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

Journal logoCRYSTALLOGRAPHIC
COMMUNICATIONS
ISSN: 2056-9890

9β-Hy­dr­oxy-6,9-di­methyl-3-methyl­ene-3a,4,8,9,9a,9b-hexa­hydro­azuleno[4,5-b]furan-2(3H)-one

aLaboratoire de Chimie Biomoléculaire, Substances Naturelles et Réactivité, URAC 16, Faculté des Sciences Semlalia, BP 2390, Bd My Abdellah, 40000 Marrakech, Morocco, bLaboratoire de Chimie de Coordination, 205 route de Narbonne, 31077 Toulouse Cedex 04, France, and cLaboratoire de Chimie Bioorganique et Analytique, URAC 22, BP 146, FSTM, Universite' Hassan II, Mohammedia-Casablanca 20810 Mohammedia, Morocco
*Correspondence e-mail: mberraho@yahoo.fr

(Received 18 December 2011; accepted 3 January 2012; online 14 January 2012)

The title compound, C15H18O3, was synthesized from 9α-hy­droxy­parthenolide (9α-hy­droxy-4,8-dimethyl-12-methylen-3,14-dioxa-tricyclo­[9.3.0.02,4]tetra­dec-7-en-13-one), which was isolated from the chloro­form extract of the aerial parts of Anvillea radiata. The seven-membered ring of the title compound shows a chair conformation, while the five-membered rings exibit different conformations, viz a twisted one for the lactone ring and an envelope conformation for the other five-membered ring with the C atom closest to the hydroxy group forming the flap. In the crystal, O—H⋯O hydrogen bonds connect mol­ecules into dimers that are inter­connected by C—H⋯O inter­actions, producing supramolecular chains along the b axis.

Related literature

For background to the medicinal uses of the plant Anvillea radiata, see: Abdel Sattar et al. (1996[Abdel Sattar, E., Galal, A. M. & Mossa, J. S. (1996). J. Nat. Prod. 59, 403-405.]); Bellakhdar (1997[Bellakhdar, J. (1997). La Pharmacopée Marocaine Traditionnelle, pp. 272-274. Paris: Edition Ibis Press.]); El Hassany et al. (2004[El Hassany, B., El Hanbali, F., Akssira, M., Mellouki, F., Haidou, A. & Barero, A. F. (2004). Fitoterapia, 75, 573-576.]); Qureshi et al. (1990[Qureshi, S., Ageel, A. M., Al-Yahya, M. A., Tariq, M., Mossa, J. S. & Shah, A. H. (1990). J. Ethnopharmacol. 28, 157-162.]). For the reactivity of this sesquiterpene, see: El Haib et al. (2011[El Haib, A., Benharref, A., Sandra, P.-M., Manoury, E., Urrutigoïty, M. & Gouygou, M. (2011). Tetrahedron Asymmetry, 22, 101-108.]) For ring puckering parameters, see: Cremer & Pople (1975[Cremer, D. & Pople, J. A. (1975). J. Am. Chem. Soc. 97, 1354-1358.]).

[Scheme 1]

Experimental

Crystal data
  • C15H18O3

  • Mr = 246.29

  • Monoclinic, C 2

  • a = 15.6732 (9) Å

  • b = 7.4208 (4) Å

  • c = 11.0544 (6) Å

  • β = 103.169 (6)°

  • V = 1251.90 (12) Å3

  • Z = 4

  • Mo Kα radiation

  • μ = 0.09 mm−1

  • T = 180 K

  • 0.42 × 0.19 × 0.12 mm

Data collection
  • Agilent Xcalibur Eos Gemini Ultra diffractometer

  • Absorption correction: multi-scan (CrysAlis PRO; Agilent, 2010[Agilent (2010). CrysAlis PRO. Agilent Technologies Ltd, Yarnton, England.]) Tmin = 0.631, Tmax = 1.000

  • 13492 measured reflections

  • 1378 independent reflections

  • 1313 reflections with I > 2σ(I)

  • Rint = 0.029

Refinement
  • R[F2 > 2σ(F2)] = 0.030

  • wR(F2) = 0.080

  • S = 1.05

  • 1378 reflections

  • 166 parameters

  • 1 restraint

  • H-atom parameters constrained

  • Δρmax = 0.19 e Å−3

  • Δρmin = −0.15 e Å−3

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
O3—H3⋯O2i 0.82 2.31 3.128 (2) 171
C8—H8B⋯O1ii 0.97 2.58 3.500 (2) 158
C7—H7⋯O1iii 0.98 2.65 3.579 (2) 159
Symmetry codes: (i) -x+2, y, -z+2; (ii) [-x+{\script{3\over 2}}, y+{\script{1\over 2}}, -z+2]; (iii) [-x+{\script{3\over 2}}, y-{\script{1\over 2}}, -z+2].

Data collection: CrysAlis PRO (Agilent, 2010[Agilent (2010). CrysAlis PRO. Agilent Technologies Ltd, Yarnton, England.]); cell refinement: CrysAlis PRO; data reduction: CrysAlis PRO; 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: ORTEP-3 for Windows (Farrugia, 1997[Farrugia, L. J. (1997). J. Appl. Cryst. 30, 565.]) and PLATON (Spek, 2009[Spek, A. L. (2009). Acta Cryst. D65, 148-155.]); software used to prepare material for publication: WinGX (Farrugia, 1999[Farrugia, L. J. (1999). J. Appl. Cryst. 32, 837-838.]).

Supporting information


Comment top

Anvillea radiata is a plant that grows in northern Africa and particularly found in the two Maghreb countries, Morocco and Algeria. This plant is used in traditional local medicine for the treatment of dysentery, gastric-intestinal disorders (Bellakhdar, 1997), hypoglycemic activity (Qureshi et al., 1990), and has been reported to have antitumoral activity (Abdel Sattar et al., 1996). In our study of different Moroccan endemic plants, we have demonstrated that the aerial parts of Anvillea radiata could be used as a renewable source of 9-hydroxyparthenolide (El Hassany, et al., 2004). In order to prepare products with high added value that can be used in pharmacology and cosmetics industry, we studied the chemical reactivity of this major constituent of Anvillea radiata. Thus, treatment of this sesquiterpene with Bi(OTf)3 in dichloromethane (El Haib et al., 2011) leads to the litle compound with a yield of 60%. The crystal structure of (I) is reported herein.

The molecule contains three fused rings which exhibit different conformations. The molecular structure of (I), Fig.1, shows the lactone ring to adopt a twisted conformation, as indicated by Cremer & Pople (1975) puckering parameters Q = 0.2747 (18) Å and ϕ = 59.0 (4)° while the other five-membered ring displays an envelope conformation with Q = 0.291 (2)Å and ϕ = 290.3 (4)°. The seven-membered ring has a chair conformation with QT = 0.5793 (16) Å, θ2 = 16.44 (20)°, ϕ2 = -139.46 (75)° and ϕ3 =107.00 (25). In the crystal structure, molecules are connected by O—H···O hydrogen bonds connecting molecules into dimers that again are interconnected by C—H···O interactions to produce infinite chains along b axis (Table 1).

Related literature top

For background to the medicinal uses of the plant Anvillea radiata, see: Abdel Sattar et al. (1996); Bellakhdar (1997); El Hassany et al. (2004); Qureshi et al. (1990). For the reactivity of this sesquiterpene, see: El Haib et al. (2011) For ring puckering parameters, see: Cremer & Pople (1975).

Experimental top

Bi(OTf)3 (39 mg, 6 x 10–2 mmol) was added to a stirred solution of 9β- hydroxyparthenolide (600 mg, 2.27 mmol) in dichloromethane (10 ml). The reaction mixture is left stirring for three hours at room temperature. After completion of the reaction, a saturated solution of NaHCO3 was added and the resulting mixture is extracted three times (3 x 20 mL) with dichloromethane. The organic phases are combined and dried over Na2SO4 and evaporated under vacuum. Chromatography of the residue obtained on a column of silica gel eluting with hexane - ethyl acetate (85/15) allowed the isolation of the title compound (334 mg, 1.35 mmol) with a yield of 60%. Recrystallization from ethyl acetate at room temperature yielded single crystals of the title compound.

Refinement top

All H atoms were fixed geometrically and treated as riding with C—H = 0.96 Å (methyl), 0.97 Å (methylene), 0.98 Å (methine) with Uiso(H) = 1.2Ueq(methylene, methine) or Uiso(H) = 1.5Ueq(methyl, OH). In the absence of significant anomalous scattering, the absolute configuration could not be reliably determined and thus the Friedel pairs were merged and any references to the Flack parameter were removed.

Computing details top

Data collection: CrysAlis PRO (Agilent, 2010); cell refinement: CrysAlis PRO (Agilent, 2010); data reduction: CrysAlis PRO (Agilent, 2010); program(s) used to solve structure: SHELXS97 (Sheldrick,2008); program(s) used to refine structure: SHELXL97 (Sheldrick,2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997) and PLATON (Spek, 2009); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures top
[Figure 1] Fig. 1. : Molecular structure of the title compound with displacement ellipsoids drawn at the 30% probability level. H atoms are represented as small spheres of arbitrary radii.
[Figure 2] Fig. 2. : Partial packing view showing the O–H···O hydrogen bonds as dashed lines. H atoms not involved in hydrogen bonding have been omitted for clarity.
9β-Hydroxy-6,9-dimethyl-3-methylene-3a,4,8,9,9a,9b- hexahydroazuleno[4,5-b]furan-2(3H)-one top
Crystal data top
C15H18O3F(000) = 528
Mr = 246.29Dx = 1.307 Mg m3
Monoclinic, C2Mo Kα radiation, λ = 0.71073 Å
Hall symbol: C 2yCell parameters from 9785 reflections
a = 15.6732 (9) Åθ = 3–26.4°
b = 7.4208 (4) ŵ = 0.09 mm1
c = 11.0544 (6) ÅT = 180 K
β = 103.169 (6)°Box, pale yellow
V = 1251.90 (12) Å30.42 × 0.19 × 0.12 mm
Z = 4
Data collection top
Agilent Xcalibur Eos Gemini Ultra
diffractometer
1378 independent reflections
Radiation source: fine-focus sealed tube1313 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.029
Detector resolution: 8.2632 pixels mm-1θmax = 26.4°, θmin = 3.1°
ω scansh = 1919
Absorption correction: multi-scan
(CrysAlis PRO; Agilent, 2010)
k = 99
Tmin = 0.631, Tmax = 1.000l = 1313
13492 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)] = 0.030Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.080H-atom parameters constrained
S = 1.05 w = 1/[σ2(Fo2) + (0.0581P)2 + 0.1945P]
where P = (Fo2 + 2Fc2)/3
1378 reflections(Δ/σ)max < 0.001
166 parametersΔρmax = 0.19 e Å3
1 restraintΔρmin = 0.15 e Å3
Crystal data top
C15H18O3V = 1251.90 (12) Å3
Mr = 246.29Z = 4
Monoclinic, C2Mo Kα radiation
a = 15.6732 (9) ŵ = 0.09 mm1
b = 7.4208 (4) ÅT = 180 K
c = 11.0544 (6) Å0.42 × 0.19 × 0.12 mm
β = 103.169 (6)°
Data collection top
Agilent Xcalibur Eos Gemini Ultra
diffractometer
1378 independent reflections
Absorption correction: multi-scan
(CrysAlis PRO; Agilent, 2010)
1313 reflections with I > 2σ(I)
Tmin = 0.631, Tmax = 1.000Rint = 0.029
13492 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0301 restraint
wR(F2) = 0.080H-atom parameters constrained
S = 1.05Δρmax = 0.19 e Å3
1378 reflectionsΔρmin = 0.15 e Å3
166 parameters
Special details top

Experimental. Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm. CrysAlisPro (Agilent Technologies, 2010)

Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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
C10.80721 (11)0.4633 (2)0.61618 (14)0.0267 (3)
C20.87339 (12)0.4573 (3)0.55907 (15)0.0380 (4)
H20.86660.47460.47410.046*
C30.95947 (12)0.4201 (4)0.64549 (17)0.0455 (5)
H3A1.00490.49760.62780.055*
H3B0.97660.29530.63990.055*
C40.94229 (10)0.4614 (3)0.77340 (14)0.0322 (4)
C50.84280 (10)0.4259 (2)0.75363 (14)0.0246 (3)
H50.83530.29680.76660.030*
C60.79591 (9)0.5247 (2)0.83742 (14)0.0233 (3)
H60.79500.65400.81920.028*
C70.70300 (10)0.4572 (2)0.82786 (14)0.0265 (3)
H70.70160.32760.81060.032*
C80.63569 (11)0.5483 (3)0.72710 (16)0.0338 (4)
H8A0.57820.50470.73190.041*
H8B0.63720.67660.74430.041*
C90.64585 (11)0.5222 (3)0.59733 (16)0.0323 (4)
H90.59350.53050.53780.039*
C100.71551 (11)0.4891 (2)0.54969 (14)0.0287 (4)
C110.69280 (10)0.4841 (2)0.95746 (15)0.0283 (3)
C120.78211 (11)0.4836 (2)1.03860 (15)0.0290 (3)
C130.62238 (13)0.5135 (3)1.00137 (19)0.0401 (5)
H13A0.62800.53491.08570.048*
H13B0.56720.51290.94790.048*
C140.70133 (13)0.4837 (3)0.41040 (15)0.0402 (4)
H14A0.64030.50110.37340.060*
H14B0.71980.36900.38550.060*
H14C0.73480.57770.38350.060*
C150.96829 (12)0.6516 (3)0.81170 (19)0.0416 (5)
H15A0.95420.67670.89010.062*
H15B0.93710.73350.75010.062*
H15C1.03020.66600.81940.062*
O10.80505 (9)0.4767 (2)1.14968 (11)0.0415 (3)
O20.84070 (7)0.49325 (18)0.96669 (9)0.0290 (3)
O30.98840 (8)0.3361 (2)0.86299 (13)0.0437 (4)
H31.03460.38130.90050.065*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C10.0301 (8)0.0277 (8)0.0211 (7)0.0032 (7)0.0037 (6)0.0003 (7)
C20.0369 (9)0.0543 (12)0.0231 (7)0.0066 (10)0.0078 (7)0.0013 (9)
C30.0317 (9)0.0765 (16)0.0308 (9)0.0111 (10)0.0126 (7)0.0002 (9)
C40.0201 (7)0.0513 (11)0.0253 (7)0.0084 (8)0.0054 (6)0.0037 (8)
C50.0222 (7)0.0281 (8)0.0230 (7)0.0048 (6)0.0039 (5)0.0012 (6)
C60.0211 (7)0.0267 (8)0.0215 (7)0.0020 (6)0.0038 (5)0.0009 (6)
C70.0219 (7)0.0281 (8)0.0299 (8)0.0012 (6)0.0066 (6)0.0011 (7)
C80.0204 (7)0.0410 (10)0.0386 (10)0.0043 (7)0.0037 (7)0.0056 (8)
C90.0241 (8)0.0351 (10)0.0325 (8)0.0005 (7)0.0044 (6)0.0052 (7)
C100.0316 (8)0.0247 (8)0.0258 (7)0.0001 (7)0.0018 (6)0.0015 (7)
C110.0298 (8)0.0238 (8)0.0337 (8)0.0013 (7)0.0122 (6)0.0021 (7)
C120.0336 (8)0.0276 (8)0.0282 (8)0.0031 (8)0.0122 (6)0.0002 (7)
C130.0361 (9)0.0428 (11)0.0471 (10)0.0010 (8)0.0218 (8)0.0011 (9)
C140.0467 (10)0.0422 (11)0.0261 (8)0.0043 (10)0.0030 (7)0.0002 (8)
C150.0245 (8)0.0556 (12)0.0437 (10)0.0066 (8)0.0054 (7)0.0022 (10)
O10.0481 (7)0.0523 (8)0.0255 (6)0.0011 (7)0.0114 (5)0.0005 (6)
O20.0244 (5)0.0407 (7)0.0218 (5)0.0026 (5)0.0049 (4)0.0002 (5)
O30.0232 (6)0.0660 (10)0.0394 (7)0.0125 (6)0.0021 (5)0.0152 (7)
Geometric parameters (Å, º) top
C1—C21.332 (2)C8—C91.492 (3)
C1—C101.470 (2)C8—H8A0.9700
C1—C51.520 (2)C8—H8B0.9700
C2—C31.491 (2)C9—C101.339 (3)
C2—H20.9300C9—H90.9300
C3—C41.530 (2)C10—C141.505 (2)
C3—H3A0.9700C11—C131.321 (2)
C3—H3B0.9700C11—C121.481 (2)
C4—O31.429 (2)C12—O11.199 (2)
C4—C151.503 (3)C12—O21.3464 (19)
C4—C51.547 (2)C13—H13A0.9300
C5—C61.498 (2)C13—H13B0.9300
C5—H50.9800C14—H14A0.9600
C6—O21.4602 (18)C14—H14B0.9600
C6—C71.520 (2)C14—H14C0.9600
C6—H60.9800C15—H15A0.9600
C7—C111.491 (2)C15—H15B0.9600
C7—C81.508 (2)C15—H15C0.9600
C7—H70.9800O3—H30.8200
C2—C1—C10123.05 (14)C9—C8—C7116.23 (15)
C2—C1—C5108.64 (14)C9—C8—H8A108.2
C10—C1—C5128.16 (14)C7—C8—H8A108.2
C1—C2—C3113.02 (14)C9—C8—H8B108.2
C1—C2—H2123.5C7—C8—H8B108.2
C3—C2—H2123.5H8A—C8—H8B107.4
C2—C3—C4103.37 (14)C10—C9—C8132.66 (15)
C2—C3—H3A111.1C10—C9—H9113.7
C4—C3—H3A111.1C8—C9—H9113.7
C2—C3—H3B111.1C9—C10—C1128.26 (14)
C4—C3—H3B111.1C9—C10—C14117.63 (15)
H3A—C3—H3B109.1C1—C10—C14114.06 (15)
O3—C4—C15110.74 (15)C13—C11—C12122.10 (16)
O3—C4—C3110.03 (16)C13—C11—C7131.05 (16)
C15—C4—C3110.80 (17)C12—C11—C7106.76 (13)
O3—C4—C5108.76 (15)O1—C12—O2121.41 (15)
C15—C4—C5113.55 (15)O1—C12—C11129.93 (15)
C3—C4—C5102.67 (13)O2—C12—C11108.66 (13)
C6—C5—C1114.13 (13)C11—C13—H13A120.0
C6—C5—C4116.75 (13)C11—C13—H13B120.0
C1—C5—C4103.81 (12)H13A—C13—H13B120.0
C6—C5—H5107.2C10—C14—H14A109.5
C1—C5—H5107.2C10—C14—H14B109.5
C4—C5—H5107.2H14A—C14—H14B109.5
O2—C6—C5109.43 (12)C10—C14—H14C109.5
O2—C6—C7104.76 (11)H14A—C14—H14C109.5
C5—C6—C7113.14 (13)H14B—C14—H14C109.5
O2—C6—H6109.8C4—C15—H15A109.5
C5—C6—H6109.8C4—C15—H15B109.5
C7—C6—H6109.8H15A—C15—H15B109.5
C11—C7—C8116.08 (14)C4—C15—H15C109.5
C11—C7—C6101.53 (12)H15A—C15—H15C109.5
C8—C7—C6113.67 (14)H15B—C15—H15C109.5
C11—C7—H7108.4C12—O2—C6110.23 (12)
C8—C7—H7108.4C4—O3—H3109.5
C6—C7—H7108.4
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O3—H3···O2i0.822.313.128 (2)171
C8—H8B···O1ii0.972.583.500 (2)158
C7—H7···O1iii0.982.653.579 (2)159
Symmetry codes: (i) x+2, y, z+2; (ii) x+3/2, y+1/2, z+2; (iii) x+3/2, y1/2, z+2.

Experimental details

Crystal data
Chemical formulaC15H18O3
Mr246.29
Crystal system, space groupMonoclinic, C2
Temperature (K)180
a, b, c (Å)15.6732 (9), 7.4208 (4), 11.0544 (6)
β (°) 103.169 (6)
V3)1251.90 (12)
Z4
Radiation typeMo Kα
µ (mm1)0.09
Crystal size (mm)0.42 × 0.19 × 0.12
Data collection
DiffractometerAgilent Xcalibur Eos Gemini Ultra
diffractometer
Absorption correctionMulti-scan
(CrysAlis PRO; Agilent, 2010)
Tmin, Tmax0.631, 1.000
No. of measured, independent and
observed [I > 2σ(I)] reflections
13492, 1378, 1313
Rint0.029
(sin θ/λ)max1)0.625
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.030, 0.080, 1.05
No. of reflections1378
No. of parameters166
No. of restraints1
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.19, 0.15

Computer programs: CrysAlis PRO (Agilent, 2010), SHELXS97 (Sheldrick,2008), SHELXL97 (Sheldrick,2008), ORTEP-3 for Windows (Farrugia, 1997) and PLATON (Spek, 2009), WinGX (Farrugia, 1999).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O3—H3···O2i0.822.313.128 (2)171
C8—H8B···O1ii0.972.583.500 (2)158
C7—H7···O1iii0.982.653.579 (2)159
Symmetry codes: (i) x+2, y, z+2; (ii) x+3/2, y+1/2, z+2; (iii) x+3/2, y1/2, z+2.
 

Acknowledgements

The authors thank Professor El Ammari for useful discussions.

References

First citationAbdel Sattar, E., Galal, A. M. & Mossa, J. S. (1996). J. Nat. Prod. 59, 403–405.  CrossRef CAS PubMed Google Scholar
First citationAgilent (2010). CrysAlis PRO. Agilent Technologies Ltd, Yarnton, England.  Google Scholar
First citationBellakhdar, J. (1997). La Pharmacopée Marocaine Traditionnelle, pp. 272–274. Paris: Edition Ibis Press.  Google Scholar
First citationCremer, D. & Pople, J. A. (1975). J. Am. Chem. Soc. 97, 1354–1358.  CrossRef CAS Web of Science Google Scholar
First citationEl Haib, A., Benharref, A., Sandra, P.-M., Manoury, E., Urrutigoïty, M. & Gouygou, M. (2011). Tetrahedron Asymmetry, 22, 101–108.  Web of Science CrossRef CAS Google Scholar
First citationEl Hassany, B., El Hanbali, F., Akssira, M., Mellouki, F., Haidou, A. & Barero, A. F. (2004). Fitoterapia, 75, 573–576.  Web of Science CrossRef PubMed CAS Google Scholar
First citationFarrugia, L. J. (1997). J. Appl. Cryst. 30, 565.  CrossRef IUCr Journals Google Scholar
First citationFarrugia, L. J. (1999). J. Appl. Cryst. 32, 837–838.  CrossRef CAS IUCr Journals Google Scholar
First citationQureshi, S., Ageel, A. M., Al-Yahya, M. A., Tariq, M., Mossa, J. S. & Shah, A. H. (1990). J. Ethnopharmacol. 28, 157–162.  CrossRef CAS PubMed Web of Science Google Scholar
First citationSheldrick, G. M. (2008). Acta Cryst. A64, 112–122.  Web of Science CrossRef CAS IUCr Journals Google Scholar
First citationSpek, A. L. (2009). Acta Cryst. D65, 148–155.  Web of Science CrossRef CAS IUCr Journals Google Scholar

This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.

Journal logoCRYSTALLOGRAPHIC
COMMUNICATIONS
ISSN: 2056-9890
Follow Acta Cryst. E
Sign up for e-alerts
Follow Acta Cryst. on Twitter
Follow us on facebook
Sign up for RSS feeds