organic compounds\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

Journal logoCRYSTALLOGRAPHIC
COMMUNICATIONS
ISSN: 2056-9890

(Z)-5-(3,4,5-Tri­meth­­oxy­styr­yl)-2,3-di­hydro­thieno[3,4-b][1,4]dioxine

aDepartment of Pharmacy, Yantaishan Hospital, Yantai 264000, Shandong, People's Republic of China, and bNanjing Sanhome Pharmaceutical Co. Ltd, Nanjing 210038, Jiangsu, People's Republic of China
*Correspondence e-mail: chugang_1981@163.com

(Received 22 February 2014; accepted 26 February 2014; online 5 March 2014)

In the title compound, C17H18O5S, an analogue of the potent anti­cancer agent combretastatin A-4, the alkene C=C bond has a cis conformation and the C—C=C—C torsion angle is 9.0 (3)°. The dihedral angle between the benzene and thio­phene rings is 54.07 (4)°. The dioxene ring adopts a half-chair conformation, with the C atoms of the methyl­ene groups displaced by −0.325 (2) and 0.341 (3) Å from the plane of the other atoms. The C atoms of the two meta-meth­oxy groups are close to being coplanar with their attached benzene ring [displacements = −0.025 (2) and −0.196 (2) Å], whereas the C atom of the para-meth­oxy group is significantly displaced [by −1.107 (2) Å]. In the crystal, C—H⋯O hydrogen bonds link the mol­ecules into [0-11] chains, which feature two different types of R22(6) loops.

Related literature

For background to combretastatin [systematic name: (Z)-2-meth­oxy-5-(3,4,5-tri­meth­oxy­styr­yl)phenol], see Pettit et al. (1987[Pettit, G. R., Singh, S. B., Niven, M. L., Hamel, E. & Schmidt, J. M. (1987). J. Nat. Prod. 50, 119-131.], 1995[Pettit, G. R., Temple, C. Jr, Narayanan, V. L., Varma, R., Simpson, M. J., Boyd, M. R. & Bansal, N. (1995). Anticancer Drug Res. 10, 299-309.]); Dark et al. (1997[Dark, G. G., Hill, S. A., Prise, V. E., Tozer, G. M., Pettit, G. R. & Chaplin, D. J. (1997). Cancer Res. 57, 1829-1834.]); Thorpe et al. (2003[Thorpe, P. E., Chaplin, D. J. & Blakey, D. C. (2003). Cancer Res. 63, 1144-1147.]); Tozer et al. (2005[Tozer, G. M., Kanthou, C. & Baguley, B. C. (2005). Nat. Rev. Cancer, 5, 423-425.]). For further synthesis details, see Mohannkrishnan et al. (1999[Mohannkrishnan, A. K., Hucke, A., Lyon, M. A., Lakshmikantham, M. V. & Cava, M. P. (1999). Tetrahedron, 55, 11745-11754.]).

[Scheme 1]

Experimental

Crystal data
  • C17H18O5S

  • Mr = 334.37

  • Triclinic, [P \overline 1]

  • a = 8.197 (2) Å

  • b = 8.4527 (15) Å

  • c = 11.835 (3) Å

  • α = 88.774 (1)°

  • β = 85.484 (3)°

  • γ = 76.422 (2)°

  • V = 794.6 (3) Å3

  • Z = 2

  • Mo Kα radiation

  • μ = 0.23 mm−1

  • T = 296 K

  • 0.30 × 0.28 × 0.26 mm

Data collection
  • Bruker SMART CCD diffractometer

  • Absorption correction: multi-scan (SADABS; Bruker, 2008[Bruker (2008). SMART, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.]) Tmin = 0.963, Tmax = 0.985

  • 4342 measured reflections

  • 3059 independent reflections

  • 2766 reflections with I > 2σ(I)

  • Rint = 0.159

Refinement
  • R[F2 > 2σ(F2)] = 0.066

  • wR(F2) = 0.179

  • S = 0.99

  • 3059 reflections

  • 212 parameters

  • H-atom parameters constrained

  • Δρmax = 0.57 e Å−3

  • Δρmin = −0.69 e Å−3

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
C15—H15B⋯O1i 0.96 2.57 3.477 (3) 157
C17—H17B⋯O3ii 0.96 2.57 3.266 (3) 129
Symmetry codes: (i) -x+2, -y+2, -z; (ii) -x+2, -y+1, -z+1.

Data collection: SMART (Bruker, 2008[Bruker (2008). SMART, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.]); cell refinement: SAINT (Bruker, 2008[Bruker (2008). SMART, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.]); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); molecular graphics: SHELXTL (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); software used to prepare material for publication: SHELXL97.

Supporting information


Comment top

Combretastatins are natural products with extraordinary anticancer activity, which were isolated from tree Combretum caffrum (Pettit et al.1987). Among these compounds, combretastatin A-4 ((Z)-2-methoxy-5-(3,4,5-trimethoxystyryl)phenol, CA-4) possesses the most potent antitumor activity as a result of specifically targeting the vasculature of tumors. (Pettit et al. 1995; Dark et al. 1997). Its disodium phosphate prodrug has already developed and entered clinical trials (Thorpe et al.2003; Tozer et al. 2005). Therefore, CA-4 is a very attractive leading compound because of the relatively simple structure and the strong potency against a broad spectrum of human cancer cell lines. The title compound is a new CA-4 analogue, which was prepared by the Wittig reaction (Mohannkrishnan et al. 1999). The antitumor activities of the title compound against HL-60, SMMC-7721 and A549 cancer cell lines in vitro are closely to the natural CA-4. We now report the structure of the title compound (Fig. 1). The C=C bond length is 1.335 (2) Å and two aryl units are on the same sides of the double bond plane. Therefore, it exists as Z configuration. The planes of the two aryl units, benzene ring and thiophene ring, in the molecule make a dihedral angle of 54.07 (4)°. Therefore, the structure of the title compound is very similar as that of the natural combretastatin A-4 (CA-4). In the crystal structure of the title compound, the C—H···O interactions extend the molecules into a zigzag supramolecular array with dangling thiophene rings (Fig. 2).

Related literature top

For background to combretastatin [systematic name: (Z)-2-methoxy-5-(3,4,5-trimethoxystyryl)phenol], see Pettit et al. (1987, 1995); Dark et al. (1997); Thorpe et al. (2003); Tozer et al. (2005). For further synthesis details, see Mohannkrishnan et al. (1999).

Experimental top

To the bromotriphenyl(3,4,5-trimethoxybenzyl)phosphonium salt (5.2 g,10.0 mmol) in dry THF (60 ml) at -78 °C, was added 2.5 Mn-BuLi in hexane (4.0 ml,10.0 mmol) with stirring. After 20 min., a solution of 2,3-dihydrothieno[3,4-b][1,4]dioxine-5-carbaldehyde (1.7 g,10.0 mmol) in dry THF (20 ml) was added and resulting mixture stirred at room temperature for 2 h. Then, the mixture was poured into crushed ice, extracted with ethyl acetate (3*30 ml), dried with MgSO4, and concentrated in vacuo. The resulting solid was purified by column chromatography (petroleum ether/ ethyl acetate, V:V = 5:1) to give white product (1.38 g). Yield: 41.9%. mp. 122–123 °C. The 1H NMR, 13CNMR, MS spectra and elemental analysis are in accord with the assigned structures. Colourless blocks of the title compound were obtained by the slow evaporation of a petroleum ether/ ethyl acetate solution.

Refinement top

(type here to add refinement details)

Computing details top

Data collection: SMART (Bruker, 2008); cell refinement: SAINT (Bruker, 2008); data reduction: SAINT (Bruker, 2008); 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: SHELXL97 (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. View of the title compound, showing 50% probability ellipsoids.
[Figure 2] Fig. 2. A hydrogen-bonded chain in the title compound.
(Z)-5-(3,4,5-Trimethoxystyryl)-2,3-dihydrothieno[3,4-b][1,4]dioxine top
Crystal data top
C17H18O5SZ = 2
Mr = 334.37F(000) = 352
Triclinic, P1Dx = 1.397 Mg m3
Hall symbol: -P 1Mo Kα radiation, λ = 0.71073 Å
a = 8.197 (2) ÅCell parameters from 3471 reflections
b = 8.4527 (15) Åθ = 2.5–28.3°
c = 11.835 (3) ŵ = 0.23 mm1
α = 88.774 (1)°T = 296 K
β = 85.484 (3)°Block, colorless
γ = 76.422 (2)°0.30 × 0.28 × 0.26 mm
V = 794.6 (3) Å3
Data collection top
Bruker SMART CCD
diffractometer
3059 independent reflections
Radiation source: fine-focus sealed tube2766 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.159
ω scansθmax = 26.0°, θmin = 2.5°
Absorption correction: multi-scan
(SADABS; Bruker, 2008)
h = 105
Tmin = 0.963, Tmax = 0.985k = 1010
4342 measured reflectionsl = 1414
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.066H-atom parameters constrained
wR(F2) = 0.179 w = 1/[σ2(Fo2) + (0.1373P)2 + 0.0901P]
where P = (Fo2 + 2Fc2)/3
S = 0.99(Δ/σ)max < 0.001
3059 reflectionsΔρmax = 0.57 e Å3
212 parametersΔρmin = 0.69 e Å3
0 restraintsExtinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.75 (5)
Crystal data top
C17H18O5Sγ = 76.422 (2)°
Mr = 334.37V = 794.6 (3) Å3
Triclinic, P1Z = 2
a = 8.197 (2) ÅMo Kα radiation
b = 8.4527 (15) ŵ = 0.23 mm1
c = 11.835 (3) ÅT = 296 K
α = 88.774 (1)°0.30 × 0.28 × 0.26 mm
β = 85.484 (3)°
Data collection top
Bruker SMART CCD
diffractometer
3059 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2008)
2766 reflections with I > 2σ(I)
Tmin = 0.963, Tmax = 0.985Rint = 0.159
4342 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0660 restraints
wR(F2) = 0.179H-atom parameters constrained
S = 0.99Δρmax = 0.57 e Å3
3059 reflectionsΔρmin = 0.69 e Å3
212 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
xyzUiso*/Ueq
C10.7976 (2)0.5843 (2)0.05341 (13)0.0332 (4)
H10.77500.60540.02190.040*
C20.8766 (2)0.6846 (2)0.10955 (14)0.0341 (4)
C30.9126 (2)0.6527 (2)0.22295 (14)0.0346 (4)
C40.8656 (2)0.5213 (2)0.27815 (13)0.0339 (4)
C50.7875 (2)0.4201 (2)0.22159 (13)0.0339 (4)
H50.75910.33110.25880.041*
C60.75215 (19)0.4526 (2)0.10883 (13)0.0319 (4)
C70.6789 (2)0.3434 (2)0.04398 (13)0.0358 (4)
H70.70740.34180.03370.043*
C80.5779 (2)0.2464 (2)0.07919 (14)0.0362 (4)
H80.56060.17610.02430.043*
C90.4900 (2)0.2326 (2)0.19020 (14)0.0354 (4)
C100.3068 (3)0.2738 (3)0.37088 (18)0.0544 (6)
H100.23950.31150.43620.065*
C110.3539 (2)0.1146 (3)0.33906 (15)0.0439 (5)
C120.4559 (2)0.0932 (2)0.23456 (13)0.0340 (4)
C130.4314 (3)0.1752 (2)0.23211 (18)0.0548 (6)
H13A0.49550.28260.20880.066*
H13B0.32060.15850.20400.066*
C140.4144 (4)0.1663 (3)0.3584 (2)0.0671 (7)
H14A0.36530.25360.38880.081*
H14B0.52500.18090.38650.081*
C150.8706 (3)0.8662 (2)0.04727 (16)0.0465 (5)
H15A0.91720.78180.10160.070*
H15B0.90680.96310.06970.070*
H15C0.75000.88830.04370.070*
C160.9071 (3)0.9017 (3)0.3128 (2)0.0597 (6)
H16A0.85080.95740.25020.090*
H16B0.98180.96290.33870.090*
H16C0.82530.89090.37340.090*
C170.8570 (3)0.3659 (3)0.44741 (16)0.0570 (6)
H17A0.73780.37710.44700.085*
H17B0.88730.36370.52430.085*
H17C0.91520.26640.41030.085*
O10.92692 (17)0.81485 (16)0.06163 (10)0.0434 (4)
O21.00158 (17)0.74368 (16)0.27742 (11)0.0449 (4)
O30.90251 (18)0.49911 (17)0.38942 (10)0.0426 (4)
O40.3099 (2)0.0118 (2)0.39693 (13)0.0637 (5)
O50.51392 (17)0.05526 (15)0.18353 (10)0.0418 (4)
S10.38731 (7)0.39573 (6)0.27505 (5)0.0536 (3)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C10.0339 (8)0.0410 (9)0.0268 (7)0.0138 (7)0.0016 (6)0.0030 (6)
C20.0317 (8)0.0386 (9)0.0341 (8)0.0145 (7)0.0038 (6)0.0020 (7)
C30.0356 (8)0.0388 (9)0.0329 (8)0.0154 (7)0.0012 (6)0.0075 (7)
C40.0352 (8)0.0407 (9)0.0268 (8)0.0111 (7)0.0003 (6)0.0067 (6)
C50.0393 (9)0.0349 (8)0.0301 (8)0.0149 (7)0.0010 (6)0.0021 (6)
C60.0315 (8)0.0367 (8)0.0289 (7)0.0119 (6)0.0029 (6)0.0069 (6)
C70.0449 (9)0.0405 (9)0.0253 (7)0.0174 (7)0.0006 (6)0.0057 (6)
C80.0430 (9)0.0380 (9)0.0314 (8)0.0172 (7)0.0007 (6)0.0084 (6)
C90.0344 (8)0.0391 (9)0.0347 (8)0.0130 (7)0.0016 (6)0.0094 (7)
C100.0538 (11)0.0611 (13)0.0480 (11)0.0191 (10)0.0214 (9)0.0226 (9)
C110.0442 (10)0.0529 (11)0.0366 (9)0.0185 (8)0.0090 (7)0.0094 (8)
C120.0341 (8)0.0391 (9)0.0300 (8)0.0121 (7)0.0030 (6)0.0093 (6)
C130.0737 (14)0.0382 (10)0.0539 (12)0.0231 (10)0.0185 (10)0.0036 (8)
C140.0922 (18)0.0546 (13)0.0543 (13)0.0253 (13)0.0184 (12)0.0081 (10)
C150.0553 (11)0.0502 (11)0.0403 (9)0.0253 (9)0.0041 (8)0.0072 (8)
C160.0674 (14)0.0547 (12)0.0625 (13)0.0240 (11)0.0031 (10)0.0239 (10)
C170.0788 (15)0.0702 (14)0.0343 (9)0.0404 (12)0.0135 (9)0.0104 (9)
O10.0514 (8)0.0488 (8)0.0388 (7)0.0296 (6)0.0044 (5)0.0062 (6)
O20.0485 (8)0.0448 (8)0.0480 (7)0.0216 (6)0.0104 (6)0.0074 (6)
O30.0574 (8)0.0486 (7)0.0284 (6)0.0242 (6)0.0078 (5)0.0003 (5)
O40.0793 (11)0.0662 (10)0.0479 (8)0.0317 (9)0.0283 (7)0.0076 (7)
O50.0534 (8)0.0344 (7)0.0382 (7)0.0164 (6)0.0142 (5)0.0073 (5)
S10.0570 (4)0.0406 (4)0.0624 (4)0.0154 (3)0.0180 (3)0.0209 (2)
Geometric parameters (Å, º) top
C1—C21.389 (2)C11—C121.427 (2)
C1—C61.391 (2)C12—O51.368 (2)
C1—H10.9300C13—O51.432 (2)
C2—O11.3611 (19)C13—C141.492 (3)
C2—C31.404 (2)C13—H13A0.9700
C3—O21.3778 (18)C13—H13B0.9700
C3—C41.392 (2)C14—O41.444 (3)
C4—O31.3734 (19)C14—H14A0.9700
C4—C51.393 (2)C14—H14B0.9700
C5—C61.396 (2)C15—O11.428 (2)
C5—H50.9300C15—H15A0.9600
C6—C71.471 (2)C15—H15B0.9600
C7—C81.335 (2)C15—H15C0.9600
C7—H70.9300C16—O21.431 (3)
C8—C91.464 (2)C16—H16A0.9600
C8—H80.9300C16—H16B0.9600
C9—C121.359 (2)C16—H16C0.9600
C9—S11.7322 (17)C17—O31.415 (2)
C10—C111.363 (3)C17—H17A0.9600
C10—S11.713 (2)C17—H17B0.9600
C10—H100.9300C17—H17C0.9600
C11—O41.360 (2)
C2—C1—C6120.60 (14)O5—C13—C14111.46 (17)
C2—C1—H1119.7O5—C13—H13A109.3
C6—C1—H1119.7C14—C13—H13A109.3
O1—C2—C1124.50 (15)O5—C13—H13B109.3
O1—C2—C3115.47 (14)C14—C13—H13B109.3
C1—C2—C3120.02 (15)H13A—C13—H13B108.0
O2—C3—C4120.04 (14)O4—C14—C13111.1 (2)
O2—C3—C2120.78 (15)O4—C14—H14A109.4
C4—C3—C2119.08 (14)C13—C14—H14A109.4
O3—C4—C3115.81 (14)O4—C14—H14B109.4
O3—C4—C5123.31 (15)C13—C14—H14B109.4
C3—C4—C5120.88 (14)H14A—C14—H14B108.0
C4—C5—C6119.71 (15)O1—C15—H15A109.5
C4—C5—H5120.1O1—C15—H15B109.5
C6—C5—H5120.1H15A—C15—H15B109.5
C1—C6—C5119.70 (14)O1—C15—H15C109.5
C1—C6—C7118.70 (14)H15A—C15—H15C109.5
C5—C6—C7121.44 (14)H15B—C15—H15C109.5
C8—C7—C6130.10 (14)O2—C16—H16A109.5
C8—C7—H7115.0O2—C16—H16B109.5
C6—C7—H7115.0H16A—C16—H16B109.5
C7—C8—C9130.45 (14)O2—C16—H16C109.5
C7—C8—H8114.8H16A—C16—H16C109.5
C9—C8—H8114.8H16B—C16—H16C109.5
C12—C9—C8125.05 (15)O3—C17—H17A109.5
C12—C9—S1109.52 (12)O3—C17—H17B109.5
C8—C9—S1124.81 (13)H17A—C17—H17B109.5
C11—C10—S1111.34 (14)O3—C17—H17C109.5
C11—C10—H10124.3H17A—C17—H17C109.5
S1—C10—H10124.3H17B—C17—H17C109.5
O4—C11—C10125.54 (17)C2—O1—C15117.07 (13)
O4—C11—C12122.54 (17)C3—O2—C16114.95 (14)
C10—C11—C12111.91 (18)C4—O3—C17117.00 (13)
C9—C12—O5123.02 (14)C11—O4—C14111.51 (15)
C9—C12—C11114.32 (16)C12—O5—C13112.21 (13)
O5—C12—C11122.66 (16)C10—S1—C992.85 (9)
C6—C1—C2—O1179.31 (15)S1—C9—C12—O5177.21 (13)
C6—C1—C2—C30.5 (2)C8—C9—C12—C11173.91 (17)
O1—C2—C3—O23.6 (2)S1—C9—C12—C112.66 (19)
C1—C2—C3—O2175.28 (15)O4—C11—C12—C9178.64 (16)
O1—C2—C3—C4179.85 (14)C10—C11—C12—C92.1 (2)
C1—C2—C3—C41.0 (3)O4—C11—C12—O51.5 (3)
O2—C3—C4—O34.7 (2)C10—C11—C12—O5177.77 (17)
C2—C3—C4—O3179.03 (15)O5—C13—C14—O463.0 (3)
O2—C3—C4—C5174.82 (15)C1—C2—O1—C1510.4 (3)
C2—C3—C4—C51.5 (3)C3—C2—O1—C15170.77 (16)
O3—C4—C5—C6179.03 (15)C4—C3—O2—C16106.9 (2)
C3—C4—C5—C61.5 (3)C2—C3—O2—C1676.9 (2)
C2—C1—C6—C50.6 (2)C3—C4—O3—C17179.64 (17)
C2—C1—C6—C7176.03 (15)C5—C4—O3—C170.2 (3)
C4—C5—C6—C11.0 (2)C10—C11—O4—C14164.6 (2)
C4—C5—C6—C7176.38 (15)C12—C11—O4—C1416.3 (3)
C1—C6—C7—C8155.46 (19)C13—C14—O4—C1146.7 (3)
C5—C6—C7—C829.2 (3)C9—C12—O5—C13166.87 (17)
C6—C7—C8—C99.0 (3)C11—C12—O5—C1313.0 (2)
C7—C8—C9—C12148.21 (19)C14—C13—O5—C1243.6 (2)
C7—C8—C9—S141.8 (3)C11—C10—S1—C90.85 (18)
S1—C10—C11—O4179.73 (16)C12—C9—S1—C102.00 (14)
S1—C10—C11—C120.5 (2)C8—C9—S1—C10173.28 (16)
C8—C9—C12—O55.9 (3)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C15—H15B···O1i0.962.573.477 (3)157
C17—H17B···O3ii0.962.573.266 (3)129
Symmetry codes: (i) x+2, y+2, z; (ii) x+2, y+1, z+1.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C15—H15B···O1i0.962.573.477 (3)157
C17—H17B···O3ii0.962.573.266 (3)129
Symmetry codes: (i) x+2, y+2, z; (ii) x+2, y+1, z+1.
 

References

First citationBruker (2008). SMART, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.  Google Scholar
First citationDark, G. G., Hill, S. A., Prise, V. E., Tozer, G. M., Pettit, G. R. & Chaplin, D. J. (1997). Cancer Res. 57, 1829–1834.  CAS PubMed Web of Science Google Scholar
First citationMohannkrishnan, A. K., Hucke, A., Lyon, M. A., Lakshmikantham, M. V. & Cava, M. P. (1999). Tetrahedron, 55, 11745–11754.  Google Scholar
First citationPettit, G. R., Singh, S. B., Niven, M. L., Hamel, E. & Schmidt, J. M. (1987). J. Nat. Prod. 50, 119–131.  CSD CrossRef CAS PubMed Web of Science Google Scholar
First citationPettit, G. R., Temple, C. Jr, Narayanan, V. L., Varma, R., Simpson, M. J., Boyd, M. R. & Bansal, N. (1995). Anticancer Drug Res. 10, 299–309.  CAS Google Scholar
First citationSheldrick, G. M. (2008). Acta Cryst. A64, 112–122.  Web of Science CrossRef CAS IUCr Journals Google Scholar
First citationThorpe, P. E., Chaplin, D. J. & Blakey, D. C. (2003). Cancer Res. 63, 1144–1147.  PubMed CAS Google Scholar
First citationTozer, G. M., Kanthou, C. & Baguley, B. C. (2005). Nat. Rev. Cancer, 5, 423–425.  Web of Science CrossRef PubMed CAS Google Scholar

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