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

Journal logoCRYSTALLOGRAPHIC
COMMUNICATIONS
ISSN: 2056-9890

5-Hydr­­oxy-7-meth­­oxy-4H-chromen-4-one

aDepartamento de Química, Facultad de Ciencias Básicas, Universidad de Antofagasta, Casilla 170, Antofagasta, Chile, and bInstituto de Bio-Orgánica `Antonio González', Universidad de La Laguna, Astrofísico Francisco Sánchez No. 2, La Laguna, Tenerife, Spain
*Correspondence e-mail: ivanbritob@yahoo.com

(Received 30 November 2007; accepted 11 December 2007; online 18 December 2007)

The mol­ecular conformation of the title compound, C10H8O4, isolated from Laretia acualis, is stabilized by a strong intra­molecular hydrogen bond between the hydroxyl and carbonyl groups. The crystal packing shows ππ stacking inter­actions. The chromene (4H-1-benzopyran-4-one) unit is essentially planar.

Related literature

For related literature, see: Gabor (1988[Gabor, M. (1988). The Pharmacology of Benzopyrone Derivatives and Related Compounds, pp. 91-126. Budapest: Akademiai Kiado.]); Valenti et al. (1993[Valenti, P., Da Re, P., Rampa, A., Montanari, P., Carrara, M. & Cima, L. (1993). Anticancer Drug. Des. 8, 349-360.], 1998[Valenti, P., Bisi, A., Rampa, A., Gobbi, S., Belluti, F., Da Re, P., Cima, L. & Carrara, M. (1998). Anticancer Drug. Des. 13, 881-892.]); Vasconcelos et al. (1998[Vasconcelos, J. M. J., Silva, A. M. S. & Cavaleiro, J. A. S. (1998). Phytochemistry, 49, 1421-1424.]); Bernstein et al. (1995[Bernstein, J., Davis, R. E., Shimoni, L. & Chang, N.-L. (1995). Angew. Chem. Int. Ed. Engl. 34, 1555-1573.]); Wickens (1995[Wickens, G. E. (1995). Econ. Bot. 49, 207-212.]); Wallet & Cody (1995[Wallet, J.-C. & Cody, V. (1995). Acta Cryst. C51, 1193-1195.]).

[Scheme 1]

Experimental

Crystal data
  • C10H8O4

  • Mr = 192.16

  • Monoclinic, P 21 /c

  • a = 9.7551 (3) Å

  • b = 11.7512 (9) Å

  • c = 7.5211 (7) Å

  • β = 95.094 (4)°

  • V = 858.77 (11) Å3

  • Z = 4

  • Mo Kα radiation

  • μ = 0.12 mm−1

  • T = 298 (2) K

  • 0.19 × 0.10 × 0.08 mm

Data collection
  • Nonius KappaCCD area-detector diffractometer

  • Absorption correction: none

  • 1504 measured reflections

  • 1504 independent reflections

  • 1393 reflections with I > 2σ(I)

Refinement
  • R[F2 > 2σ(F2)] = 0.041

  • wR(F2) = 0.115

  • S = 1.08

  • 1504 reflections

  • 131 parameters

  • H atoms treated by a mixture of independent and constrained refinement

  • Δρmax = 0.15 e Å−3

  • Δρmin = −0.17 e Å−3

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
O3—H9⋯O2 0.92 (3) 1.72 (3) 2.5901 (17) 155 (2)

Table 2
ππ interactions (Å,°)

Cg1 and Cg2 are the centroids of rings O1/C2–C4/C4A–C8A and C4A/C5–C8/C8A, respectively. The offset is defined as the distance between CgI and the perpendicular projection of CgJ on ring I.

CgI CgJ CgICgJ Dihedral angle Interplanar distance Offset
Cg1 Cg2i 3.6661 (8) 1.39 3.51 1.13
Cg2 Cg1ii 3.6660 (8) 1.39 3.49 1.06
Cg2 Cg2i 3.7930 (8) 1.69 3.47 1.50
Cg2 Cg2ii 3.7931 (8) 1.69 3.49 1.53
Symmetry codes: (i) [x, {\script{1\over 2}}-y, -{\script{1\over 2}}+z]; (ii) [x, {\script{1\over 2}}-y, {\script{1\over 2}}+z].

Data collection: COLLECT (Nonius, 1998[Nonius (1998). COLLECT. Nonius BV, Delft, The Netherlands.]); cell refinement: DENZO–SMN (Otwinowski & Minor, 1997[Otwinowski, Z. & Minor, W. (1997). Methods in Enzymology, Vol. 276, Macromolecular Crystallography, Part A, edited by C. W. Carter Jr & R. M. Sweet, pp. 307-326. New York; Academic Press.]); data reduction: DENZO–SMN; program(s) used to solve structure: SIR97 (Altomare et al., 1999[Altomare, A., Burla, M. C., Camalli, M., Cascarano, G. L., Giacovazzo, C., Guagliardi, A., Moliterni, A. G. G., Polidori, G. & Spagna, R. (1999). J. Appl. Cryst. 32, 115-119.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997[Sheldrick, G. M. (1997). SHELXL97. University of Göttingen, Germany.]); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997[Farrugia, L. J. (1997). J. Appl. Cryst. 30, 565.]); software used to prepare material for publication: WinGX (Farrugia, 1999[Farrugia, L. J. (1999). J. Appl. Cryst. 32, 837-838.]).

Supporting information


Comment top

The title compound was originally isolated from Artemisia campestris (maritima) (Vasconcelos et al., 1998) and later from Laretia acualis (Cav.) which is known in Chile as "Llareta de la zona central", is a yellowish-green, compact resinous cushion shrub, which grows in the high Andes of Chile. Whole plant infusions are widely used as diabetes treatment in folk medicine (Wickens, 1995). Chromene derivatives exhibits a wide spectrum of biological activity, including spasmolytic, anti-arrhytmic, cardionthonic, antiviral, anticancer and alkylating properties (Gabor, 1988; Valenti et al., 1993, 1998).

The title structure (Fig.1), consists of a chromene moiety substituted in position 5 and 7 with a hydroxy and methoxy group, respectively. The chromene ring system is essentially planar with maximum deviation of -0.007 (2) Å for C2. The geometrical parameters of the chromene group are comparable to those of related structures reported earlier (Wallet & Cody, 1995). The mean bond distances are: O-Csp2 1.3552 (17) Å, and aromatic C—C 1.391 (2) Å, while C4=O2 is 1.2531 (18)Å and C2=C3 is essentially a double bond with a distance of 1.330 (2) Å Å. In the crystal structure, the molecular packing is stabilized by intramolecular O—H···O hydrogen bond generating a graph-set motif S(6) (Bernstein et al., 1995) as well as π- π stacking interactions (Table 2).

Related literature top

For related literature, see: Gabor (1988); Valenti et al. (1993, 1998); Vasconcelos et al. (1998); Bernstein et al. (1995); Wickens (1995); Wallet & Cody (1995).

Experimental top

Dried and finely powdered tissues from the aerial parts of Laretia acualis (535 g) were extracted with petrol ether at room temperature. The solvent was evaporated to dryness by vacuum distillation and low temperature, yielding a gum (15 g). The concentrated petrol ether extract was fractionated on silica gel column with hexane-ethyl acetate mixtures of increasing polarity as elution solvents. The fraction hexane-ethyl acetate 10% (2.45 g) was separated on silica gel using the same elution solvents yielding 45.5 mg of (I)(m.p. 374 K). The title compound was identified by comparing the spectroscopic data with the previously published data (Vasconcelos et al., 1998). Recrystallization from hexane/ethyl acetate (8:2) at room temperature afforded colourless crystals suitable for X-ray diffraction analysis.

Refinement top

H atom attached to O3 atom was located in a difference Fourier map and refined isotropically. All other H atoms were positioned geometrically and then treated as riding, with C—H distances of 0.93 (CH) and 0.96 Å (CH3), and Uiso(H) = 1.2Ueq(C) or Uiso(H) = 1.5Ueq(Cmethyl).

Structure description top

The title compound was originally isolated from Artemisia campestris (maritima) (Vasconcelos et al., 1998) and later from Laretia acualis (Cav.) which is known in Chile as "Llareta de la zona central", is a yellowish-green, compact resinous cushion shrub, which grows in the high Andes of Chile. Whole plant infusions are widely used as diabetes treatment in folk medicine (Wickens, 1995). Chromene derivatives exhibits a wide spectrum of biological activity, including spasmolytic, anti-arrhytmic, cardionthonic, antiviral, anticancer and alkylating properties (Gabor, 1988; Valenti et al., 1993, 1998).

The title structure (Fig.1), consists of a chromene moiety substituted in position 5 and 7 with a hydroxy and methoxy group, respectively. The chromene ring system is essentially planar with maximum deviation of -0.007 (2) Å for C2. The geometrical parameters of the chromene group are comparable to those of related structures reported earlier (Wallet & Cody, 1995). The mean bond distances are: O-Csp2 1.3552 (17) Å, and aromatic C—C 1.391 (2) Å, while C4=O2 is 1.2531 (18)Å and C2=C3 is essentially a double bond with a distance of 1.330 (2) Å Å. In the crystal structure, the molecular packing is stabilized by intramolecular O—H···O hydrogen bond generating a graph-set motif S(6) (Bernstein et al., 1995) as well as π- π stacking interactions (Table 2).

For related literature, see: Gabor (1988); Valenti et al. (1993, 1998); Vasconcelos et al. (1998); Bernstein et al. (1995); Wickens (1995); Wallet & Cody (1995).

Computing details top

Data collection: COLLECT (Nonius, 1998); cell refinement: DENZO–SMN (Otwinowski & Minor, 1997); data reduction: DENZO–SMN (Otwinowski & Minor, 1997); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures top
[Figure 1] Fig. 1. The molecular structure of the title compound, showing the atom-numbering scheme. Displacement ellipsoids are draw at the 30% probability level. The dashed line indicates the intramolecular O–H···O hydrogen bond. H atoms are shown as small spheres of arbitrary radii.
5-Hydroxy-7-methoxy-4H-chromen-4-one top
Crystal data top
C10H8O4F(000) = 400
Mr = 192.16Dx = 1.486 Mg m3
Monoclinic, P21/cMelting point: 374 K
Hall symbol: -P 2ybcMo Kα radiation, λ = 0.71073 Å
a = 9.7551 (3) ÅCell parameters from 1504 reflections
b = 11.7512 (9) Åθ = 3.0–25.0°
c = 7.5211 (7) ŵ = 0.12 mm1
β = 95.094 (4)°T = 298 K
V = 858.77 (11) Å3Prismatic, colourless
Z = 40.19 × 0.10 × 0.08 mm
Data collection top
Nonius KappaCCD area-detector
diffractometer
1393 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0
Graphite monochromatorθmax = 25.3°, θmin = 3.2°
φ scans, and ω scans with κ offsetsh = 1111
1504 measured reflectionsk = 140
1504 independent reflectionsl = 09
Refinement top
Refinement on F20 restraints
Least-squares matrix: fullH atoms treated by a mixture of independent and constrained refinement
R[F2 > 2σ(F2)] = 0.041 w = 1/[σ2(Fo2) + (0.06P)2 + 0.1521P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.115(Δ/σ)max < 0.001
S = 1.08Δρmax = 0.15 e Å3
1504 reflectionsΔρmin = 0.17 e Å3
131 parameters
Crystal data top
C10H8O4V = 858.77 (11) Å3
Mr = 192.16Z = 4
Monoclinic, P21/cMo Kα radiation
a = 9.7551 (3) ŵ = 0.12 mm1
b = 11.7512 (9) ÅT = 298 K
c = 7.5211 (7) Å0.19 × 0.10 × 0.08 mm
β = 95.094 (4)°
Data collection top
Nonius KappaCCD area-detector
diffractometer
1393 reflections with I > 2σ(I)
1504 measured reflectionsRint = 0
1504 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0410 restraints
wR(F2) = 0.115H atoms treated by a mixture of independent and constrained refinement
S = 1.08Δρmax = 0.15 e Å3
1504 reflectionsΔρmin = 0.17 e Å3
131 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
O10.70907 (10)0.05272 (8)0.30079 (14)0.0533 (3)
O20.96609 (11)0.31131 (10)0.18700 (17)0.0649 (4)
O30.77689 (13)0.45485 (9)0.25771 (16)0.0629 (4)
H90.855 (3)0.422 (2)0.219 (3)0.098 (7)*
O40.36201 (10)0.31332 (9)0.43512 (14)0.0558 (3)
C10.27108 (16)0.22189 (16)0.4674 (2)0.0633 (5)
H1A0.18560.25210.50060.095*
H1B0.31210.1750.56220.095*
H1C0.25440.1770.36090.095*
C20.83521 (16)0.03322 (13)0.2464 (2)0.0586 (4)
H20.86260.0420.2350.07*
C30.92292 (15)0.11442 (14)0.2080 (2)0.0568 (4)
H31.00840.09460.17150.068*
C40.88700 (14)0.23206 (12)0.22245 (19)0.0460 (4)
C4A0.75193 (13)0.25315 (10)0.27872 (16)0.0384 (3)
C50.69920 (14)0.36468 (11)0.29717 (17)0.0427 (3)
C60.57034 (15)0.38106 (12)0.35134 (17)0.0460 (4)
H60.53720.45450.36450.055*
C70.48861 (13)0.28748 (12)0.38688 (16)0.0419 (3)
C80.53533 (13)0.17729 (11)0.37016 (17)0.0419 (3)
H80.48080.11520.3940.05*
C8A0.66641 (13)0.16281 (11)0.31662 (17)0.0391 (3)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0439 (6)0.0339 (5)0.0831 (7)0.0016 (4)0.0111 (5)0.0009 (4)
O20.0439 (6)0.0602 (7)0.0922 (8)0.0118 (5)0.0150 (5)0.0044 (6)
O30.0628 (8)0.0378 (6)0.0895 (8)0.0086 (5)0.0146 (6)0.0063 (5)
O40.0431 (6)0.0615 (7)0.0646 (6)0.0096 (5)0.0145 (5)0.0015 (5)
C10.0409 (8)0.0829 (12)0.0677 (10)0.0004 (8)0.0138 (7)0.0061 (8)
C20.0456 (8)0.0432 (8)0.0876 (11)0.0098 (6)0.0105 (7)0.0038 (7)
C30.0376 (8)0.0554 (9)0.0779 (10)0.0068 (7)0.0087 (7)0.0033 (7)
C40.0357 (7)0.0483 (8)0.0536 (8)0.0036 (6)0.0015 (5)0.0015 (6)
C4A0.0353 (7)0.0387 (7)0.0405 (6)0.0017 (5)0.0012 (5)0.0006 (5)
C50.0458 (8)0.0357 (7)0.0458 (7)0.0036 (6)0.0001 (5)0.0023 (5)
C60.0501 (8)0.0372 (7)0.0502 (7)0.0085 (6)0.0026 (6)0.0011 (5)
C70.0376 (7)0.0504 (8)0.0374 (6)0.0040 (6)0.0020 (5)0.0012 (5)
C80.0380 (7)0.0408 (7)0.0470 (7)0.0039 (5)0.0043 (5)0.0015 (5)
C8A0.0377 (7)0.0347 (7)0.0443 (7)0.0007 (5)0.0002 (5)0.0007 (5)
Geometric parameters (Å, º) top
O1—C21.3503 (18)C3—C41.433 (2)
O1—C8A1.3674 (15)C3—H30.93
O2—C41.2531 (17)C4—C4A1.4407 (19)
O3—C51.3510 (16)C4A—C8A1.3952 (18)
O3—H90.92 (2)C4A—C51.4192 (18)
O4—C71.3522 (16)C5—C61.369 (2)
O4—C11.428 (2)C6—C71.398 (2)
C1—H1A0.96C6—H60.93
C1—H1B0.96C7—C81.3821 (19)
C1—H1C0.96C8—C8A1.3848 (18)
C2—C31.330 (2)C8—H80.93
C2—H20.93
C2—O1—C8A118.65 (11)C8A—C4A—C5117.02 (12)
C5—O3—H9103.8 (15)C8A—C4A—C4120.54 (12)
C7—O4—C1118.20 (12)C5—C4A—C4122.44 (12)
O4—C1—H1A109.5O3—C5—C6120.20 (12)
O4—C1—H1B109.5O3—C5—C4A119.18 (13)
H1A—C1—H1B109.5C6—C5—C4A120.62 (12)
O4—C1—H1C109.5C5—C6—C7120.04 (12)
H1A—C1—H1C109.5C5—C6—H6120
H1B—C1—H1C109.5C7—C6—H6120
C3—C2—O1124.40 (14)O4—C7—C8123.45 (13)
C3—C2—H2117.8O4—C7—C6115.13 (12)
O1—C2—H2117.8C8—C7—C6121.42 (12)
C2—C3—C4120.62 (14)C7—C8—C8A117.52 (12)
C2—C3—H3119.7C7—C8—H8121.2
C4—C3—H3119.7C8A—C8—H8121.2
O2—C4—C3122.79 (13)O1—C8A—C8115.95 (11)
O2—C4—C4A122.08 (13)O1—C8A—C4A120.66 (12)
C3—C4—C4A115.12 (12)C8—C8A—C4A123.38 (12)
C8A—O1—C2—C30.7 (2)C1—O4—C7—C81.15 (18)
O1—C2—C3—C40.1 (3)C1—O4—C7—C6177.84 (12)
C2—C3—C4—O2179.70 (15)C5—C6—C7—O4178.42 (11)
C2—C3—C4—C4A0.5 (2)C5—C6—C7—C80.6 (2)
O2—C4—C4A—C8A179.81 (12)O4—C7—C8—C8A178.87 (11)
C3—C4—C4A—C8A0.59 (19)C6—C7—C8—C8A0.05 (19)
O2—C4—C4A—C50.2 (2)C2—O1—C8A—C8179.00 (12)
C3—C4—C4A—C5178.99 (12)C2—O1—C8A—C4A0.52 (19)
C8A—C4A—C5—O3178.38 (11)C7—C8—C8A—O1179.75 (11)
C4—C4A—C5—O31.2 (2)C7—C8—C8A—C4A0.24 (19)
C8A—C4A—C5—C60.52 (19)C5—C4A—C8A—O1179.50 (10)
C4—C4A—C5—C6179.88 (11)C4—C4A—C8A—O10.11 (19)
O3—C5—C6—C7178.07 (11)C5—C4A—C8A—C80.02 (19)
C4A—C5—C6—C70.8 (2)C4—C4A—C8A—C8179.59 (11)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O3—H9···O20.92 (3)1.72 (3)2.5901 (17)155 (2)

Experimental details

Crystal data
Chemical formulaC10H8O4
Mr192.16
Crystal system, space groupMonoclinic, P21/c
Temperature (K)298
a, b, c (Å)9.7551 (3), 11.7512 (9), 7.5211 (7)
β (°) 95.094 (4)
V3)858.77 (11)
Z4
Radiation typeMo Kα
µ (mm1)0.12
Crystal size (mm)0.19 × 0.10 × 0.08
Data collection
DiffractometerNonius KappaCCD area-detector
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
1504, 1504, 1393
Rint0
(sin θ/λ)max1)0.600
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.041, 0.115, 1.08
No. of reflections1504
No. of parameters131
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.15, 0.17

Computer programs: COLLECT (Nonius, 1998), DENZO–SMN (Otwinowski & Minor, 1997), SIR97 (Altomare et al., 1999), SHELXL97 (Sheldrick, 1997), ORTEP-3 for Windows (Farrugia, 1997), WinGX (Farrugia, 1999).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O3—H9···O20.92 (3)1.72 (3)2.5901 (17)155 (2)
ππ interactions (Å,°) top
CgICgJCgI···CgJDihedral angleInterplanar distanceOffset
Cg1Cg2i3.6661 (8)1.393.5081.13
Cg2Cg1ii3.6660 (8)1.393.4871.06
Cg2Cg2i3.7930 (8)1.693.4711.50
Cg2Cg2ii3.7931 (8)1.693.4861.53
Symmetry codes: (i)x, 1/2-y, -1/2+z; (ii) x, 1/2-y, 1/2+z. Cg1 and Cg2 are the centroids of rings O1/C2-C4/C4A–C8A and C4A/C5–C8/C8A, respectively. The offset is defined as the distance between CgI and the perpendicular projection of CgJ on ring I.
 

Acknowledgements

LAL thanks the Fondo Nacional de Desarrollo Científico y Tecnológico de Chile for grant 1060339. We thank the Spanish Research Council (CSIC) for providing us with a free-of-charge licence for the Cambridge Structural Database.

References

First citationAltomare, A., Burla, M. C., Camalli, M., Cascarano, G. L., Giacovazzo, C., Guagliardi, A., Moliterni, A. G. G., Polidori, G. & Spagna, R. (1999). J. Appl. Cryst. 32, 115–119.  Web of Science CrossRef CAS IUCr Journals Google Scholar
First citationBernstein, J., Davis, R. E., Shimoni, L. & Chang, N.-L. (1995). Angew. Chem. Int. Ed. Engl. 34, 1555–1573.  CrossRef CAS Web of Science 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 citationGabor, M. (1988). The Pharmacology of Benzopyrone Derivatives and Related Compounds, pp. 91–126. Budapest: Akademiai Kiado.  Google Scholar
First citationNonius (1998). COLLECT. Nonius BV, Delft, The Netherlands.  Google Scholar
First citationOtwinowski, Z. & Minor, W. (1997). Methods in Enzymology, Vol. 276, Macromolecular Crystallography, Part A, edited by C. W. Carter Jr & R. M. Sweet, pp. 307–326. New York; Academic Press.  Google Scholar
First citationSheldrick, G. M. (1997). SHELXL97. University of Göttingen, Germany.  Google Scholar
First citationValenti, P., Bisi, A., Rampa, A., Gobbi, S., Belluti, F., Da Re, P., Cima, L. & Carrara, M. (1998). Anticancer Drug. Des. 13, 881–892.  Web of Science PubMed CAS Google Scholar
First citationValenti, P., Da Re, P., Rampa, A., Montanari, P., Carrara, M. & Cima, L. (1993). Anticancer Drug. Des. 8, 349–360.  CAS PubMed Web of Science Google Scholar
First citationVasconcelos, J. M. J., Silva, A. M. S. & Cavaleiro, J. A. S. (1998). Phytochemistry, 49, 1421–1424.  Web of Science CrossRef CAS Google Scholar
First citationWallet, J.-C. & Cody, V. (1995). Acta Cryst. C51, 1193–1195.  CSD CrossRef CAS Web of Science IUCr Journals Google Scholar
First citationWickens, G. E. (1995). Econ. Bot. 49, 207–212.  CrossRef 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