supplementary materials


HTML versionpdf versioncif file3d viewstructure factorssupplementary materialsCIF check reportsimilar papers Open access

Acta Cryst. (2009). E65, o1020-o1021    [ doi:10.1107/S1600536809012525 ]

N-[(3-Phenylsulfanyl-1-phenylsulfonyl-1H-indol-2-yl)methyl]acetamide

S. Thenmozhi, A. SubbiahPandi, V. Dhayalan and A. K. MohanaKrishnan

Abstract top

In the title compound, C23H20N2O3S2, the phenylsulfonyl ring and phenylthio ring make dihedral angles of 66.5 (7) and 81.2 (6)°, respectively, with the indole unit. In the crystal, molecules are linked into centrosymmetric dimers via pairs of N-H...O hydrogen bonds with graph-set motif R22(14). The crystal structure is further stabilized by weak intermolecular C-H...O and very weak C-H...[pi] interactions.

Comment top

Indole derivatives have been found to exhibit antibacterial, antifungal (Singh et al., 2000) and antitumour activities (Andreani et al., 2001). Some of the indole alkaloids extracted from plants possess interesting cytotoxic, antitumour or antiparasitic properties (Quetin-Leclercq, 1994; Mukhopadhyay et al., 1981). Pyrido[1,2-a] indole derivatives have been identified as potent inhibitors of human immunodeficiency virus type 1 (Taylor et al., 1999), and 5-chloro-3-(phenylsulfonyl) indole-2-carboxamide is reported to be a highly potent non-nucleoside inhibitor of HIV-1 reverse transcriptase (Williams et al., 1993). The interaction of phenylsulfonylindole with calf thymus DNA has also been studied by spectroscopic methods (Sivaraman et al., 1996). Against this background, and in order to obtain detailed information on molecular conformations in the solid state, X-ray studies of the title compound (Fig. 1) have been carried out.

The mean plane of the indole ring system makes dihedral angles of 66.5 (7) and 81.2 (6)° with respect to the phenyl rings. The S–O, S–C, and S–N distances are 1.419 (11), 1.750 (13) and 1.679 (11) Å, respectively, these are comparable as observed in similar structures (Ravishankar et al., 2005). As a result of the electron-withdrawing character of the phenylsulfonyl group, the N–Csp2 bond lengths, viz. N1–C1 [1.422 (9) Å] and N1–C8 [1.433 (6) Å], are longer than the mean value of 1.355 (14)Å for N atoms with planar configurations.

Via N2–H2···O2 hydrogen bonds the molecules form cyclic centrosymmetric dimers [R22(14)] shown in Fig.2. The structure is further stabilized by intermolecular C–H···π and C–H···O interactions as shown in Table. 1.

Related literature top

For the biological activity of indole derivatives, see: Singh et al. (2000); Andreani et al. (2001); Quetin-Leclercq (1994); Mukhopadhyay et al. (1981); Taylor et al. (1999); Williams et al. (1993); Sivaraman et al. (1996). For a related structure, see: Ravishankar et al. (2005). Cg2, Cg3 and Cg4 are the centroids of the C1–C6, C12–C17 and C18–C23 rings, respectively.

Experimental top

To a solution of 1-phenylsulfonyl-2-(bromomethyl)-3-(phenylthio)-1H-indole (0.5 g, 1.09 mmol) in dry acetonitrile (20 ml), ZnBr2 (0.49 g, 2.18 mmol), was added. The reaction mixture was then refluxed for 5 hr under N2 atmosphere. It was then poured over ice-water (30 ml) containing 1 ml of conc.HCl, extracted with CHCl3 (30 ml) and dried (Na2 SO4). Removal of solvent followed by crystallization from methanol afforded amide product. The amide was recrystallization from CDCl3. Single crystals of the title compound suitable for X-ray diffraction were obtained by slow evaporation of a solution in methanol.

Refinement top

All H atoms were fixed geometrically and allowed to ride on their parent C atoms, with C–H distances fixed in the range 0.93–0.97 Å with Uiso(H) = 1.5Ueq(C) for methyl H 1.2Ueq(C) for other H atoms.

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: SHELX97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2009).

Figures top
[Figure 1] Fig. 1. View of the title molecule with the atom labeling scheme. The displacement ellipsoids are drawn at the 30% probability level while the H atoms are shown as small spheres of arbitrary radii.
[Figure 2] Fig. 2. The crystal structure showing the centrosymmetric hydrogen bond motif R22(14). For the sake of clarity, the H atoms not involved in the motif have been omitted. The atoms marked with an asterisk (*) are at the symmetry position (-x, 1 - y, 2 - z). The dashed lines indicate the hydrogen bonds.
N-[(3-Phenylsulfanyl-1-phenylsulfonyl-1H-indol-2- yl)methyl]acetamide top
Crystal data top
C23H20N2O3S2Z = 2
Mr = 436.53F(000) = 456
Triclinic, P1Dx = 1.377 Mg m−3
Hall symbol: -P 1Mo Kα radiation, λ = 0.71073 Å
a = 8.8129 (2) ÅCell parameters from 7167 reflections
b = 10.8880 (3) Åθ = 2.4–31.9°
c = 11.3711 (3) ŵ = 0.28 mm−1
α = 86.698 (1)°T = 293 K
β = 76.494 (1)°Block, colourless
γ = 83.317 (1)°0.21 × 0.19 × 0.17 mm
V = 1053.21 (5) Å3
Data collection top
Bruker Kappa APEXII CCD
diffractometer		7167 independent reflections
Radiation source: fine-focus sealed tube5294 reflections with I > 2σ(I)
graphiteRint = 0.026
ω scansθmax = 31.9°, θmin = 2.4°
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)		h = −13→13
Tmin = 0.943, Tmax = 0.953k = −16→16
28160 measured reflectionsl = −16→16
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)] = 0.041Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.121H-atom parameters constrained
S = 0.98 w = 1/[σ2(Fo2) + (0.0595P)2 + 0.2774P]
where P = (Fo2 + 2Fc2)/3
7167 reflections(Δ/σ)max = 0.005
272 parametersΔρmax = 0.33 e Å−3
0 restraintsΔρmin = −0.39 e Å−3
Crystal data top
C23H20N2O3S2γ = 83.317 (1)°
Mr = 436.53V = 1053.21 (5) Å3
Triclinic, P1Z = 2
a = 8.8129 (2) ÅMo Kα radiation
b = 10.8880 (3) ŵ = 0.28 mm−1
c = 11.3711 (3) ÅT = 293 K
α = 86.698 (1)°0.21 × 0.19 × 0.17 mm
β = 76.494 (1)°
Data collection top
Bruker Kappa APEXII CCD
diffractometer		7167 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)		5294 reflections with I > 2σ(I)
Tmin = 0.943, Tmax = 0.953Rint = 0.026
28160 measured reflectionsθmax = 31.9°
Refinement top
R[F2 > 2σ(F2)] = 0.041H-atom parameters constrained
wR(F2) = 0.121Δρmax = 0.33 e Å−3
S = 0.98Δρmin = −0.39 e Å−3
7167 reflectionsAbsolute structure: ?
272 parametersFlack parameter: ?
0 restraintsRogers parameter: ?
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
xyzUiso*/Ueq
C10.80217 (15)0.18662 (12)0.83970 (11)0.0347 (3)
C20.79544 (18)0.07935 (15)0.91125 (14)0.0470 (3)
H20.85320.06440.97030.056*
C30.6993 (2)−0.00414 (16)0.89092 (17)0.0567 (4)
H30.6929−0.07750.93700.068*
C40.6116 (2)0.01768 (16)0.80390 (17)0.0561 (4)
H40.5467−0.04040.79370.067*
C50.61930 (18)0.12411 (15)0.73246 (14)0.0465 (3)
H50.56110.13850.67360.056*
C60.71616 (15)0.20927 (12)0.75069 (11)0.0348 (3)
C70.74318 (15)0.33121 (12)0.69884 (11)0.0338 (3)
C80.83792 (15)0.38163 (12)0.75660 (11)0.0329 (2)
C90.87341 (16)0.51288 (13)0.75136 (13)0.0393 (3)
H9A0.98540.51520.74150.047*
H9B0.84270.55600.68220.047*
C100.64041 (17)0.62259 (15)0.87510 (15)0.0463 (3)
C110.5609 (2)0.66919 (19)0.99829 (18)0.0619 (5)
H11A0.49480.74430.99010.093*
H11B0.63870.68501.04050.093*
H11C0.49820.60811.04300.093*
C121.17375 (14)0.22315 (13)0.72453 (12)0.0355 (3)
C131.23409 (17)0.30613 (15)0.63391 (14)0.0458 (3)
H131.22220.39040.64770.055*
C141.31247 (19)0.26126 (19)0.52229 (16)0.0560 (4)
H141.35370.31570.46010.067*
C151.3295 (2)0.1370 (2)0.50313 (16)0.0602 (5)
H151.38210.10750.42770.072*
C161.2700 (2)0.05551 (18)0.59387 (19)0.0656 (5)
H161.2830−0.02880.57980.079*
C171.19143 (19)0.09758 (15)0.70519 (16)0.0517 (4)
H171.15060.04250.76690.062*
C180.76928 (15)0.32193 (12)0.45609 (11)0.0336 (3)
C190.90885 (16)0.24822 (14)0.45385 (12)0.0417 (3)
H190.94840.23670.52320.050*
C200.98919 (19)0.19193 (16)0.34812 (14)0.0503 (4)
H201.08250.14180.34680.060*
C210.9327 (2)0.20926 (16)0.24488 (14)0.0512 (4)
H210.98820.17190.17380.061*
C220.7938 (2)0.28199 (17)0.24709 (13)0.0524 (4)
H220.75510.29340.17740.063*
C230.71127 (17)0.33808 (15)0.35210 (13)0.0440 (3)
H230.61690.38670.35330.053*
N10.87779 (12)0.29375 (10)0.84621 (9)0.0346 (2)
N20.78974 (13)0.57402 (11)0.86117 (11)0.0403 (3)
H2A0.83710.57920.91850.048*
O11.06998 (14)0.18125 (12)0.95384 (10)0.0559 (3)
O21.09978 (14)0.39630 (11)0.88318 (11)0.0552 (3)
O30.57273 (17)0.62503 (18)0.79379 (14)0.0910 (5)
S11.06294 (4)0.27656 (3)0.86411 (3)0.03906 (10)
S20.65950 (4)0.40353 (3)0.58434 (3)0.04266 (10)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C10.0339 (6)0.0363 (7)0.0294 (6)0.0033 (5)−0.0017 (5)−0.0011 (5)
C20.0472 (8)0.0473 (8)0.0409 (8)0.0023 (6)−0.0049 (6)0.0087 (6)
C30.0589 (10)0.0442 (9)0.0590 (10)−0.0056 (7)−0.0003 (8)0.0117 (7)
C40.0557 (9)0.0456 (9)0.0646 (11)−0.0137 (7)−0.0041 (8)−0.0036 (8)
C50.0465 (8)0.0474 (8)0.0459 (8)−0.0054 (6)−0.0093 (6)−0.0084 (6)
C60.0363 (6)0.0365 (7)0.0288 (6)0.0022 (5)−0.0039 (5)−0.0048 (5)
C70.0373 (6)0.0350 (6)0.0270 (5)0.0056 (5)−0.0072 (5)−0.0034 (5)
C80.0341 (6)0.0346 (6)0.0268 (5)0.0043 (5)−0.0043 (4)−0.0025 (5)
C90.0388 (6)0.0359 (7)0.0403 (7)−0.0002 (5)−0.0049 (5)−0.0030 (5)
C100.0393 (7)0.0476 (8)0.0508 (8)0.0029 (6)−0.0097 (6)−0.0097 (7)
C110.0522 (9)0.0638 (11)0.0635 (11)0.0005 (8)0.0013 (8)−0.0246 (9)
C120.0307 (6)0.0404 (7)0.0362 (6)−0.0001 (5)−0.0105 (5)−0.0041 (5)
C130.0396 (7)0.0441 (8)0.0503 (8)−0.0011 (6)−0.0060 (6)0.0022 (6)
C140.0432 (8)0.0730 (12)0.0446 (8)−0.0027 (7)0.0002 (6)0.0076 (8)
C150.0448 (8)0.0834 (14)0.0490 (9)−0.0026 (8)−0.0006 (7)−0.0234 (9)
C160.0572 (10)0.0559 (11)0.0783 (13)−0.0077 (8)0.0028 (9)−0.0295 (10)
C170.0490 (8)0.0422 (8)0.0576 (9)−0.0052 (6)0.0015 (7)−0.0055 (7)
C180.0365 (6)0.0355 (6)0.0295 (6)−0.0043 (5)−0.0093 (5)0.0010 (5)
C190.0411 (7)0.0508 (8)0.0330 (6)0.0029 (6)−0.0113 (5)−0.0029 (6)
C200.0460 (8)0.0584 (10)0.0411 (8)0.0068 (7)−0.0043 (6)−0.0064 (7)
C210.0606 (9)0.0569 (10)0.0322 (7)−0.0065 (7)−0.0015 (6)−0.0070 (6)
C220.0645 (10)0.0649 (10)0.0310 (7)−0.0076 (8)−0.0170 (7)−0.0010 (7)
C230.0449 (7)0.0534 (9)0.0355 (7)−0.0003 (6)−0.0163 (6)0.0022 (6)
N10.0343 (5)0.0400 (6)0.0282 (5)0.0025 (4)−0.0076 (4)−0.0017 (4)
N20.0391 (6)0.0397 (6)0.0439 (6)0.0019 (5)−0.0137 (5)−0.0120 (5)
O10.0594 (7)0.0743 (8)0.0344 (5)0.0054 (6)−0.0204 (5)0.0089 (5)
O20.0576 (6)0.0579 (7)0.0580 (7)−0.0021 (5)−0.0261 (5)−0.0220 (5)
O30.0563 (8)0.1470 (15)0.0704 (9)0.0362 (9)−0.0318 (7)−0.0335 (9)
S10.04034 (17)0.0485 (2)0.03049 (16)0.00304 (14)−0.01514 (13)−0.00580 (13)
S20.04688 (19)0.0454 (2)0.03417 (17)0.01400 (14)−0.01465 (14)−0.00459 (14)
Geometric parameters (Å, °) top
C1—C21.3834 (19)C12—S11.7496 (13)
C1—C61.3949 (18)C13—C141.382 (2)
C1—N11.4226 (18)C13—H130.9300
C2—C31.376 (2)C14—C151.368 (3)
C2—H20.9300C14—H140.9300
C3—C41.385 (3)C15—C161.370 (3)
C3—H30.9300C15—H150.9300
C4—C51.375 (2)C16—C171.369 (2)
C4—H40.9300C16—H160.9300
C5—C61.386 (2)C17—H170.9300
C5—H50.9300C18—C191.3840 (18)
C6—C71.4439 (19)C18—C231.3885 (17)
C7—C81.3543 (18)C18—S21.7727 (13)
C7—S21.7477 (12)C19—C201.382 (2)
C8—N11.4332 (16)C19—H190.9300
C8—C91.4930 (19)C20—C211.374 (2)
C9—N21.4482 (17)C20—H200.9300
C9—H9A0.9700C21—C221.375 (2)
C9—H9B0.9700C21—H210.9300
C10—O31.2093 (19)C22—C231.379 (2)
C10—N21.3368 (18)C22—H220.9300
C10—C111.500 (2)C23—H230.9300
C11—H11A0.9600N1—S11.6789 (11)
C11—H11B0.9600N2—H2A0.8600
C11—H11C0.9600O1—S11.4193 (11)
C12—C131.382 (2)O2—S11.4198 (12)
C12—C171.382 (2)
C2—C1—C6121.75 (14)C14—C13—H13120.7
C2—C1—N1130.00 (13)C15—C14—C13120.14 (16)
C6—C1—N1108.02 (11)C15—C14—H14119.9
C3—C2—C1116.88 (15)C13—C14—H14119.9
C3—C2—H2121.6C14—C15—C16120.71 (16)
C1—C2—H2121.6C14—C15—H15119.6
C2—C3—C4122.07 (15)C16—C15—H15119.6
C2—C3—H3119.0C17—C16—C15120.32 (17)
C4—C3—H3119.0C17—C16—H16119.8
C5—C4—C3120.89 (16)C15—C16—H16119.8
C5—C4—H4119.6C16—C17—C12119.01 (16)
C3—C4—H4119.6C16—C17—H17120.5
C4—C5—C6118.11 (15)C12—C17—H17120.5
C4—C5—H5120.9C19—C18—C23119.60 (13)
C6—C5—H5120.9C19—C18—S2123.85 (10)
C5—C6—C1120.29 (13)C23—C18—S2116.52 (10)
C5—C6—C7132.35 (13)C20—C19—C18119.66 (13)
C1—C6—C7107.20 (12)C20—C19—H19120.2
C8—C7—C6109.04 (11)C18—C19—H19120.2
C8—C7—S2125.89 (11)C21—C20—C19120.68 (15)
C6—C7—S2125.02 (10)C21—C20—H20119.7
C7—C8—N1108.48 (11)C19—C20—H20119.7
C7—C8—C9128.32 (12)C20—C21—C22119.72 (14)
N1—C8—C9122.13 (11)C20—C21—H21120.1
N2—C9—C8110.29 (11)C22—C21—H21120.1
N2—C9—H9A109.6C21—C22—C23120.40 (14)
C8—C9—H9A109.6C21—C22—H22119.8
N2—C9—H9B109.6C23—C22—H22119.8
C8—C9—H9B109.6C22—C23—C18119.92 (13)
H9A—C9—H9B108.1C22—C23—H23120.0
O3—C10—N2121.55 (15)C18—C23—H23120.0
O3—C10—C11122.30 (15)C1—N1—C8107.23 (10)
N2—C10—C11116.11 (14)C1—N1—S1119.17 (9)
C10—C11—H11A109.5C8—N1—S1118.64 (9)
C10—C11—H11B109.5C10—N2—C9121.31 (12)
H11A—C11—H11B109.5C10—N2—H2A119.3
C10—C11—H11C109.5C9—N2—H2A119.3
H11A—C11—H11C109.5O1—S1—O2119.66 (7)
H11B—C11—H11C109.5O1—S1—N1106.41 (7)
C13—C12—C17121.18 (14)O2—S1—N1106.61 (6)
C13—C12—S1120.19 (11)O1—S1—C12108.97 (7)
C17—C12—S1118.52 (12)O2—S1—C12110.17 (7)
C12—C13—C14118.64 (15)N1—S1—C12103.77 (6)
C12—C13—H13120.7C7—S2—C18101.32 (6)
C6—C1—C2—C3−0.2 (2)C19—C20—C21—C22−0.9 (3)
N1—C1—C2—C3173.51 (14)C20—C21—C22—C230.3 (3)
C1—C2—C3—C4−0.6 (2)C21—C22—C23—C180.5 (2)
C2—C3—C4—C51.0 (3)C19—C18—C23—C22−0.8 (2)
C3—C4—C5—C6−0.5 (2)S2—C18—C23—C22177.16 (12)
C4—C5—C6—C1−0.3 (2)C2—C1—N1—C8−175.59 (13)
C4—C5—C6—C7−175.17 (14)C6—C1—N1—C8−1.19 (13)
C2—C1—C6—C50.7 (2)C2—C1—N1—S146.01 (18)
N1—C1—C6—C5−174.30 (12)C6—C1—N1—S1−139.59 (9)
C2—C1—C6—C7176.72 (12)C7—C8—N1—C10.11 (13)
N1—C1—C6—C71.76 (14)C9—C8—N1—C1169.22 (11)
C5—C6—C7—C8173.66 (14)C7—C8—N1—S1138.76 (10)
C1—C6—C7—C8−1.72 (14)C9—C8—N1—S1−52.12 (14)
C5—C6—C7—S2−3.8 (2)O3—C10—N2—C9−5.2 (3)
C1—C6—C7—S2−179.22 (9)C11—C10—N2—C9172.65 (14)
C6—C7—C8—N10.98 (14)C8—C9—N2—C10−83.42 (16)
S2—C7—C8—N1178.45 (9)C1—N1—S1—O1−43.85 (11)
C6—C7—C8—C9−167.25 (12)C8—N1—S1—O1−177.59 (10)
S2—C7—C8—C910.2 (2)C1—N1—S1—O2−172.62 (10)
C7—C8—C9—N2104.47 (15)C8—N1—S1—O253.64 (11)
N1—C8—C9—N2−62.33 (15)C1—N1—S1—C1271.05 (10)
C17—C12—C13—C140.4 (2)C8—N1—S1—C12−62.69 (11)
S1—C12—C13—C14−175.91 (12)C13—C12—S1—O1−156.18 (11)
C12—C13—C14—C15−0.2 (2)C17—C12—S1—O127.46 (13)
C13—C14—C15—C16−0.2 (3)C13—C12—S1—O2−23.05 (13)
C14—C15—C16—C170.4 (3)C17—C12—S1—O2160.59 (12)
C15—C16—C17—C12−0.2 (3)C13—C12—S1—N190.75 (12)
C13—C12—C17—C16−0.2 (2)C17—C12—S1—N1−85.61 (12)
S1—C12—C17—C16176.18 (14)C8—C7—S2—C18108.39 (12)
C23—C18—C19—C200.2 (2)C6—C7—S2—C18−74.53 (12)
S2—C18—C19—C20−177.54 (12)C19—C18—S2—C7−15.37 (14)
C18—C19—C20—C210.6 (2)C23—C18—S2—C7166.79 (11)
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
N2—H2A···O2i0.862.483.3179 (15)165
C21—H21···O1ii0.932.443.2666 (18)149
C5—H5···Cg3iii0.932.943.7634 (18)149
C9—H9A···Cg4iv0.972.953.5792 (16)124
C11—H11A···Cg2v0.962.913.5974 (21)129
C16—H16···Cg4vi0.932.953.7453 (21)145
Symmetry codes: (i) −x+2, −y+1, −z+2; (ii) x, y, z−1; (iii) x−1, y, z; (iv) −x+2, −y+1, −z+1; (v) −x+1, −y+1, −z+2; (vi) −x+2, −y, −z+1.
Table 1
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
N2—H2A···O2i0.862.483.3179 (15)165
C21—H21···O1ii0.932.443.2666 (18)149
C5—H5···Cg3iii0.932.943.7634 (18)149
C9—H9A···Cg4iv0.972.953.5792 (16)124
C11—H11A···Cg2v0.962.913.5974 (21)129
C16—H16···Cg4vi0.932.953.7453 (21)145
Symmetry codes: (i) −x+2, −y+1, −z+2; (ii) x, y, z−1; (iii) x−1, y, z; (iv) −x+2, −y+1, −z+1; (v) −x+1, −y+1, −z+2; (vi) −x+2, −y, −z+1.
Acknowledgements top

ST and ASP thank Dr J. Jothi Kumar, Principal of Presidency College (Autonomous), Chennai, for providing computer and internet facilities. Dr Babu Vargheese, SAIF, IIT, Madras, India, is thanked for his help with the data collection.

references
References top

Andreani, A., Granaiola, M., Leoni, A., Locatelli, A., Morigi, R., Rambaldi, M., Giorgi, G., Salvini, L. & Garaliene, V. (2001). Anticancer Drug Des. 16, 167–174.

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

Farrugia, L. J. (1997). J. Appl. Cryst. 30, 565.

Mukhopadhyay, S., Handy, G. A., Funayama, S. & Cordell, G. A. (1981). J. Nat. Prod. 44, 696–700.

Quetin-Leclercq, J. (1994). J. Pharm. Belg. 49, 181–192.

Ravishankar, T., Chinnakali, K., Arumugam, N., Srinivasan, P. C., Usman, A. & Fun, H.-K. (2005). Acta Cryst. E61, o2455–o2457.

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

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

Singh, U. P., Sarma, B. K., Mishra, P. K. & Ray, A. B. (2000). Folia Microbiol. 45, 173–176.

Sivaraman, J., Subramanian, K., Velmurugan, D., Subramanian, E. & Seetharaman, J. (1996). J. Mol. Struct. 385, 123–128.

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

Taylor, D. L., Ahmed, P. S., Chambers, P., Tyms, A. S., Bedard, J., Duchaine, J., Falardeau, G., Lavallee, J. F., Brown, W., Rando, R. F. & Bowlin, T. (1999). Antiviral Chem. Chemother. 10, 79–86.

Williams, T. M., Ciccarone, T. M., MacTough, S. C., Rooney, C. S., Balani, S. K., Condra, J. H., Emini, E. A., Goldman, M. E., Greenlee, W. J. & Kauffman, L. R. (1993). J. Med. Chem. 36, 1291–1294.