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Acta Cryst. (2009). E65, o2455    [ doi:10.1107/S1600536809036149 ]

Diethyl 3,4-bis(acetoxymethyl)thieno[2,3-b]thiophene-2,5-dicarboxylate

B. Gunasekaran, R. Sureshbabu, A. K. Mohanakrishnan, G. Chakkaravarthi and V. Manivannan

Abstract top

In the title compound, C18H20O8S2, the dihedral angle between the two thiophene rings is 2.33 (7)°. The methyl C atoms of the ester groups are disordered over two positions; the site-occupancy factors of the terminal methyl C atoms are 0.632 (18):0.368 (18) and 0.623 (17):0.377 (17). The molecular structure is stabilized by weak intramolecular C-H...O interactions and the crystal structure is stabilized through weak intermolecular C-H...O interactions.

Comment top

Thiophene derivatives exhibit anti-inflammatory (Graff et al., 2005; Hymete et al., 2005), anti-protozoal (Tapia et al., 2003) and antitumor (Dallemagne et al., 2003) activities. The geometric parameters of the title compound (Fig. 1) agree with the reported similar structures (Dufresne & Skene, 2008; Khan et al., 2004).

The dihedral angle between the two thiophene rings is 2.33 (7)°. The terminal C atoms of the ester groups are disordered over two positions (the site occupancies of C9 and C9A are 0.37 (2) and 0.63 (2), respectively and C18 and C18A are 0.62 (2) and 0.38 (2), respectively).

The molecular structure is stabilized by weak intramolecular C—H···O interactions and the crystal structure is through weak intermolecular C—H···O interactions. The intramolecular C17—H17C···O8 interaction generate five-membered ring, with graph set motif S(5) and C10—H10A···O2 and C13—H13B···O8 interactions generate six-membered rings, each with graph set motif S(6). The intermolecular C10—H10B···O6 interaction generates an eighteen-membered ring, with graph set motif of R22(18) (Bernstein et al., 1995).

Related literature top

For the biological activity of thiophene derivatives, see: Graff et al. (2005); Hymete et al. (2005); Tapia et al. (2003); Dallemagne et al. (2003). For related structures see: Dufresne & Skene (2008); Khan et al. (2004). For graph-set notation see: Bernstein et al. (1995).

Experimental top

To a solution of diethyl 3,4-dibromomethylthieno[2,3,-b]thiophene-2,5-dicarboxylate (2 g, 4.25 mmol) in dimethyl formamide (10 ml) was added potassium acetate (1.67 g, 17.0 mmol). The reaction mixture was allowed to stir at room temperature for 5 h under nitrogen atmosphere. The reaction mixture was poured over crushed ice (50 g) containing 1 ml of conc. HCl. The obtained solid was filtered and dried. Recrystallization from methanol afforded the compound.

Refinement top

The site occupancy factors of disordered C atoms were refined as C9 = 0.37 (2), C9A = 0.63 (2), C18 = 0.62 (2) and C18A = 0.38 (2) during anisotropic refinement. The C8—C9, C8—C9A, C17—C18 and C17—C18A bond distances were restrained to be 1.500 (1) Å. H atoms were positioned geometrically and refined using riding model with C—H = 0.97 Å and Uiso(H) = 1.2Ueq(C) for CH2, C—H = 0.96 Å and Uiso(H) = 1.5Ueq(C) for CH3.

Computing details top

Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT (Bruker, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. The molecular structure of the title compound, with atom labels and 30% probability displacement ellipsoids for non-H atoms.
[Figure 2] Fig. 2. The packing of the title compound, viewed down the C axis. Hydrogen bonds are shown as dashed lines.
Diethyl 3,4-bis(acetoxymethyl)thieno[2,3-b]thiophene-2,5-dicarboxylate top
Crystal data top
C18H20O8S2Z = 2
Mr = 428.46F(000) = 448
Triclinic, P1Dx = 1.458 Mg m−3
Hall symbol: -P 1Mo Kα radiation, λ = 0.71073 Å
a = 9.3214 (5) ÅCell parameters from 5319 reflections
b = 10.2416 (6) Åθ = 2.7–31.0°
c = 10.6622 (6) ŵ = 0.32 mm−1
α = 84.952 (3)°T = 295 K
β = 82.814 (4)°Needle, colourless
γ = 75.432 (3)°0.29 × 0.14 × 0.12 mm
V = 975.72 (9) Å3
Data collection top
Bruker Kappa APEX2 CCD
diffractometer		6686 independent reflections
Radiation source: fine-focus sealed tube4444 reflections with I > 2σ(I)
graphiteRint = 0.025
Detector resolution: 0 pixels mm-1θmax = 32.0°, θmin = 1.9°
ω and φ scansh = −13→13
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)		k = −15→13
Tmin = 0.914, Tmax = 0.963l = −15→15
25739 measured reflections
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.057Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.188H-atom parameters constrained
S = 1.04 w = 1/[σ2(Fo2) + (0.0945P)2 + 0.3857P]
where P = (Fo2 + 2Fc2)/3
6686 reflections(Δ/σ)max < 0.001
279 parametersΔρmax = 0.82 e Å−3
4 restraintsΔρmin = −0.59 e Å−3
Crystal data top
C18H20O8S2γ = 75.432 (3)°
Mr = 428.46V = 975.72 (9) Å3
Triclinic, P1Z = 2
a = 9.3214 (5) ÅMo Kα radiation
b = 10.2416 (6) ŵ = 0.32 mm−1
c = 10.6622 (6) ÅT = 295 K
α = 84.952 (3)°0.29 × 0.14 × 0.12 mm
β = 82.814 (4)°
Data collection top
Bruker Kappa APEX2 CCD
diffractometer		6686 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)		4444 reflections with I > 2σ(I)
Tmin = 0.914, Tmax = 0.963Rint = 0.025
25739 measured reflectionsθmax = 32.0°
Refinement top
R[F2 > 2σ(F2)] = 0.057H-atom parameters constrained
wR(F2) = 0.188Δρmax = 0.82 e Å−3
S = 1.04Δρmin = −0.59 e Å−3
6686 reflectionsAbsolute structure: ?
279 parametersFlack parameter: ?
4 restraintsRogers parameter: ?
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
S10.02951 (5)0.21624 (6)0.28483 (5)0.04706 (15)
S2−0.08189 (5)0.30619 (5)0.55975 (5)0.04537 (15)
O10.1876 (2)0.1299 (2)0.05271 (17)0.0747 (5)
O20.4020 (2)0.1825 (3)0.0622 (2)0.0920 (7)
O30.51977 (16)0.15799 (15)0.36366 (18)0.0544 (4)
O40.70351 (19)0.25297 (19)0.3848 (2)0.0719 (5)
O50.40617 (17)0.27623 (16)0.65075 (16)0.0533 (4)
O60.5449 (3)0.4048 (2)0.7014 (3)0.0978 (8)
O7−0.1209 (3)0.3926 (2)0.80902 (18)0.0821 (6)
O80.1045 (3)0.4242 (3)0.8232 (2)0.1029 (9)
C10.2123 (2)0.2247 (2)0.2352 (2)0.0483 (5)
C20.2772 (2)0.2731 (2)0.3227 (2)0.0463 (4)
C30.1771 (2)0.30467 (19)0.4351 (2)0.0424 (4)
C40.1817 (2)0.3531 (2)0.5561 (2)0.0469 (5)
C50.0511 (3)0.3560 (2)0.6319 (2)0.0483 (5)
C60.0398 (2)0.2773 (2)0.42631 (19)0.0406 (4)
C70.2789 (3)0.1791 (3)0.1093 (2)0.0592 (6)
C80.2451 (5)0.0815 (5)−0.0725 (3)0.0994 (12)
H8A0.35230.0700−0.08540.119*0.368 (18)
H8B0.20090.1469−0.13690.119*0.368 (18)
H8C0.27080.1540−0.12850.119*0.632 (18)
H8D0.33400.0087−0.06670.119*0.632 (18)
C90.208 (3)−0.0509 (13)−0.0829 (17)0.148 (7)0.368 (18)
H9A0.1181−0.0543−0.02860.223*0.368 (18)
H9B0.2880−0.1235−0.05790.223*0.368 (18)
H9C0.1924−0.0595−0.16890.223*0.368 (18)
C9A0.1272 (9)0.0290 (14)−0.1206 (8)0.112 (4)0.632 (18)
H9A10.1651−0.0102−0.20030.168*0.632 (18)
H9A20.04130.1020−0.13160.168*0.632 (18)
H9A30.0998−0.0385−0.06060.168*0.632 (18)
C100.4373 (2)0.2825 (2)0.3058 (3)0.0538 (5)
H10A0.47240.29150.21670.065*
H10B0.44800.35960.34720.065*
C110.6524 (2)0.1574 (2)0.3979 (2)0.0457 (4)
C120.7265 (3)0.0225 (3)0.4536 (3)0.0755 (8)
H12A0.7131−0.04690.40440.113*
H12B0.68300.01100.53910.113*
H12C0.83100.01640.45320.113*
C130.3113 (3)0.3958 (2)0.5957 (3)0.0562 (6)
H13A0.36530.43260.52310.067*
H13B0.27690.46440.65720.067*
C140.5192 (2)0.2971 (2)0.7048 (2)0.0508 (5)
C150.6043 (3)0.1712 (3)0.7674 (3)0.0684 (7)
H15A0.70920.16400.74720.103*
H15B0.57920.09460.73810.103*
H15C0.57960.17360.85750.103*
C160.0166 (4)0.3957 (3)0.7634 (2)0.0638 (6)
C17−0.1557 (5)0.4318 (5)0.9381 (3)0.1211 (17)
H17A−0.14490.52290.94290.145*0.368 (18)
H17B−0.08760.37140.99160.145*0.368 (18)
H17C−0.06210.42050.97360.145*0.632 (18)
H17D−0.20710.52670.93930.145*0.632 (18)
C18−0.3127 (7)0.4253 (12)0.9829 (7)0.097 (3)0.623 (17)
H18A−0.32280.33520.97690.146*0.623 (17)
H18B−0.37960.48710.93110.146*0.623 (17)
H18C−0.33610.44951.06930.146*0.623 (17)
C18A−0.238 (2)0.3432 (15)1.0223 (10)0.107 (5)0.377 (17)
H18D−0.28820.39071.09510.161*0.377 (17)
H18E−0.16800.26251.04910.161*0.377 (17)
H18F−0.30900.31970.97660.161*0.377 (17)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
S10.0368 (2)0.0638 (3)0.0455 (3)−0.0180 (2)−0.00627 (18)−0.0101 (2)
S20.0411 (2)0.0553 (3)0.0445 (3)−0.0177 (2)−0.00618 (19)−0.0085 (2)
O10.0760 (12)0.1018 (15)0.0518 (10)−0.0349 (11)0.0117 (9)−0.0219 (10)
O20.0605 (12)0.1266 (19)0.0884 (15)−0.0303 (12)0.0247 (11)−0.0275 (14)
O30.0380 (7)0.0491 (8)0.0796 (11)−0.0164 (6)−0.0142 (7)0.0062 (7)
O40.0470 (9)0.0678 (11)0.1098 (16)−0.0236 (8)−0.0231 (9)−0.0044 (10)
O50.0529 (8)0.0509 (8)0.0645 (10)−0.0197 (7)−0.0264 (7)0.0003 (7)
O60.0878 (15)0.0713 (13)0.158 (2)−0.0391 (11)−0.0728 (16)0.0083 (14)
O70.1042 (16)0.1005 (15)0.0523 (10)−0.0420 (13)0.0034 (10)−0.0294 (10)
O80.129 (2)0.140 (2)0.0676 (13)−0.0686 (18)−0.0257 (13)−0.0312 (14)
C10.0373 (9)0.0561 (12)0.0520 (11)−0.0139 (8)−0.0019 (8)−0.0022 (9)
C20.0342 (8)0.0440 (10)0.0619 (13)−0.0129 (7)−0.0082 (8)0.0040 (9)
C30.0367 (8)0.0394 (9)0.0552 (11)−0.0144 (7)−0.0140 (8)0.0029 (8)
C40.0493 (10)0.0414 (10)0.0585 (12)−0.0200 (8)−0.0232 (9)0.0021 (8)
C50.0560 (11)0.0487 (11)0.0474 (11)−0.0197 (9)−0.0174 (9)−0.0040 (8)
C60.0351 (8)0.0462 (10)0.0440 (10)−0.0136 (7)−0.0092 (7)−0.0034 (8)
C70.0542 (12)0.0617 (14)0.0585 (14)−0.0143 (11)0.0064 (10)−0.0038 (11)
C80.118 (3)0.129 (3)0.0556 (17)−0.046 (3)0.0230 (18)−0.0279 (19)
C90.175 (18)0.139 (13)0.103 (11)0.008 (13)0.002 (11)−0.009 (10)
C9A0.131 (7)0.137 (8)0.078 (5)−0.048 (6)0.011 (4)−0.048 (5)
C100.0348 (9)0.0542 (12)0.0741 (15)−0.0175 (8)−0.0085 (9)0.0105 (10)
C110.0328 (8)0.0577 (12)0.0477 (11)−0.0132 (8)−0.0030 (7)−0.0046 (9)
C120.0527 (13)0.0770 (18)0.091 (2)−0.0086 (12)−0.0177 (13)0.0174 (15)
C130.0596 (12)0.0508 (12)0.0706 (15)−0.0270 (10)−0.0316 (11)0.0037 (10)
C140.0434 (10)0.0628 (13)0.0514 (12)−0.0186 (9)−0.0118 (8)−0.0057 (10)
C150.0544 (13)0.0790 (17)0.0714 (17)−0.0135 (12)−0.0198 (12)0.0090 (13)
C160.0896 (19)0.0617 (14)0.0500 (13)−0.0309 (13)−0.0161 (12)−0.0082 (11)
C170.176 (5)0.139 (4)0.064 (2)−0.071 (3)0.028 (2)−0.050 (2)
C180.103 (5)0.136 (8)0.059 (4)−0.038 (5)0.005 (3)−0.033 (4)
C18A0.135 (12)0.115 (10)0.071 (6)−0.025 (9)−0.014 (7)−0.018 (6)
Geometric parameters (Å, °) top
S1—C61.705 (2)C9—H9A0.9600
S1—C11.741 (2)C9—H9B0.9600
S2—C61.703 (2)C9—H9C0.9600
S2—C51.736 (2)C9A—H9A10.9600
O1—C71.319 (3)C9A—H9A20.9600
O1—C81.455 (3)C9A—H9A30.9600
O2—C71.200 (3)C10—H10A0.9700
O3—C111.331 (2)C10—H10B0.9700
O3—C101.443 (3)C11—C121.489 (3)
O4—C111.183 (3)C12—H12A0.9600
O5—C141.332 (2)C12—H12B0.9600
O5—C131.444 (3)C12—H12C0.9600
O6—C141.182 (3)C13—H13A0.9700
O7—C161.320 (4)C13—H13B0.9700
O7—C171.443 (4)C14—C151.485 (3)
O8—C161.203 (3)C15—H15A0.9600
C1—C21.362 (3)C15—H15B0.9600
C1—C71.471 (3)C15—H15C0.9600
C2—C31.431 (3)C17—C181.4972 (10)
C2—C101.507 (3)C17—C18A1.4987 (10)
C3—C61.393 (2)C17—H17A0.9700
C3—C41.431 (3)C17—H17B0.9700
C4—C51.369 (3)C17—H17C0.9700
C4—C131.503 (3)C17—H17D0.9700
C5—C161.469 (3)C18—H18A0.9600
C8—C9A1.4988 (10)C18—H18B0.9600
C8—C91.4994 (10)C18—H18C0.9600
C8—H8A0.9700C18A—H18D0.9600
C8—H8B0.9700C18A—H18E0.9600
C8—H8C0.9700C18A—H18F0.9600
C8—H8D0.9700
C6—S1—C190.24 (10)C2—C10—H10A110.7
C6—S2—C589.62 (10)O3—C10—H10B110.7
C7—O1—C8115.4 (2)C2—C10—H10B110.7
C11—O3—C10117.10 (16)H10A—C10—H10B108.8
C14—O5—C13115.27 (17)O4—C11—O3123.4 (2)
C16—O7—C17112.2 (3)O4—C11—C12125.0 (2)
C2—C1—C7127.8 (2)O3—C11—C12111.5 (2)
C2—C1—S1113.60 (17)C11—C12—H12A109.5
C7—C1—S1118.60 (17)C11—C12—H12B109.5
C1—C2—C3111.29 (17)H12A—C12—H12B109.5
C1—C2—C10123.9 (2)C11—C12—H12C109.5
C3—C2—C10124.7 (2)H12A—C12—H12C109.5
C6—C3—C4111.15 (19)H12B—C12—H12C109.5
C6—C3—C2111.75 (18)O5—C13—C4106.55 (16)
C4—C3—C2137.07 (18)O5—C13—H13A110.4
C5—C4—C3110.97 (17)C4—C13—H13A110.4
C5—C4—C13124.0 (2)O5—C13—H13B110.4
C3—C4—C13125.0 (2)C4—C13—H13B110.4
C4—C5—C16126.5 (2)H13A—C13—H13B108.6
C4—C5—S2114.14 (16)O6—C14—O5122.2 (2)
C16—C5—S2119.35 (19)O6—C14—C15125.9 (2)
C3—C6—S2114.09 (15)O5—C14—C15111.9 (2)
C3—C6—S1113.12 (15)C14—C15—H15A109.5
S2—C6—S1132.76 (11)C14—C15—H15B109.5
O2—C7—O1122.8 (3)H15A—C15—H15B109.5
O2—C7—C1125.5 (3)C14—C15—H15C109.5
O1—C7—C1111.7 (2)H15A—C15—H15C109.5
O1—C8—C9A107.7 (3)H15B—C15—H15C109.5
O1—C8—C9108.9 (7)O8—C16—O7124.1 (3)
O1—C8—H8A109.9O8—C16—C5124.0 (3)
C9A—C8—H8A139.2O7—C16—C5111.9 (2)
C9—C8—H8A109.9O7—C17—C18108.9 (3)
O1—C8—H8B109.9O7—C17—C18A113.7 (5)
C9A—C8—H8B72.5O7—C17—H17A109.9
C9—C8—H8B109.9C18—C17—H17A109.9
H8A—C8—H8B108.3C18A—C17—H17A133.7
O1—C8—H8C110.2O7—C17—H17B109.9
C9A—C8—H8C111.5C18—C17—H17B109.9
C9—C8—H8C138.2C18A—C17—H17B70.5
H8A—C8—H8C69.4H17A—C17—H17B108.3
O1—C8—H8D109.8O7—C17—H17C107.6
C9A—C8—H8D109.2C18—C17—H17C138.3
C9—C8—H8D70.6C18A—C17—H17C105.0
H8B—C8—H8D137.3H17A—C17—H17C75.1
H8C—C8—H8D108.5O7—C17—H17D109.6
C8—C9—H9A109.5C18—C17—H17D78.0
H8D—C9—H9A131.3C18A—C17—H17D112.7
C8—C9—H9B109.5H17B—C17—H17D134.0
H8D—C9—H9B72.5H17C—C17—H17D107.8
C8—C9—H9C109.5C17—C18—H18A109.5
H8D—C9—H9C115.5C17—C18—H18B109.5
C8—C9A—H9A1109.5C17—C18—H18C109.5
C8—C9A—H9A2109.5C17—C18A—H18D109.5
H9A1—C9A—H9A2109.5C17—C18A—H18E109.5
C8—C9A—H9A3109.5H18D—C18A—H18E109.5
H9A1—C9A—H9A3109.5C17—C18A—H18F109.5
H9A2—C9A—H9A3109.5H18D—C18A—H18F109.5
O3—C10—C2105.38 (16)H18E—C18A—H18F109.5
O3—C10—H10A110.7
C6—S1—C1—C2−0.51 (18)C1—S1—C6—S2−176.94 (17)
C6—S1—C1—C7178.72 (19)C8—O1—C7—O2−1.0 (5)
C7—C1—C2—C3−178.9 (2)C8—O1—C7—C1−179.6 (3)
S1—C1—C2—C30.2 (2)C2—C1—C7—O2−2.8 (4)
C7—C1—C2—C10−2.9 (4)S1—C1—C7—O2178.1 (2)
S1—C1—C2—C10176.25 (16)C2—C1—C7—O1175.8 (2)
C1—C2—C3—C60.2 (3)S1—C1—C7—O1−3.3 (3)
C10—C2—C3—C6−175.73 (18)C7—O1—C8—C9A179.6 (6)
C1—C2—C3—C4177.8 (2)C7—O1—C8—C9136.4 (11)
C10—C2—C3—C41.9 (4)C11—O3—C10—C2−159.1 (2)
C6—C3—C4—C51.7 (2)C1—C2—C10—O3−92.8 (3)
C2—C3—C4—C5−175.9 (2)C3—C2—C10—O382.6 (3)
C6—C3—C4—C13−178.15 (18)C10—O3—C11—O41.0 (3)
C2—C3—C4—C134.3 (4)C10—O3—C11—C12−178.8 (2)
C3—C4—C5—C16178.0 (2)C14—O5—C13—C4−172.7 (2)
C13—C4—C5—C16−2.2 (4)C5—C4—C13—O591.0 (3)
C3—C4—C5—S2−1.9 (2)C3—C4—C13—O5−89.2 (3)
C13—C4—C5—S2177.97 (16)C13—O5—C14—O6−4.2 (4)
C6—S2—C5—C41.19 (17)C13—O5—C14—C15175.7 (2)
C6—S2—C5—C16−178.7 (2)C17—O7—C16—O82.0 (5)
C4—C3—C6—S2−0.8 (2)C17—O7—C16—C5−179.9 (3)
C2—C3—C6—S2177.42 (14)C4—C5—C16—O8−4.2 (4)
C4—C3—C6—S1−178.87 (14)S2—C5—C16—O8175.6 (2)
C2—C3—C6—S1−0.6 (2)C4—C5—C16—O7177.6 (2)
C5—S2—C6—C3−0.18 (16)S2—C5—C16—O7−2.5 (3)
C5—S2—C6—S1177.39 (17)C16—O7—C17—C18−179.8 (6)
C1—S1—C6—C30.64 (16)C16—O7—C17—C18A−136.2 (10)
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
C10—H10A···O20.972.312.959 (4)123
C13—H13B···O80.972.322.891 (4)117
C17—H17C···O80.972.092.563 (5)108
C10—H10B···O6i0.972.443.243 (3)140
C15—H15C···O2ii0.962.563.453 (4)154
Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) x, y, z+1.
Table 1
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
C10—H10A···O20.972.312.959 (4)123
C13—H13B···O80.972.322.891 (4)117
C17—H17C···O80.972.092.563 (5)108
C10—H10B···O6i0.972.443.243 (3)140
C15—H15C···O2ii0.962.563.453 (4)154
Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) x, y, z+1.
Acknowledgements top

BG thanks the management of AMET University, India, for their kind support. BG also thanks SAIF, IIT, Madras, India, for the data collection.

references
References top

Bernstein, J., Davis, R. E., Shimoni, L. & Chang, N. (1995). Angew. Chem. Int. Ed. Engl. 34, 1555–1573.

Bruker (2004). APEX2. Bruker AXS Inc., Madison, Wisconsin, USA.

Dallemagne, P., Khanh, L. P., Alsaidi, A., Varlet, I., Collot, V., Paillet, M., Bureau, R. & Rault, S. (2003). Bioorg. Chem. 11, 1161–1167.

Dufresne, S. & Skene, W. G. (2008). Acta Cryst. E64, o782.

Graff, J., Harder, S., Wahl, O., Scheuermann, E. H. & Gossmann, J. (2005). Clin. Pharmacol. Ther. 78, 468–476.

Hymete, A., Rohloff, J., Kjosen, H. & Iversen, T. H. (2005). Nat. Prod. Res. 19, 755–761.

Khan, M. S., Ahrens, B., Raithby, P. R. & Teat, S. J. (2004). Acta Cryst. E60, o1226–o1228.

Sheldrick, G. M. (1996). SADABS. University of Göttingen, Germany.

Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122.

Spek, A. L. (2009). Acta Cryst. D65, 148–155.

Tapia, R. A., Alegria, L., Pessoa, C. D., Salas, C., Cortes, M. J., Valderrama, J. A., Sarciron, M. E., Pautet, F., Walchshofer, N. & Fillion, H. (2003). Bioorg. Med. Chem. 11, 2175–2182.