (4)	0.0560 (18)
H3AA	0.5892	0.4193	0.9108	0.067*
C4A	0.4924 (4)	0.6317 (19)	0.8765 (3)	0.0501 (16)
C5A	0.3766 (4)	0.8694 (19)	0.8220 (4)	0.0544 (18)
H5AA	0.3579	0.9425	0.8560	0.065*
C6A	0.3371 (4)	0.9282 (19)	0.7711 (4)	0.0517 (17)
H6AA	0.2906	1.0420	0.7694	0.062*
C7A	0.3646 (4)	0.822 (2)	0.7200 (4)	0.0541 (18)
C8A	0.4305 (4)	0.652 (2)	0.7206 (4)	0.0531 (17)
H8AA	0.4475	0.5771	0.6860	0.064*
C9A	0.4735 (4)	0.5904 (19)	0.7737 (4)	0.0506 (16)
C10A	0.4461 (4)	0.6984 (18)	0.8250 (3)	0.0498 (16)
Cl1B	0.50197 (10)	0.9725 (5)	0.58983 (9)	0.0589 (6)
Cl2B	0.80689 (11)	0.2033 (5)	0.48184 (10)	0.0625 (6)
N1B	0.7313 (3)	0.6479 (18)	0.6687 (3)	0.0559 (16)
C2B	0.6835 (4)	0.802 (2)	0.6981 (4)	0.0569 (18)
H2BA	0.6984	0.8463	0.7373	0.068*
C3B	0.6115 (4)	0.908 (2)	0.6755 (4)	0.0527 (17)
H3BA	0.5797	1.0195	0.6991	0.063*
C4B	0.5891 (4)	0.848 (2)	0.6205 (4)	0.0528 (17)
C5B	0.6209 (4)	0.615 (2)	0.5258 (4)	0.0559 (19)
H5BA	0.5730	0.6680	0.5077	0.067*
C6B	0.6720 (4)	0.472 (2)	0.4941 (4)	0.0539 (17)
H6BA	0.6609	0.4309	0.4544	0.065*
C7B	0.7417 (4)	0.388 (2)	0.5232 (4)	0.0565 (19)
C8B	0.7602 (4)	0.439 (2)	0.5800 (4)	0.0527 (17)
H8BA	0.8074	0.3700	0.5978	0.063*
C9B	0.7092 (4)	0.5951 (19)	0.6121 (3)	0.0483 (16)
C10B	0.6378 (4)	0.6840 (19)	0.5843 (4)	0.0526 (17)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Cl1A	0.0557 (11)	0.0571 (11)	0.0757 (13)	0.0000 (8)	0.0113 (9)	−0.0010 (9)
Cl2A	0.0476 (10)	0.0611 (11)	0.0788 (13)	0.0022 (8)	0.0012 (8)	0.0029 (9)
N1A	0.036 (3)	0.050 (3)	0.082 (4)	−0.002 (3)	0.010 (3)	0.001 (3)
C2A	0.041 (4)	0.049 (4)	0.076 (5)	0.001 (3)	0.018 (3)	0.002 (3)
C3A	0.043 (4)	0.044 (4)	0.080 (5)	−0.004 (3)	0.001 (3)	0.008 (3)
C4A	0.045 (4)	0.044 (3)	0.063 (4)	−0.005 (3)	0.013 (3)	−0.005 (3)
C5A	0.041 (4)	0.038 (3)	0.086 (5)	−0.002 (3)	0.014 (3)	−0.004 (3)
C6A	0.035 (3)	0.044 (3)	0.077 (5)	−0.001 (3)	0.012 (3)	−0.001 (3)
C7A	0.039 (4)	0.045 (4)	0.078 (5)	−0.005 (3)	0.003 (3)	0.004 (3)
C8A	0.045 (4)	0.043 (4)	0.072 (5)	−0.002 (3)	0.013 (3)	−0.007 (3)
C9A	0.036 (3)	0.039 (3)	0.077 (5)	−0.004 (3)	0.011 (3)	−0.001 (3)
C10A	0.043 (4)	0.038 (3)	0.069 (4)	−0.005 (3)	0.007 (3)	−0.002 (3)
Cl1B	0.0374 (9)	0.0560 (10)	0.0837 (13)	0.0058 (7)	0.0087 (8)	0.0054 (9)
Cl2B	0.0474 (10)	0.0558 (10)	0.0875 (14)	0.0036 (8)	0.0205 (8)	−0.0008 (9)
N1B	0.038 (3)	0.049 (3)	0.080 (4)	−0.002 (3)	0.005 (3)	0.006 (3)
C2B	0.040 (4)	0.047 (4)	0.083 (5)	−0.002 (3)	0.005 (3)	0.006 (4)
C3B	0.035 (3)	0.052 (4)	0.072 (5)	−0.004 (3)	0.011 (3)	0.004 (3)
C4B	0.041 (4)	0.044 (4)	0.074 (5)	−0.005 (3)	0.012 (3)	0.011 (3)
C5B	0.041 (4)	0.050 (4)	0.075 (5)	−0.008 (3)	−0.003 (3)	0.011 (3)
C6B	0.038 (4)	0.058 (4)	0.068 (5)	−0.004 (3)	0.016 (3)	0.001 (3)
C7B	0.031 (3)	0.048 (4)	0.093 (6)	−0.003 (3)	0.018 (3)	0.005 (4)
C8B	0.034 (3)	0.044 (4)	0.081 (5)	−0.001 (3)	0.008 (3)	0.002 (3)
C9B	0.034 (3)	0.042 (3)	0.069 (4)	−0.002 (3)	0.008 (3)	0.006 (3)
C10B	0.034 (3)	0.040 (3)	0.084 (5)	−0.002 (3)	0.008 (3)	0.006 (3)

Geometric parameters (Å, º) top

Cl1A—C4A	1.720 (8)	Cl1B—C4B	1.734 (8)
Cl2A—C7A	1.742 (8)	Cl2B—C7B	1.769 (8)
N1A—C2A	1.328 (11)	N1B—C2B	1.313 (11)
N1A—C9A	1.379 (10)	N1B—C9B	1.368 (10)
C2A—C3A	1.432 (12)	C2B—C3B	1.418 (11)
C2A—H2AA	0.9500	C2B—H2BA	0.9500
C3A—C4A	1.362 (11)	C3B—C4B	1.338 (12)
C3A—H3AA	0.9500	C3B—H3BA	0.9500
C4A—C10A	1.422 (11)	C4B—C10B	1.443 (11)
C5A—C6A	1.348 (12)	C5B—C6B	1.373 (12)
C5A—C10A	1.420 (11)	C5B—C10B	1.407 (12)
C5A—H5AA	0.9500	C5B—H5BA	0.9500
C6A—C7A	1.417 (12)	C6B—C7B	1.410 (11)
C6A—H6AA	0.9500	C6B—H6BA	0.9500
C7A—C8A	1.364 (11)	C7B—C8B	1.359 (12)
C8A—C9A	1.421 (11)	C8B—C9B	1.400 (11)
C8A—H8AA	0.9500	C8B—H8BA	0.9500
C9A—C10A	1.422 (11)	C9B—C10B	1.429 (10)

C2A—N1A—C9A	117.2 (8)	C2B—N1B—C9B	116.3 (7)
N1A—C2A—C3A	124.2 (7)	N1B—C2B—C3B	124.9 (8)
N1A—C2A—H2AA	117.9	N1B—C2B—H2BA	117.6
C3A—C2A—H2AA	117.9	C3B—C2B—H2BA	117.6
C4A—C3A—C2A	117.7 (7)	C4B—C3B—C2B	118.8 (8)
C4A—C3A—H3AA	121.1	C4B—C3B—H3BA	120.6
C2A—C3A—H3AA	121.1	C2B—C3B—H3BA	120.6
C3A—C4A—C10A	121.2 (8)	C3B—C4B—C10B	120.7 (7)
C3A—C4A—Cl1A	119.5 (7)	C3B—C4B—Cl1B	121.4 (6)
C10A—C4A—Cl1A	119.4 (6)	C10B—C4B—Cl1B	117.9 (6)
C6A—C5A—C10A	120.2 (8)	C6B—C5B—C10B	121.7 (7)
C6A—C5A—H5AA	119.9	C6B—C5B—H5BA	119.1
C10A—C5A—H5AA	119.9	C10B—C5B—H5BA	119.1
C5A—C6A—C7A	120.5 (7)	C5B—C6B—C7B	117.0 (8)
C5A—C6A—H6AA	119.8	C5B—C6B—H6BA	121.5
C7A—C6A—H6AA	119.8	C7B—C6B—H6BA	121.5
C8A—C7A—C6A	121.7 (8)	C8B—C7B—C6B	123.7 (7)
C8A—C7A—Cl2A	119.7 (7)	C8B—C7B—Cl2B	119.8 (6)
C6A—C7A—Cl2A	118.6 (6)	C6B—C7B—Cl2B	116.5 (7)
C7A—C8A—C9A	118.9 (8)	C7B—C8B—C9B	119.4 (7)
C7A—C8A—H8AA	120.6	C7B—C8B—H8BA	120.3
C9A—C8A—H8AA	120.6	C9B—C8B—H8BA	120.3
N1A—C9A—C8A	117.3 (8)	N1B—C9B—C8B	117.0 (7)
N1A—C9A—C10A	123.3 (7)	N1B—C9B—C10B	124.4 (7)
C8A—C9A—C10A	119.5 (7)	C8B—C9B—C10B	118.7 (7)
C4A—C10A—C5A	124.2 (8)	C5B—C10B—C9B	119.3 (7)
C4A—C10A—C9A	116.4 (7)	C5B—C10B—C4B	125.8 (7)
C5A—C10A—C9A	119.3 (7)	C9B—C10B—C4B	114.9 (7)

C9A—N1A—C2A—C3A	0.9 (12)	C9B—N1B—C2B—C3B	1.5 (12)
N1A—C2A—C3A—C4A	−1.0 (12)	N1B—C2B—C3B—C4B	0.3 (12)
C2A—C3A—C4A—C10A	1.1 (11)	C2B—C3B—C4B—C10B	−1.2 (11)
C2A—C3A—C4A—Cl1A	−179.2 (6)	C2B—C3B—C4B—Cl1B	−179.5 (6)
C10A—C5A—C6A—C7A	−0.2 (11)	C10B—C5B—C6B—C7B	1.7 (12)
C5A—C6A—C7A—C8A	1.1 (12)	C5B—C6B—C7B—C8B	0.4 (12)
C5A—C6A—C7A—Cl2A	−179.4 (6)	C5B—C6B—C7B—Cl2B	179.9 (6)
C6A—C7A—C8A—C9A	−1.7 (11)	C6B—C7B—C8B—C9B	−2.4 (12)
Cl2A—C7A—C8A—C9A	178.8 (6)	Cl2B—C7B—C8B—C9B	178.1 (6)
C2A—N1A—C9A—C8A	179.4 (7)	C2B—N1B—C9B—C8B	178.4 (7)
C2A—N1A—C9A—C10A	−0.9 (11)	C2B—N1B—C9B—C10B	−2.5 (11)
C7A—C8A—C9A—N1A	−178.8 (7)	C7B—C8B—C9B—N1B	−178.5 (7)
C7A—C8A—C9A—C10A	1.4 (11)	C7B—C8B—C9B—C10B	2.3 (11)
C3A—C4A—C10A—C5A	−179.7 (7)	C6B—C5B—C10B—C9B	−1.7 (11)
Cl1A—C4A—C10A—C5A	0.5 (10)	C6B—C5B—C10B—C4B	177.0 (7)
C3A—C4A—C10A—C9A	−1.1 (11)	N1B—C9B—C10B—C5B	−179.5 (7)
Cl1A—C4A—C10A—C9A	179.2 (5)	C8B—C9B—C10B—C5B	−0.3 (11)
C6A—C5A—C10A—C4A	178.6 (7)	N1B—C9B—C10B—C4B	1.7 (11)
C6A—C5A—C10A—C9A	0.0 (11)	C8B—C9B—C10B—C4B	−179.2 (7)
N1A—C9A—C10A—C4A	1.0 (10)	C3B—C4B—C10B—C5B	−178.5 (7)
C8A—C9A—C10A—C4A	−179.3 (7)	Cl1B—C4B—C10B—C5B	−0.1 (10)
N1A—C9A—C10A—C5A	179.7 (7)	C3B—C4B—C10B—C9B	0.3 (10)
C8A—C9A—C10A—C5A	−0.6 (10)	Cl1B—C4B—C10B—C9B	178.6 (5)

Experimental details

Crystal data
Chemical formula	C₉H₅Cl₂N
M_r	198.04
Crystal system, space group	Monoclinic, P2₁/n
Temperature (K)	123
a, b, c (Å)	18.2243 (17), 3.8253 (5), 23.622 (3)
β (°)	96.61 (1)
V (Å³)	1635.8 (4)
Z	8
Radiation type	Cu Kα
µ (mm⁻¹)	6.59
Crystal size (mm)	0.35 × 0.23 × 0.16

Data collection
Diffractometer	Oxford Diffraction Xcalibur Ruby Gemini diffractometer
Absorption correction	Multi-scan (CrysAlis PRO; Oxford Diffraction, 2007)
T_min, T_max	0.233, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections	5147, 3188, 2148
R_int	0.090
(sin θ/λ)_max (Å⁻¹)	0.629

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.096, 0.327, 1.08
No. of reflections	3188
No. of parameters	217
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.68, −0.49

Computer programs: CrysAlis PRO (Oxford Diffraction, 2007), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008).

Acknowledgements

AAK wishes to acknowledge RCMI, Howard University and the CDRD, College of Pharmacy, Howard University. RJB wishes to acknowledge the NSF–MRI program (grant CHE-0619278) for funds to purchase the diffractometer. This project was supported by grant No. D34HP16042-03-03 from the Health Resources and Services Administration (HRSA).

References

Dongre, V. G., Karmuse, P. P., Ghugare, P. D., Gupta, M., Nerurkar, B., Shaha, C. & Kumar, A. (2007). J. Pharm. Biomed. Anal. 43, 185–195. Web of Science CrossRef Google Scholar
Lawrence, R. M., Dennis, K. C., O'Neill, P. M., Hahn, D. U., Roeder, M. & Struppe, C. (2008). Org. Process Res. Dev. 12, 294–297. Web of Science CrossRef CAS Google Scholar
O'Neill, P. M., Mukhtar, A., Stocks, P. A., Randle, L. E., Hindley, S., Ward, S. A., Storr, R. C., Bickley, J. E., O'Neil, I. A., Maggs, J. L., Hughes, R. H., Winstanley, P. A., Bray, P. G. & Prak, B. K. (2003). J. Med. Chem. 46, 4993–4945. Google Scholar
Oxford Diffraction (2007). CrysAlis PRO and CrysAlis RED. Oxford Diffraction Ltd, Abingdon, England. Google Scholar
Saha, C. N., Bhattacharya, S. & Chetia, D. (2009). Int. J. ChemTech Res. 1, 322–328. CAS Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar