5-Dimethyl­amino-N,N-dimethyl-2-nitro­benzamide

Fun, H.-K.; Jebas, S.R.; Chandrakantha, B.; Padmar, V.; Isloor, A.M.

doi:10.1107/S1600536809018017

organic compounds

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 65| Part 6| June 2009| Page o1342

doi:10.1107/S1600536809018017

Open

access

5-Dimethylamino-N,N-dimethyl-2-nitrobenzamide

Hoong-Kun Fun,^a ^*‡ Samuel Robinson Jebas,^a § B. Chandrakantha,^b Vijaya Padmar ^c and Arun M Isloor ^c

^aX-ray Crystallography Unit, School of Physics, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia, ^bManipal Institute of Technology, Manipal University, Manipal 576 104, India, and ^cDepartment of Chemistry, National Institute of Technology-Karnataka, Surathkal, Mangalore 575 025, India
^*Correspondence e-mail: hkfun@usm.my

(Received 6 May 2009; accepted 13 May 2009; online 20 May 2009)

In the title compound, C₁₁H₁₅N₃O₃, one of the methyl groups attached to the benzamide unit is slightly twisted with a C—N—C—C torsion angle of 4.04 (13)°. The crystal packing is stabilized by weak intermolecular C—H⋯O hydrogen bonds together with a weak C—H⋯π interaction.

Related literature

For nitroaniline mustards, see: Brian et al. (1992 ); Rauth, (1984 ). For N-[(N,N-dimethylamino)ethyl]carboxamide derivatives, see: Alston et al. (1983 ); Denny & Wilson (1986 ); Palmer et al. (1990 ). For bond-length data, see: Allen et al. (1987 ). For the stability of the temperature controller used in the data collection, see: Cosier & Glazer (1986 ).

Experimental

Crystal data

C₁₁H₁₅N₃O₃
M_r = 237.26
Monoclinic, P 2₁
a = 7.8581 (2) Å
b = 7.2921 (2) Å
c = 10.5183 (3) Å
β = 104.663 (1)°
V = 583.09 (3) Å³
Z = 2
Mo Kα radiation
μ = 0.10 mm⁻¹
T = 100 K
0.52 × 0.45 × 0.33 mm

Data collection

Bruker SMART APEXII CCD area-detector diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2005 ) T_min = 0.949, T_max = 0.965
16075 measured reflections
3233 independent reflections
3002 reflections with I > 2σ(I)
R_int = 0.027

Refinement

R[F² > 2σ(F²)] = 0.038
wR(F²) = 0.103
S = 1.08
3233 reflections
158 parameters
1 restraint
H-atom parameters constrained
Δρ_max = 0.64 e Å⁻³
Δρ_min = −0.19 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C8—H8A⋯O3ⁱ	0.96	2.52	3.1751 (16)	126
C10—H10A⋯O2ⁱⁱ	0.96	2.59	3.5413 (14)	173
C10—H10B⋯O1ⁱⁱⁱ	0.96	2.49	3.3920 (13)	156
C4—H4A⋯Cg1^iv	0.93	2.81	3.3991 (11)	122
Symmetry codes: (i) $[-x+1, y+{\script{1\over 2}}, -z+1]$ ; (ii) x-1, y, z; (iii) $[-x, y-{\script{1\over 2}}, -z]$ ; (iv) $[-x+1, y-{\script{1\over 2}}, -z]$ . Cg1 is the centroid of the C1–C6 ring.

Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008 ); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009 ).

Supporting information

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536809018017/dn2453sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536809018017/dn2453Isup2.hkl

checkCIF report

Comment top

Nitroaniline mustards are potential hypoxia-selective cytotoxic agents (Rauth, 1984) possessing reductive metabolism which activates the mustard nitrogen by converting the electron-withdrawing nitro group to an electron-donating hydroxylamine or amine (Brian et al., 1992). N-[(N,N-dimethylamino)ethyl]carboxamide derivatives proved to have excellent aqueous solubility and improved cytotoxic potency (Denny et al., 1986), but their reduction potentials, while higher than the non carboxamide compounds, were still low and have limited selectivity for hypoxic cells. (Palmer et al., 1990; Alston et al., 1983). These properties prompted us to synthesize the title compound.

In the asymmetric unit of (I), (Fig 1), one of the methyl group attached to the benzamide unit is slightly twisted as indicated by the torsion angle of C9–N1–C7–C6=4.04 (13)°. The benzene ring is essentially planar with the maximum deviation from planarity of 0.0117 (10)Å for the atom C5. The bond lengths and bond angles are normal (Allen et al., 1987).

The crystal packing is stabilized by intermolecular weak C—H···O hydrogen bonds together with weak C—H···π interaction (Table 1, Fig. 2).

Related literature top

For nitroaniline mustards, see: Brian et al. (1992); Rauth, (1984). For N-[(N,N-dimethylamino)ethyl]carboxamide derivatives, see: Alston et al. (1983); Denny et al. (1986); Palmer et al. (1990). For related bond-length data, see: Allen et al. (1987). For the stability of the temperature controller used in the data collection, see: Cosier & Glazer (1986). Cg1 is the centroid of the C1–C6 ring.

Experimental top

5-Fluoro-2-nitrobenzoic acid (5 g, 0.0270 mol) was heated with 40% aqueous dimethyl amine solution (50 ml) at 100°C for 18 hrs. Reaction mixture was concentrated through rotovap using high vacuum pump to afford 5-(dimethylamino)-2-nitrobenzoic acid as yellow crystalline solid (4.5 g). To a solution of 5-(dimethylamino)-2-nitrobenzoic acid (4 g, 0.019 mol) in DMF(40 ml) was added 1-(3-Dimethylaminopropyl)-3-ethyl carbodiimide hydrochloride (5.4 g, 0.0285 mol), 1-hydroxy benzotriazole (0.25 g, 0.0019 mol) and N,N-diisopropyl ethylamine (4.9 g, 0.038 mol) and the reaction mixture was stirred at room temperature for 18 hrs. Reaction mixture was portioned between 10% sodium bicarbonate solution and ethyl acetate (25 ml). The organic layer was washed with brine and dried over anhydrous sodium sulfate and concentrated through rotovap. The concentrated product were purified by column chromatography (60–120 mesh silica gel) using hexane and ethyl acetate as eluent to afford 5-(dimethylamino)-N, N-dimethyl-2-nitrobenzamide (3 g, 66.6%) as yellow crystalline solid. M.p was found to be 458–461 K.

Computing details top

Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT (Bruker, 2005); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009).

Figures top

	Fig. 1. The molecular structure of the title compound, showing 50% probability displacement ellipsoids and the atom numbering scheme.
	Fig. 2. The crystal packing of the title compound, viewed along the a axis. Dashed lines indicate the hydrogen bonding and C-H···π interactions.

(I) top

Crystal data top

C₁₁H₁₅N₃O₃	F(000) = 252
M_r = 237.26	D_x = 1.351 Mg m⁻³
Monoclinic, P2₁	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2yb	Cell parameters from 9204 reflections
a = 7.8581 (2) Å	θ = 2.7–40.5°
b = 7.2921 (2) Å	µ = 0.10 mm⁻¹
c = 10.5183 (3) Å	T = 100 K
β = 104.663 (1)°	Block, yellow
V = 583.09 (3) Å³	0.52 × 0.45 × 0.33 mm
Z = 2

Data collection top

Bruker SMART APEXII CCD area-detector diffractometer	3233 independent reflections
Radiation source: fine-focus sealed tube	3002 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.027
ϕ and ω scans	θ_max = 37.5°, θ_min = 2.7°
Absorption correction: multi-scan (SADABS; Bruker, 2005)	h = −13→13
T_min = 0.949, T_max = 0.965	k = −12→12
16075 measured reflections	l = −18→18

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)] = 0.038	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.103	H-atom parameters constrained
S = 1.08	w = 1/[σ²(F_o²) + (0.0716P)² + 0.0071P] where P = (F_o² + 2F_c²)/3
3233 reflections	(Δ/σ)_max < 0.001
158 parameters	Δρ_max = 0.64 e Å⁻³
1 restraint	Δρ_min = −0.19 e Å⁻³

Crystal data top

C₁₁H₁₅N₃O₃	V = 583.09 (3) Å³
M_r = 237.26	Z = 2
Monoclinic, P2₁	Mo Kα radiation
a = 7.8581 (2) Å	µ = 0.10 mm⁻¹
b = 7.2921 (2) Å	T = 100 K
c = 10.5183 (3) Å	0.52 × 0.45 × 0.33 mm
β = 104.663 (1)°

Data collection top

Bruker SMART APEXII CCD area-detector diffractometer	3233 independent reflections
Absorption correction: multi-scan (SADABS; Bruker, 2005)	3002 reflections with I > 2σ(I)
T_min = 0.949, T_max = 0.965	R_int = 0.027
16075 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.038	1 restraint
wR(F²) = 0.103	H-atom parameters constrained
S = 1.08	Δρ_max = 0.64 e Å⁻³
3233 reflections	Δρ_min = −0.19 e Å⁻³
158 parameters

Special details top

Experimental. The crystal was placed in the cold stream of an Oxford Cyrosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.

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
O1	0.42663 (10)	1.04274 (10)	0.31204 (7)	0.01969 (13)
O2	0.81992 (10)	0.62755 (17)	0.20077 (10)	0.0334 (2)
O3	0.71314 (10)	0.76718 (13)	0.34531 (8)	0.02322 (15)
N1	0.32548 (10)	0.78907 (13)	0.39646 (8)	0.01811 (14)
N2	0.03825 (10)	0.70383 (12)	−0.13123 (8)	0.01594 (13)
N3	0.69532 (10)	0.69824 (13)	0.23538 (9)	0.01899 (15)
C1	0.21826 (10)	0.78067 (12)	0.08485 (8)	0.01443 (13)
H1A	0.1210	0.8309	0.1072	0.017*
C2	0.19805 (10)	0.70835 (12)	−0.04364 (9)	0.01396 (13)
C3	0.35014 (11)	0.63797 (13)	−0.07614 (9)	0.01687 (15)
H3A	0.3427	0.5950	−0.1606	0.020*
C4	0.50889 (12)	0.63311 (14)	0.01717 (10)	0.01789 (16)
H4A	0.6070	0.5837	−0.0045	0.021*
C5	0.52463 (11)	0.70133 (13)	0.14373 (9)	0.01538 (14)
C6	0.37880 (10)	0.77846 (12)	0.17780 (8)	0.01392 (13)
C7	0.38381 (11)	0.87931 (13)	0.30423 (8)	0.01530 (14)
C8	0.30516 (14)	0.88622 (18)	0.51258 (10)	0.02438 (19)
H8A	0.3409	1.0116	0.5088	0.037*
H8B	0.3770	0.8290	0.5899	0.037*
H8C	0.1842	0.8822	0.5156	0.037*
C9	0.26858 (13)	0.59813 (16)	0.38621 (11)	0.02241 (18)
H9A	0.3149	0.5368	0.3215	0.034*
H9B	0.1424	0.5930	0.3606	0.034*
H9C	0.3109	0.5389	0.4698	0.034*
C10	−0.11334 (12)	0.79019 (15)	−0.10016 (10)	0.02084 (17)
H10A	−0.1220	0.7503	−0.0151	0.031*
H10B	−0.2183	0.7562	−0.1650	0.031*
H10C	−0.0997	0.9210	−0.0999	0.031*
C11	0.02302 (13)	0.65472 (17)	−0.26808 (10)	0.02261 (18)
H11A	0.0664	0.5324	−0.2724	0.034*
H11B	0.0908	0.7388	−0.3056	0.034*
H11C	−0.0982	0.6607	−0.3163	0.034*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O1	0.0221 (3)	0.0166 (3)	0.0198 (3)	−0.0026 (2)	0.0044 (2)	−0.0016 (2)
O2	0.0152 (3)	0.0482 (6)	0.0356 (4)	0.0109 (3)	0.0039 (3)	−0.0048 (4)
O3	0.0180 (3)	0.0286 (4)	0.0212 (3)	−0.0001 (3)	0.0016 (2)	0.0009 (3)
N1	0.0175 (3)	0.0211 (4)	0.0163 (3)	−0.0025 (3)	0.0053 (2)	0.0010 (3)
N2	0.0142 (3)	0.0169 (3)	0.0162 (3)	0.0002 (2)	0.0029 (2)	−0.0020 (3)
N3	0.0132 (3)	0.0199 (3)	0.0232 (3)	0.0010 (3)	0.0033 (2)	0.0028 (3)
C1	0.0119 (3)	0.0156 (3)	0.0163 (3)	0.0001 (2)	0.0045 (2)	−0.0015 (3)
C2	0.0134 (3)	0.0125 (3)	0.0162 (3)	−0.0006 (2)	0.0042 (2)	−0.0005 (3)
C3	0.0154 (3)	0.0165 (3)	0.0198 (4)	0.0002 (3)	0.0065 (3)	−0.0033 (3)
C4	0.0142 (3)	0.0175 (4)	0.0230 (4)	0.0013 (3)	0.0065 (3)	−0.0022 (3)
C5	0.0117 (3)	0.0151 (3)	0.0191 (3)	0.0008 (3)	0.0036 (2)	0.0010 (3)
C6	0.0128 (3)	0.0134 (3)	0.0159 (3)	−0.0007 (2)	0.0043 (2)	0.0011 (3)
C7	0.0131 (3)	0.0175 (3)	0.0150 (3)	−0.0004 (3)	0.0029 (2)	0.0003 (3)
C8	0.0253 (4)	0.0322 (5)	0.0174 (4)	0.0020 (4)	0.0086 (3)	0.0002 (4)
C9	0.0205 (4)	0.0228 (4)	0.0232 (4)	−0.0045 (3)	0.0041 (3)	0.0059 (3)
C10	0.0145 (3)	0.0253 (4)	0.0214 (4)	0.0033 (3)	0.0020 (3)	−0.0045 (4)
C11	0.0208 (4)	0.0303 (5)	0.0164 (3)	−0.0019 (3)	0.0040 (3)	−0.0045 (3)

Geometric parameters (Å, º) top

O1—C7	1.2354 (12)	C4—C5	1.3969 (13)
O2—N3	1.2400 (12)	C4—H4A	0.9300
O3—N3	1.2358 (12)	C5—C6	1.4021 (11)
N1—C7	1.3450 (12)	C6—C7	1.5115 (13)
N1—C8	1.4553 (13)	C8—H8A	0.9600
N1—C9	1.4580 (14)	C8—H8B	0.9600
N2—C2	1.3569 (11)	C8—H8C	0.9600
N2—C10	1.4558 (12)	C9—H9A	0.9600
N2—C11	1.4585 (12)	C9—H9B	0.9600
N3—C5	1.4403 (12)	C9—H9C	0.9600
C1—C6	1.3868 (11)	C10—H10A	0.9600
C1—C2	1.4216 (12)	C10—H10B	0.9600
C1—H1A	0.9300	C10—H10C	0.9600
C2—C3	1.4197 (11)	C11—H11A	0.9600
C3—C4	1.3787 (12)	C11—H11B	0.9600
C3—H3A	0.9300	C11—H11C	0.9600

C7—N1—C8	119.80 (9)	O1—C7—N1	124.11 (9)
C7—N1—C9	124.61 (8)	O1—C7—C6	118.29 (8)
C8—N1—C9	115.48 (8)	N1—C7—C6	117.31 (8)
C2—N2—C10	120.41 (7)	N1—C8—H8A	109.5
C2—N2—C11	120.45 (7)	N1—C8—H8B	109.5
C10—N2—C11	117.41 (8)	H8A—C8—H8B	109.5
O3—N3—O2	122.21 (9)	N1—C8—H8C	109.5
O3—N3—C5	119.06 (8)	H8A—C8—H8C	109.5
O2—N3—C5	118.74 (9)	H8B—C8—H8C	109.5
C6—C1—C2	121.92 (7)	N1—C9—H9A	109.5
C6—C1—H1A	119.0	N1—C9—H9B	109.5
C2—C1—H1A	119.0	H9A—C9—H9B	109.5
N2—C2—C3	121.23 (8)	N1—C9—H9C	109.5
N2—C2—C1	121.07 (7)	H9A—C9—H9C	109.5
C3—C2—C1	117.69 (7)	H9B—C9—H9C	109.5
C4—C3—C2	120.20 (8)	N2—C10—H10A	109.5
C4—C3—H3A	119.9	N2—C10—H10B	109.5
C2—C3—H3A	119.9	H10A—C10—H10B	109.5
C3—C4—C5	121.00 (8)	N2—C10—H10C	109.5
C3—C4—H4A	119.5	H10A—C10—H10C	109.5
C5—C4—H4A	119.5	H10B—C10—H10C	109.5
C4—C5—C6	120.36 (8)	N2—C11—H11A	109.5
C4—C5—N3	118.37 (7)	N2—C11—H11B	109.5
C6—C5—N3	121.20 (8)	H11A—C11—H11B	109.5
C1—C6—C5	118.75 (8)	N2—C11—H11C	109.5
C1—C6—C7	115.54 (7)	H11A—C11—H11C	109.5
C5—C6—C7	125.39 (7)	H11B—C11—H11C	109.5

C10—N2—C2—C3	−174.89 (9)	C2—C1—C6—C5	−0.44 (13)
C11—N2—C2—C3	−10.25 (14)	C2—C1—C6—C7	173.36 (8)
C10—N2—C2—C1	6.32 (14)	C4—C5—C6—C1	1.86 (13)
C11—N2—C2—C1	170.96 (9)	N3—C5—C6—C1	178.85 (8)
C6—C1—C2—N2	176.85 (9)	C4—C5—C6—C7	−171.28 (9)
C6—C1—C2—C3	−1.98 (13)	N3—C5—C6—C7	5.71 (14)
N2—C2—C3—C4	−175.78 (9)	C8—N1—C7—O1	1.74 (14)
C1—C2—C3—C4	3.05 (13)	C9—N1—C7—O1	177.67 (9)
C2—C3—C4—C5	−1.73 (15)	C8—N1—C7—C6	−171.90 (8)
C3—C4—C5—C6	−0.79 (15)	C9—N1—C7—C6	4.04 (13)
C3—C4—C5—N3	−177.86 (9)	C1—C6—C7—O1	−91.10 (10)
O3—N3—C5—C4	176.11 (9)	C5—C6—C7—O1	82.24 (12)
O2—N3—C5—C4	−3.35 (14)	C1—C6—C7—N1	82.91 (10)
O3—N3—C5—C6	−0.94 (14)	C5—C6—C7—N1	−103.75 (10)
O2—N3—C5—C6	179.61 (10)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C8—H8A···O3ⁱ	0.96	2.52	3.1751 (16)	126
C10—H10A···O2ⁱⁱ	0.96	2.59	3.5413 (14)	173
C10—H10B···O1ⁱⁱⁱ	0.96	2.49	3.3920 (13)	156
C4—H4A···Cg1^iv	0.93	2.81	3.3991 (11)	122

Symmetry codes: (i) −x+1, y+1/2, −z+1; (ii) x−1, y, z; (iii) −x, y−1/2, −z; (iv) −x+1, y−1/2, −z.

Experimental details

Crystal data
Chemical formula	C₁₁H₁₅N₃O₃
M_r	237.26
Crystal system, space group	Monoclinic, P2₁
Temperature (K)	100
a, b, c (Å)	7.8581 (2), 7.2921 (2), 10.5183 (3)
β (°)	104.663 (1)
V (Å³)	583.09 (3)
Z	2
Radiation type	Mo Kα
µ (mm⁻¹)	0.10
Crystal size (mm)	0.52 × 0.45 × 0.33

Data collection
Diffractometer	Bruker SMART APEXII CCD area-detector diffractometer
Absorption correction	Multi-scan (SADABS; Bruker, 2005)
T_min, T_max	0.949, 0.965
No. of measured, independent and observed [I > 2σ(I)] reflections	16075, 3233, 3002
R_int	0.027
(sin θ/λ)_max (Å⁻¹)	0.857

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.038, 0.103, 1.08
No. of reflections	3233
No. of parameters	158
No. of restraints	1
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.64, −0.19

Computer programs: APEX2 (Bruker, 2005), SAINT (Bruker, 2005), SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C8—H8A···O3ⁱ	0.96	2.52	3.1751 (16)	126
C10—H10A···O2ⁱⁱ	0.96	2.59	3.5413 (14)	173
C10—H10B···O1ⁱⁱⁱ	0.96	2.49	3.3920 (13)	156
C4—H4A···Cg1^iv	0.93	2.81	3.3991 (11)	122

Symmetry codes: (i) −x+1, y+1/2, −z+1; (ii) x−1, y, z; (iii) −x, y−1/2, −z; (iv) −x+1, y−1/2, −z.

Footnotes

‡Thomson Reuters Researcher ID: A-3561-2009.

§Thomson Reuters Researcher ID: A-5473-2009. Permanent address: Department of Physics, Karunya University, Karunya Nagar, Coimbatore 641 114, India.

Acknowledgements

HKF and SRJ thank the Malaysian Government and Universiti Sains Malaysia for the Science Fund grant No. 305/PFIZIK/613312. SRJ thanks Universiti Sains Malaysia for a post–doctoral research fellowship. HKF also thanks Universiti Sains Malaysia for the Research University Golden Goose grant No. 1001/PFIZIK/811012. AMI is grateful to the Head of the Chemistry Department and the Director, NITK, Surathkal, India, for providing research facilities.

References

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. CrossRef Web of Science Google Scholar
Alston, T. A., Porter, D. J. & Bright, H. J. (1983). Acc. Chem. Res. 16, 418–442. CrossRef CAS Web of Science Google Scholar
Brian, D. P., William, R. W., Stephen, C. & William, A. D. (1992). J. Med. Chem. 35, 3214–3222. PubMed Web of Science Google Scholar
Bruker (2005). APEX2, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Cosier, J. & Glazer, A. M. (1986). J. Appl. Cryst. 19, 105–107. CrossRef CAS Web of Science IUCr Journals Google Scholar
Denny, W. A. & Wilson, W. R. (1986). J. Med. Chem. 29, 879–887. CrossRef CAS PubMed Web of Science Google Scholar
Palmer, B. D., Wilson, W. R., Pullen, S. M. & Denny, W. A. (1990). J. Med. Chem. 33, 112–121. CrossRef CAS PubMed Web of Science Google Scholar
Rauth, A. M. (1984). Oncol. Biol. Phys. 10, 1293–1300. CrossRef CAS Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Spek, A. L. (2009). Acta Cryst. D65, 148–155. Web of Science CrossRef CAS IUCr Journals Google Scholar