PMCCPMCCPMCC

Search tips
Search criteria 

Advanced

 
Logo of actaeInternational Union of Crystallographysearchopen accessarticle submissionjournal home pagethis article
 
Acta Crystallogr Sect E Struct Rep Online. 2009 December 1; 65(Pt 12): o3144–o3145.
Published online 2009 November 21. doi:  10.1107/S1600536809048934
PMCID: PMC2971847

3-Acetyl-6-chloro-2-methyl-4-phenyl­quinolinium hydrogen sulfate

Abstract

In the title salt, C18H15ClNO+·HSO4 , the quinolinium ring system is approximately planar, with a maximum deviation of 0.028 (2) Å, and forms a dihedral angle of 78.43 (4)° with the attached phenyl ring. A pair of inter­molecular O—H(...)O hydrogen bonds links two hydrogen sulfate anions into a dimer, generating a R 2 2(8) ring motif. Inter­molecular N—H(...)O hydrogen bonds and C—H(...)O contacts link the ions into a three-dimensional network. The structure is further stabilized by C—H(...)π inter­actions

Related literature

For the background to and biological activities of quinolines, see: Morimoto et al. (1991 [triangle]); Michael (1997 [triangle]); Markees et al. (1970 [triangle]); Campbell et al. (1988 [triangle]); Maguire et al. (1994 [triangle]); Kalluraya & Sreenivasa (1998 [triangle]); Roma et al. (2000 [triangle]); Chen et al. (2001 [triangle]). For related structure: see: Fun et al. (2009 [triangle]). For hydrogen bond motifs, see: Bernstein et al. (1995 [triangle]). For the stability of the temperature controller used for the data collection, see: Cosier & Glazer (1986 [triangle]).

An external file that holds a picture, illustration, etc.
Object name is e-65-o3144-scheme1.jpg

Experimental

Crystal data

  • C18H15ClNO+·HSO4
  • M r = 393.83
  • Triclinic, An external file that holds a picture, illustration, etc.
Object name is e-65-o3144-efi1.jpg
  • a = 7.3912 (1) Å
  • b = 8.8547 (1) Å
  • c = 13.3413 (2) Å
  • α = 92.485 (1)°
  • β = 91.889 (1)°
  • γ = 99.539 (1)°
  • V = 859.55 (2) Å3
  • Z = 2
  • Mo Kα radiation
  • μ = 0.37 mm−1
  • T = 100 K
  • 0.28 × 0.18 × 0.11 mm

Data collection

  • Bruker SMART APEXII CCD area-detector diffractometer
  • Absorption correction: multi-scan (SADABS; Bruker, 2005 [triangle]) T min = 0.902, T max = 0.960
  • 20789 measured reflections
  • 5036 independent reflections
  • 4099 reflections with I > 2σ(I)
  • R int = 0.036

Refinement

  • R[F 2 > 2σ(F 2)] = 0.044
  • wR(F 2) = 0.100
  • S = 1.05
  • 5036 reflections
  • 299 parameters
  • All H-atom parameters refined
  • Δρmax = 0.49 e Å−3
  • Δρmin = −0.46 e Å−3

Data collection: APEX2 (Bruker, 2005 [triangle]); cell refinement: SAINT (Bruker, 2005 [triangle]); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008 [triangle]); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009 [triangle]).

Table 1
Hydrogen-bond geometry (Å, °)

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536809048934/tk2576sup1.cif

Structure factors: contains datablocks I. DOI: 10.1107/S1600536809048934/tk2576Isup2.hkl

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Acknowledgments

HKF and WSL thank USM for the Research University Golden Goose Grant (1001/PFIZIK/811012). WSL thanks the Malaysian government and USM for the award of the post of Assistant Research Officer under the Research University Golden Goose Grant (1001/PFIZIK/811012). VV is grateful to DST-India for funding through the Young Scientist Scheme (Fast Track Proposal).

supplementary crystallographic information

Comment

Quinolines and their derivatives are very important compounds because of their wide occurrence in natural products (Morimoto et al., 1991; Michael, 1997) and biologically active compounds (Markees et al., 1970; Campbell et al., 1988). A large variety of quinolines have interesting physiological activities and have found attractive applications as pharmaceuticals, agrochemicals and as synthetic building blocks (Maguire et al., 1994; Kalluraya & Sreenivasa, 1998; Roma et al., 2000; Chen et al., 2001). The 3-acetyl-6-chloro-2-methyl-4-phenylquinoline has been synthesized using the method available in the literature (Fun et al., 2009), and then converted into the title salt, (I).

The asymmetric unit of (I), Fig. 1, contains a 3-acetyl-6-chloro-2-methyl-4-phenylquinolinium cation and a hydrogen sulfate anion. One proton is transferred from the hydroxyl group of hydrogen sulfate to the atom N1 of 3-acetyl-6-chloro-2-methyl-4-phenylquinoline during crystallisation resulting in the formation of salt, (I). The quinolinium ring system (C1–C9/N1) is approximately planar with a maximum deviation of 0.028 (2) Å at atom C7. This mean plane of the quinolinium ring forms a dihedral angle of 78.43 (4)° with the phenyl ring (C10–C15). Bond lengths and angles are comparable to a closely related structure (Fun et al., 2009).

In the crystal packing (Fig. 2), a pair of O2—H1O2···O3 hydrogen bonds link two hydrogen sulfate anions into dimers, generating R22(8) ring motifs stacked along a axis (Bernstein et al., 1995). A N1—H1N1—O5 hydrogen bond links the dimer with the quinolinium ring system. The ions are linked into a 3-D network by C5—H5A···O3, C15—H15A···O4 and C16—H16C···O4 contacts. The structure is further stabilized by C—H···π interactions (Table 1), involving C1–C6 (centroid Cg1) ring system.

Experimental

To a solution of 3-acetyl-6-chloro-2-methyl-4-phenylquinoline (10 ml, 1 M) in ethanol, copper sulfate solution (1 ml, 1 M) and concentrated H2SO4 (1 ml) was added and then refluxed for about 10 min. The contents were filtered and kept for 92 h for crystallization.

Refinement

All hydrogen atoms were located from the difference Fourier map and were refined freely (range of C–H = 0.91 (3) - 0.96 (3) Å and see Table 1).

Figures

Fig. 1.
The molecular structure of (I), showing 30% probability displacement ellipsoids and the atom-numbering scheme.
Fig. 2.
The crystal packing of (I), viewed along the a axis, showing the 3-D network. H atoms not involved in the intermolecular interactions (dashed lines) have been omitted for clarity.

Crystal data

C18H15ClNO+·HSO4Z = 2
Mr = 393.83F(000) = 408
Triclinic, P1Dx = 1.522 Mg m3
Hall symbol: -P 1Mo Kα radiation, λ = 0.71073 Å
a = 7.3912 (1) ÅCell parameters from 6943 reflections
b = 8.8547 (1) Åθ = 2.3–30.0°
c = 13.3413 (2) ŵ = 0.37 mm1
α = 92.485 (1)°T = 100 K
β = 91.889 (1)°Block, colourless
γ = 99.539 (1)°0.28 × 0.18 × 0.11 mm
V = 859.55 (2) Å3

Data collection

Bruker SMART APEXII CCD area-detector diffractometer5036 independent reflections
Radiation source: fine-focus sealed tube4099 reflections with I > 2σ(I)
graphiteRint = 0.036
[var phi] and ω scansθmax = 30.1°, θmin = 2.3°
Absorption correction: multi-scan (SADABS; Bruker, 2005)h = −10→10
Tmin = 0.902, Tmax = 0.960k = −12→12
20789 measured reflectionsl = −17→18

Refinement

Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.044Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.100All H-atom parameters refined
S = 1.05w = 1/[σ2(Fo2) + (0.0423P)2 + 0.5203P] where P = (Fo2 + 2Fc2)/3
5036 reflections(Δ/σ)max < 0.001
299 parametersΔρmax = 0.49 e Å3
0 restraintsΔρmin = −0.46 e Å3

Special details

Experimental. The crystal was placed in the cold stream of an Oxford Cyrosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.
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)

xyzUiso*/Ueq
Cl1−0.07965 (6)1.15710 (5)0.87223 (3)0.02195 (11)
O10.84858 (17)0.74796 (14)0.81500 (10)0.0227 (3)
N10.56245 (19)1.06536 (16)0.64462 (11)0.0144 (3)
C10.3576 (2)0.98834 (18)0.77580 (12)0.0130 (3)
C20.2022 (2)1.01001 (19)0.83015 (13)0.0153 (3)
C30.1135 (2)1.12951 (19)0.80771 (13)0.0161 (3)
C40.1734 (2)1.23192 (19)0.73288 (13)0.0174 (3)
C50.3223 (2)1.21203 (19)0.67852 (13)0.0163 (3)
C60.4145 (2)1.08892 (18)0.69952 (12)0.0138 (3)
C70.6577 (2)0.95245 (18)0.65899 (12)0.0144 (3)
C80.6082 (2)0.85283 (17)0.73720 (12)0.0135 (3)
C90.4607 (2)0.86836 (17)0.79479 (12)0.0128 (3)
C100.4060 (2)0.76276 (17)0.87655 (12)0.0131 (3)
C110.5030 (2)0.78222 (19)0.96875 (13)0.0165 (3)
C120.4476 (2)0.6859 (2)1.04564 (13)0.0178 (3)
C130.2988 (2)0.56871 (19)1.02989 (14)0.0184 (3)
C140.2033 (2)0.54837 (19)0.93779 (14)0.0185 (3)
C150.2549 (2)0.64550 (19)0.86090 (13)0.0163 (3)
C160.8098 (2)0.9359 (2)0.59146 (14)0.0191 (3)
C170.7189 (2)0.72549 (19)0.75589 (13)0.0157 (3)
C180.6537 (3)0.5756 (2)0.69949 (16)0.0243 (4)
S10.21895 (5)0.66550 (5)0.53846 (3)0.01523 (10)
O30.22537 (17)0.50022 (14)0.54897 (10)0.0226 (3)
O20.09255 (19)0.67613 (15)0.44494 (10)0.0218 (3)
O40.14599 (19)0.73228 (17)0.62452 (10)0.0284 (3)
O50.39820 (17)0.74590 (14)0.51153 (10)0.0217 (3)
H2A0.158 (3)0.941 (2)0.8811 (15)0.014 (5)*
H4A0.108 (3)1.313 (2)0.7209 (16)0.024 (5)*
H5A0.363 (3)1.281 (2)0.6270 (16)0.023 (5)*
H11A0.606 (3)0.861 (2)0.9797 (16)0.023 (5)*
H12A0.513 (3)0.700 (2)1.1086 (16)0.019 (5)*
H13A0.258 (3)0.501 (2)1.0818 (17)0.026 (6)*
H14A0.100 (3)0.468 (2)0.9267 (16)0.025 (5)*
H15A0.189 (3)0.634 (2)0.7994 (15)0.016 (5)*
H18A0.736 (3)0.507 (3)0.7149 (18)0.038 (7)*
H18B0.536 (3)0.538 (3)0.7207 (18)0.032 (6)*
H18C0.641 (3)0.587 (3)0.631 (2)0.039 (7)*
H16A0.772 (4)0.847 (3)0.548 (2)0.057 (8)*
H16B0.838 (4)1.017 (3)0.552 (2)0.042 (7)*
H16C0.921 (4)0.922 (3)0.6250 (19)0.039 (7)*
H1N10.592 (3)1.124 (3)0.5945 (18)0.032 (6)*
H1O2−0.001 (5)0.624 (4)0.447 (2)0.070 (11)*

Atomic displacement parameters (Å2)

U11U22U33U12U13U23
Cl10.01539 (19)0.0206 (2)0.0306 (2)0.00572 (15)0.00463 (16)−0.00319 (17)
O10.0157 (6)0.0233 (6)0.0296 (7)0.0043 (5)−0.0031 (5)0.0052 (5)
N10.0154 (6)0.0136 (6)0.0140 (7)0.0013 (5)0.0007 (5)0.0032 (5)
C10.0121 (7)0.0123 (7)0.0143 (7)0.0013 (5)−0.0003 (6)−0.0004 (6)
C20.0130 (7)0.0154 (7)0.0168 (8)0.0004 (6)0.0000 (6)−0.0004 (6)
C30.0126 (7)0.0169 (7)0.0186 (8)0.0031 (6)−0.0001 (6)−0.0042 (6)
C40.0193 (8)0.0147 (7)0.0188 (8)0.0057 (6)−0.0043 (6)−0.0009 (6)
C50.0185 (8)0.0147 (7)0.0155 (8)0.0027 (6)−0.0027 (6)0.0003 (6)
C60.0140 (7)0.0133 (7)0.0136 (8)0.0011 (6)−0.0002 (6)−0.0004 (6)
C70.0129 (7)0.0148 (7)0.0147 (8)0.0004 (6)−0.0006 (6)0.0001 (6)
C80.0130 (7)0.0124 (7)0.0149 (8)0.0015 (6)−0.0005 (6)0.0007 (6)
C90.0123 (7)0.0123 (7)0.0129 (7)−0.0002 (6)−0.0015 (6)−0.0011 (6)
C100.0124 (7)0.0128 (7)0.0151 (8)0.0042 (6)0.0036 (6)0.0017 (6)
C110.0152 (8)0.0163 (7)0.0175 (8)0.0017 (6)−0.0002 (6)0.0006 (6)
C120.0189 (8)0.0219 (8)0.0142 (8)0.0079 (6)0.0006 (6)0.0023 (6)
C130.0211 (8)0.0168 (8)0.0198 (9)0.0078 (6)0.0080 (7)0.0056 (6)
C140.0171 (8)0.0157 (8)0.0221 (9)0.0006 (6)0.0055 (7)0.0013 (6)
C150.0144 (7)0.0180 (8)0.0163 (8)0.0017 (6)0.0002 (6)0.0014 (6)
C160.0170 (8)0.0205 (8)0.0202 (9)0.0028 (7)0.0050 (7)0.0049 (7)
C170.0141 (7)0.0175 (8)0.0168 (8)0.0043 (6)0.0046 (6)0.0052 (6)
C180.0292 (10)0.0202 (9)0.0253 (10)0.0104 (8)−0.0030 (8)−0.0014 (7)
S10.01399 (19)0.01650 (19)0.0145 (2)0.00016 (14)−0.00041 (14)0.00325 (14)
O30.0195 (6)0.0172 (6)0.0317 (7)0.0035 (5)−0.0023 (5)0.0090 (5)
O20.0197 (6)0.0224 (6)0.0219 (7)−0.0004 (5)−0.0081 (5)0.0066 (5)
O40.0267 (7)0.0362 (8)0.0224 (7)0.0081 (6)0.0001 (6)−0.0061 (6)
O50.0152 (6)0.0243 (6)0.0239 (7)−0.0029 (5)−0.0023 (5)0.0094 (5)

Geometric parameters (Å, °)

Cl1—C31.7373 (17)C11—C121.391 (2)
O1—C171.206 (2)C11—H11A0.95 (2)
N1—C71.332 (2)C12—C131.385 (3)
N1—C61.375 (2)C12—H12A0.95 (2)
N1—H1N10.88 (2)C13—C141.386 (3)
C1—C61.410 (2)C13—H13A0.96 (2)
C1—C21.414 (2)C14—C151.390 (2)
C1—C91.433 (2)C14—H14A0.95 (2)
C2—C31.372 (2)C15—H15A0.93 (2)
C2—H2A0.961 (19)C16—H16A0.96 (3)
C3—C41.410 (2)C16—H16B0.91 (3)
C4—C51.369 (2)C16—H16C0.95 (3)
C4—H4A0.95 (2)C17—C181.496 (3)
C5—C61.411 (2)C18—H18A0.95 (3)
C5—H5A0.96 (2)C18—H18B0.94 (3)
C7—C81.414 (2)C18—H18C0.92 (3)
C7—C161.486 (2)S1—O41.4306 (14)
C8—C91.376 (2)S1—O51.4602 (13)
C8—C171.523 (2)S1—O31.4846 (12)
C9—C101.490 (2)S1—O21.5495 (13)
C10—C111.393 (2)O2—H1O20.77 (3)
C10—C151.396 (2)
C7—N1—C6124.00 (14)C10—C11—H11A120.5 (13)
C7—N1—H1N1117.5 (16)C13—C12—C11120.13 (16)
C6—N1—H1N1118.4 (16)C13—C12—H12A120.1 (12)
C6—C1—C2118.86 (14)C11—C12—H12A119.7 (13)
C6—C1—C9118.26 (14)C12—C13—C14120.02 (16)
C2—C1—C9122.87 (15)C12—C13—H13A121.6 (13)
C3—C2—C1118.80 (15)C14—C13—H13A118.4 (14)
C3—C2—H2A120.3 (12)C13—C14—C15120.51 (16)
C1—C2—H2A120.9 (12)C13—C14—H14A120.4 (13)
C2—C3—C4122.16 (16)C15—C14—H14A119.1 (13)
C2—C3—Cl1119.71 (13)C14—C15—C10119.42 (16)
C4—C3—Cl1118.13 (13)C14—C15—H15A121.0 (12)
C5—C4—C3120.02 (15)C10—C15—H15A119.6 (12)
C5—C4—H4A121.3 (13)C7—C16—H16A108.2 (18)
C3—C4—H4A118.7 (13)C7—C16—H16B113.0 (17)
C4—C5—C6118.85 (15)H16A—C16—H16B107 (2)
C4—C5—H5A120.4 (13)C7—C16—H16C114.5 (15)
C6—C5—H5A120.8 (13)H16A—C16—H16C107 (2)
N1—C6—C1118.95 (14)H16B—C16—H16C107 (2)
N1—C6—C5119.76 (14)O1—C17—C18123.85 (16)
C1—C6—C5121.29 (15)O1—C17—C8119.92 (15)
N1—C7—C8118.46 (15)C18—C17—C8116.21 (15)
N1—C7—C16118.53 (15)C17—C18—H18A108.6 (15)
C8—C7—C16123.01 (14)C17—C18—H18B107.4 (15)
C9—C8—C7120.87 (14)H18A—C18—H18B111 (2)
C9—C8—C17120.18 (14)C17—C18—H18C112.1 (15)
C7—C8—C17118.94 (14)H18A—C18—H18C112 (2)
C8—C9—C1119.40 (14)H18B—C18—H18C106 (2)
C8—C9—C10121.29 (14)O4—S1—O5114.16 (8)
C1—C9—C10119.31 (14)O4—S1—O3112.00 (8)
C11—C10—C15120.07 (15)O5—S1—O3110.14 (8)
C11—C10—C9120.25 (14)O4—S1—O2109.30 (8)
C15—C10—C9119.68 (14)O5—S1—O2104.05 (8)
C12—C11—C10119.83 (16)O3—S1—O2106.62 (7)
C12—C11—H11A119.6 (13)S1—O2—H1O2112 (2)
C6—C1—C2—C3−0.9 (2)C7—C8—C9—C10179.22 (15)
C9—C1—C2—C3179.05 (15)C17—C8—C9—C100.3 (2)
C1—C2—C3—C4−0.5 (3)C6—C1—C9—C8−1.4 (2)
C1—C2—C3—Cl1179.14 (12)C2—C1—C9—C8178.66 (15)
C2—C3—C4—C51.3 (3)C6—C1—C9—C10178.62 (14)
Cl1—C3—C4—C5−178.37 (13)C2—C1—C9—C10−1.3 (2)
C3—C4—C5—C6−0.6 (2)C8—C9—C10—C1178.3 (2)
C7—N1—C6—C1−0.2 (2)C1—C9—C10—C11−101.73 (18)
C7—N1—C6—C5−179.97 (15)C8—C9—C10—C15−102.73 (19)
C2—C1—C6—N1−178.14 (14)C1—C9—C10—C1577.3 (2)
C9—C1—C6—N11.9 (2)C15—C10—C11—C12−0.9 (2)
C2—C1—C6—C51.6 (2)C9—C10—C11—C12178.09 (15)
C9—C1—C6—C5−178.35 (15)C10—C11—C12—C131.5 (3)
C4—C5—C6—N1178.89 (15)C11—C12—C13—C14−0.8 (3)
C4—C5—C6—C1−0.8 (2)C12—C13—C14—C15−0.4 (3)
C6—N1—C7—C8−1.9 (2)C13—C14—C15—C101.0 (3)
C6—N1—C7—C16177.43 (15)C11—C10—C15—C14−0.3 (2)
N1—C7—C8—C92.4 (2)C9—C10—C15—C14−179.33 (15)
C16—C7—C8—C9−176.91 (16)C9—C8—C17—O1−89.5 (2)
N1—C7—C8—C17−178.63 (14)C7—C8—C17—O191.6 (2)
C16—C7—C8—C172.0 (2)C9—C8—C17—C1889.0 (2)
C7—C8—C9—C1−0.8 (2)C7—C8—C17—C18−89.93 (19)
C17—C8—C9—C1−179.69 (14)

Hydrogen-bond geometry (Å, °)

D—H···AD—HH···AD···AD—H···A
N1—H1N1···O5i0.88 (2)1.86 (2)2.7200 (19)168 (2)
O2—H1O2···O3ii0.77 (4)1.84 (4)2.6027 (19)180 (5)
C5—H5A···O3iii0.96 (2)2.58 (2)3.304 (2)132.5 (17)
C15—H15A···O40.93 (2)2.55 (2)3.381 (2)148.0 (15)
C16—H16C···O4iv0.95 (3)2.55 (3)3.332 (2)139 (2)
C12—H12A···Cg1v0.95 (2)2.74 (2)3.5884 (18)149.1 (14)

Symmetry codes: (i) −x+1, −y+2, −z+1; (ii) −x, −y+1, −z+1; (iii) x, y+1, z; (iv) x+1, y, z; (v) −x+1, −y+2, −z+2.

Footnotes

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: TK2576).

References

  • Bernstein, J., Davis, R. E., Shimoni, L. & Chang, N.-L. (1995). Angew. Chem. Int. Ed. Engl. 34, 1555–1573.
  • Bruker (2005). APEX2, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.
  • Campbell, S. F., Hardstone, J. D. & Palmer, M. J. (1988). J. Med. Chem. 31, 1031–1035. [PubMed]
  • Chen, Y.-L., Fang, K.-C., Sheu, J.-Y., Hsu, S.-L. & Tzeng, C.-C. (2001). J. Med. Chem. 44, 2374–2377. [PubMed]
  • Cosier, J. & Glazer, A. M. (1986). J. Appl. Cryst. 19, 105–107.
  • Fun, H.-K., Loh, W.-S., Sarveswari, S., Vijayakumar, V. & Reddy, B. P. (2009). Acta Cryst. E65, o2688–o2689. [PMC free article] [PubMed]
  • Kalluraya, B. & Sreenivasa, S. (1998). Il Farmaco, 53, 399–404. [PubMed]
  • Maguire, M. P., Sheets, K. R., McVety, K., Spada, A. P. & Zilberstein, A. (1994). J. Med. Chem. 37, 2129–2137. [PubMed]
  • Markees, D. G., Dewey, V. C. & Kidder, G. W. (1970). J. Med. Chem. 13, 324–326. [PubMed]
  • Michael, J. P. (1997). Nat. Prod. Rep. 14, 605–608.
  • Morimoto, Y., Matsuda, F. & Shirahama, H. (1991). Synlett, 3, 202–203.
  • Roma, G., Braccio, M. D., Grossi, G., Mattioli, F. & Ghia, M. (2000). Eur. J. Med. Chem. 35, 1021–1026. [PubMed]
  • Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. [PubMed]
  • Spek, A. L. (2009). Acta Cryst. D65, 148–155. [PMC free article] [PubMed]

Articles from Acta Crystallographica Section E: Structure Reports Online are provided here courtesy of International Union of Crystallography