Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536807029108/nc2038sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S1600536807029108/nc2038Isup2.hkl |
CCDC reference: 655016
α-Artemether (C16H26O5) was obtained in the pure form from Strides Arco Labs, Mangalore, India. X-ray diffraction quality crystals were grown from acetone (m.p.: 361 K).
All H atoms were initially located in a difference Fourier map. The methyl H atoms were then constrained to an ideal geometry with C—H distances of 0.98 Å and Uiso(H) = 1.5Ueq(C), but each group was allowed to rotate freely about its C—C bond. All other H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms with C—H distances in the range 0.95–1.00 Å and Uiso(H) = 1.2Ueq(C). The amine H was idealized with an N—H distance of 0.86 Å and Uiso(H) = 1.2Ueq(N). Because no strong anomalous scattering atoms are present, the Friedel pairs were merged in the refinement.
Artemisinin and its derivatives, dihydroartemisinin, artemether, arteether and artesunate are antimalarial drugs which possess bioactivity with less toxicity (Wu & Li, 1995). Artemisinin is isolated from the leaves of plant Artemisia annua (Qinghao). It is a sesquiterpene lactone with an endoperoxide linkage. Artemisinin derivatives are more potent than artemisinin and are active by virtue of the endoperoxide. Because of their activity against strains of the parasite that has become resistant to conventional chloroquine therapy and due to the ability due to its lipophilic structure to cross the blood brain barrier, they are particularly effective for the deadly cerebral malaria (Shen & Zhuang, 1984). With their shorter life time and decreasing activity, they are used in combination with other antimalarial drugs. However, some derivatives of artimisinine showed moderate cytotoxicity in vitro. The electronegativity and bulk of the substituents attached to the aryl group plays an insignificant role in cytotoxicity. The endoperoxide moiety present in some sesquiterpenoids plays an important role in antimalarial activity. Its 1,2,4 trioxane ring is unique in nature. After being opened in the plasmodium it liberates singlet oxygen and forms free radicals which in turn produces oxidative damage to the parasites membrane. Artemisinin is hydrophobic in nature and is partitioned into the membrane of the plasmodium. In view of the importance of the title compound (I), C23H24O5, as an antimalarial drug, this paper reports its crystal structure.
The six-membered cyclohexane ring (A, C1—C6) is a slightly distorted chair, with Cremer & Pople (1975) puckering parameters Q, θ and φ of 0.5395 (13) Å, 172.41 (14)° and 314.6 (10)°, respectively. The tetrahydropyran group (D, C1—C2—C12—C11—O2—C10) has a normal chair configuration with puckering parameters Q, θ and φ of 0.5512 (11) Å, 177.68 (11)° and 124 (3)°, respectively. For an ideal chair θ has a value of 0 or 180°. Similar conformations for rings A and D were found in 9,10-dehydrodeoxyartemisinin (Shu-Hui Li et al., 2006). The seven-membered ring B (C1/C6—C9/O1—C10) contains the important peroxy linkage [O3—O4 = 1.4745 (14) Å]. The six-membered ring C (O1—C9—O3—O4—C1—C10) which contains both an oxygen bridge and a peroxy bridge is best described by a twist-boat conformation with puckering parameters Q, θ and φ of 0.7460 (11) Å, 94.05 (8)° and 276.11 (7)°, respectively. For an ideal twist-boat conformation, θ and φ are 90° and (60n + 30)°, respectively. This conformation is consistent with both 9,10-dehydrodeoxyartemisinin (Shu-Hui Li et al.,(2006) and dihydroartemisinin (Qinghaosu Research Group, 1980).
For crystal structures of similar compounds, see: Flippen-Anderson et al. (1989); Yue et al. (2006); Li et al. (2006); Karle & Lin (1995).
For biological activity of artemisinin derivatives in vitro and in vivo, see: Li et al. (2001); Yang et al. (1997); Grace et al. (1998); Maggs et al. (2000).
For endoperoxide sesquiterpene lactone derivatives, see: Venugopalan et al. (1995); Wu et al. (2001); Saxena et al. (2003).
For synthesis of artemisinin and its derivatives, see: Lui et al. (1979); Liu (1980); Robert et al. (2001).
For related literature, see: Allen et al. (1987); Cremer & Pople (1975); Lisgarten et al. (1998); Qinghaosu Research Group (1980); Shen & Zhuang (1984); Wu & Li (1995).
Data collection: APEX2 (Bruker, 2006); cell refinement: APEX2; data reduction: SAINT (Bruker, 2006); program(s) used to solve structure: SHELXS90 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: SHELXTL (Bruker, 2000).
Fig. 1. ORTEP view of α-artemether, (I), showing the atom numbering scheme and 50% probability displacement ellipsoids. |
C16H26O5 | Dx = 1.274 Mg m−3 |
Mr = 298.37 | Mo Kα radiation, λ = 0.71073 Å |
Orthorhombic, P212121 | Cell parameters from 7832 reflections |
a = 10.315 (2) Å | θ = 2.4–29.3° |
b = 13.620 (3) Å | µ = 0.09 mm−1 |
c = 11.073 (2) Å | T = 103 K |
V = 1555.6 (5) Å3 | Chunk, colorless |
Z = 4 | 0.84 × 0.47 × 0.34 mm |
F(000) = 648 |
Bruker APEX II CCD area-detector diffractometer | 2434 independent reflections |
Radiation source: fine-focus sealed tube | 2305 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.029 |
φ and ω scans | θmax = 29.4°, θmin = 2.4° |
Absorption correction: multi-scan (SADABS; Sheldrick, 1996) | h = −14→14 |
Tmin = 0.926, Tmax = 0.969 | k = −18→18 |
17053 measured reflections | l = −15→15 |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.033 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.087 | All H-atom parameters refined |
S = 1.12 | w = 1/[σ2(Fo2) + (0.0581P)2 + 0.1127P] where P = (Fo2 + 2Fc2)/3 |
2434 reflections | (Δ/σ)max = 0.010 |
294 parameters | Δρmax = 0.38 e Å−3 |
0 restraints | Δρmin = −0.18 e Å−3 |
C16H26O5 | V = 1555.6 (5) Å3 |
Mr = 298.37 | Z = 4 |
Orthorhombic, P212121 | Mo Kα radiation |
a = 10.315 (2) Å | µ = 0.09 mm−1 |
b = 13.620 (3) Å | T = 103 K |
c = 11.073 (2) Å | 0.84 × 0.47 × 0.34 mm |
Bruker APEX II CCD area-detector diffractometer | 2434 independent reflections |
Absorption correction: multi-scan (SADABS; Sheldrick, 1996) | 2305 reflections with I > 2σ(I) |
Tmin = 0.926, Tmax = 0.969 | Rint = 0.029 |
17053 measured reflections |
R[F2 > 2σ(F2)] = 0.033 | 0 restraints |
wR(F2) = 0.087 | All H-atom parameters refined |
S = 1.12 | Δρmax = 0.38 e Å−3 |
2434 reflections | Δρmin = −0.18 e Å−3 |
294 parameters |
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. |
x | y | z | Uiso*/Ueq | ||
O1 | 0.03875 (10) | 0.94372 (8) | 0.46788 (9) | 0.0190 (2) | |
O2 | 0.06904 (10) | 0.86438 (8) | 0.29146 (9) | 0.0185 (2) | |
O3 | 0.25631 (10) | 0.96669 (7) | 0.41839 (9) | 0.0190 (2) | |
O4 | 0.29685 (9) | 0.86551 (7) | 0.44698 (9) | 0.0178 (2) | |
O5 | 0.09732 (10) | 0.80257 (9) | 0.10277 (9) | 0.0226 (2) | |
C1 | 0.18559 (12) | 0.80176 (10) | 0.46874 (12) | 0.0153 (2) | |
C2 | 0.21488 (13) | 0.70667 (10) | 0.39781 (13) | 0.0169 (3) | |
H2A | 0.3047 (19) | 0.6846 (15) | 0.4181 (18) | 0.023 (5)* | |
C3 | 0.12631 (15) | 0.62201 (11) | 0.43812 (14) | 0.0217 (3) | |
H3A | 0.032 (2) | 0.6358 (17) | 0.417 (2) | 0.032 (5)* | |
H3B | 0.154 (2) | 0.5623 (17) | 0.397 (2) | 0.029 (5)* | |
C4 | 0.13763 (17) | 0.60375 (12) | 0.57331 (15) | 0.0245 (3) | |
H4A | 0.219 (3) | 0.584 (2) | 0.585 (2) | 0.052 (8)* | |
H4B | 0.081 (2) | 0.5502 (16) | 0.5970 (19) | 0.025 (5)* | |
C5 | 0.10231 (14) | 0.69445 (12) | 0.64718 (14) | 0.0221 (3) | |
H5A | 0.008 (2) | 0.7114 (16) | 0.6347 (18) | 0.026 (5)* | |
C6 | 0.18230 (13) | 0.78510 (11) | 0.60788 (12) | 0.0179 (3) | |
H6A | 0.274 (2) | 0.7701 (16) | 0.6266 (19) | 0.029 (5)* | |
C7 | 0.14016 (15) | 0.87730 (12) | 0.67833 (13) | 0.0216 (3) | |
H7A | 0.049 (2) | 0.8827 (16) | 0.6777 (19) | 0.026 (5)* | |
H7B | 0.169 (2) | 0.8672 (16) | 0.762 (2) | 0.029 (5)* | |
C8 | 0.19185 (15) | 0.97536 (12) | 0.63154 (13) | 0.0216 (3) | |
H8A | 0.282 (2) | 0.9778 (17) | 0.640 (2) | 0.034 (5)* | |
H8B | 0.1549 (19) | 1.0310 (15) | 0.6778 (18) | 0.023 (5)* | |
C9 | 0.15630 (14) | 0.99552 (11) | 0.49904 (13) | 0.0190 (3) | |
C10 | 0.06182 (13) | 0.85073 (10) | 0.41870 (13) | 0.0160 (3) | |
H10A | −0.0143 (17) | 0.8105 (14) | 0.4358 (16) | 0.013 (4)* | |
C11 | 0.08704 (13) | 0.77595 (11) | 0.22462 (12) | 0.0174 (3) | |
H11A | 0.0109 (18) | 0.7349 (14) | 0.2375 (15) | 0.011 (4)* | |
C12 | 0.21300 (13) | 0.72559 (10) | 0.26021 (12) | 0.0176 (3) | |
H12A | 0.2810 (19) | 0.7722 (13) | 0.2414 (16) | 0.015 (4)* | |
C13 | 0.1210 (2) | 0.67245 (16) | 0.78169 (16) | 0.0353 (4) | |
H13A | 0.074 (2) | 0.6122 (19) | 0.804 (2) | 0.041 (6)* | |
H13B | 0.088 (2) | 0.7235 (19) | 0.835 (2) | 0.044 (7)* | |
H13C | 0.208 (3) | 0.664 (2) | 0.800 (2) | 0.054 (8)* | |
C14 | 0.13381 (18) | 1.10288 (11) | 0.46909 (15) | 0.0247 (3) | |
H14A | 0.128 (2) | 1.1111 (14) | 0.3787 (19) | 0.023 (5)* | |
H14B | 0.204 (2) | 1.1413 (17) | 0.499 (2) | 0.033 (6)* | |
H14C | 0.054 (2) | 1.1227 (19) | 0.508 (2) | 0.040 (6)* | |
C15 | −0.01422 (18) | 0.85153 (13) | 0.05639 (15) | 0.0274 (3) | |
H15A | 0.001 (2) | 0.8640 (18) | −0.025 (2) | 0.037 (6)* | |
H15B | −0.023 (2) | 0.9115 (18) | 0.093 (2) | 0.036 (6)* | |
H15C | −0.093 (2) | 0.8117 (19) | 0.070 (2) | 0.040 (6)* | |
C16 | 0.23452 (16) | 0.63220 (12) | 0.18597 (15) | 0.0255 (3) | |
H16A | 0.308 (2) | 0.5962 (16) | 0.214 (2) | 0.034 (6)* | |
H16B | 0.249 (2) | 0.6487 (17) | 0.102 (2) | 0.036 (6)* | |
H16C | 0.162 (2) | 0.5883 (17) | 0.194 (2) | 0.032 (6)* |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.0164 (4) | 0.0208 (5) | 0.0198 (5) | 0.0027 (4) | −0.0010 (4) | −0.0062 (4) |
O2 | 0.0221 (5) | 0.0187 (5) | 0.0148 (4) | 0.0025 (4) | −0.0020 (4) | −0.0035 (4) |
O3 | 0.0203 (5) | 0.0174 (5) | 0.0195 (4) | −0.0003 (4) | 0.0030 (4) | 0.0000 (4) |
O4 | 0.0128 (4) | 0.0173 (4) | 0.0233 (5) | −0.0006 (4) | 0.0008 (4) | 0.0007 (4) |
O5 | 0.0253 (5) | 0.0278 (5) | 0.0146 (4) | 0.0030 (4) | −0.0013 (4) | −0.0020 (4) |
C1 | 0.0119 (5) | 0.0184 (6) | 0.0157 (6) | −0.0011 (5) | 0.0001 (5) | −0.0007 (5) |
C2 | 0.0142 (6) | 0.0176 (6) | 0.0189 (6) | 0.0006 (5) | 0.0007 (5) | −0.0013 (5) |
C3 | 0.0236 (7) | 0.0178 (6) | 0.0238 (7) | −0.0032 (5) | 0.0012 (6) | −0.0003 (5) |
C4 | 0.0261 (7) | 0.0221 (7) | 0.0253 (7) | −0.0017 (6) | 0.0003 (6) | 0.0055 (6) |
C5 | 0.0201 (6) | 0.0266 (7) | 0.0198 (6) | −0.0046 (6) | 0.0014 (6) | 0.0022 (6) |
C6 | 0.0142 (6) | 0.0244 (7) | 0.0151 (6) | −0.0022 (5) | −0.0014 (5) | 0.0009 (5) |
C7 | 0.0203 (7) | 0.0286 (7) | 0.0158 (6) | −0.0024 (6) | 0.0008 (5) | −0.0027 (5) |
C8 | 0.0234 (7) | 0.0249 (7) | 0.0165 (6) | −0.0031 (6) | −0.0017 (6) | −0.0046 (5) |
C9 | 0.0187 (6) | 0.0203 (6) | 0.0181 (6) | −0.0007 (5) | 0.0000 (5) | −0.0043 (5) |
C10 | 0.0131 (5) | 0.0190 (6) | 0.0158 (6) | 0.0011 (5) | −0.0007 (5) | −0.0032 (5) |
C11 | 0.0184 (6) | 0.0184 (6) | 0.0152 (6) | 0.0009 (5) | −0.0003 (5) | −0.0037 (5) |
C12 | 0.0154 (6) | 0.0192 (6) | 0.0182 (6) | 0.0005 (5) | 0.0022 (5) | −0.0033 (5) |
C13 | 0.0449 (11) | 0.0397 (10) | 0.0215 (7) | −0.0108 (8) | 0.0022 (8) | 0.0063 (7) |
C14 | 0.0302 (8) | 0.0199 (7) | 0.0240 (7) | 0.0018 (6) | −0.0002 (6) | −0.0043 (6) |
C15 | 0.0338 (8) | 0.0284 (8) | 0.0200 (7) | 0.0081 (7) | −0.0053 (7) | −0.0011 (6) |
C16 | 0.0272 (7) | 0.0245 (7) | 0.0248 (7) | 0.0052 (6) | 0.0035 (6) | −0.0072 (6) |
O1—C10 | 1.3990 (17) | C6—H6A | 0.99 (2) |
O1—C9 | 1.4447 (17) | C7—C8 | 1.529 (2) |
O2—C10 | 1.4231 (16) | C7—H7A | 0.94 (2) |
O2—C11 | 1.4258 (17) | C7—H7B | 0.98 (2) |
O3—C9 | 1.4198 (17) | C8—C9 | 1.537 (2) |
O3—O4 | 1.4745 (14) | C8—H8A | 0.94 (2) |
O4—C1 | 1.4591 (16) | C8—H8B | 0.99 (2) |
O5—C11 | 1.4011 (17) | C9—C14 | 1.517 (2) |
O5—C15 | 1.426 (2) | C10—H10A | 0.976 (18) |
C1—C10 | 1.5434 (18) | C11—C12 | 1.5211 (19) |
C1—C2 | 1.5445 (19) | C11—H11A | 0.974 (19) |
C1—C6 | 1.5576 (19) | C12—C16 | 1.531 (2) |
C2—C3 | 1.537 (2) | C12—H12A | 0.969 (19) |
C2—C12 | 1.5454 (19) | C13—H13A | 0.98 (3) |
C2—H2A | 1.00 (2) | C13—H13B | 0.97 (3) |
C3—C4 | 1.522 (2) | C13—H13C | 0.92 (3) |
C3—H3A | 1.02 (2) | C14—H14A | 1.01 (2) |
C3—H3B | 0.97 (2) | C14—H14B | 0.95 (2) |
C4—C5 | 1.526 (2) | C14—H14C | 0.97 (3) |
C4—H4A | 0.89 (3) | C15—H15A | 0.93 (3) |
C4—H4B | 0.97 (2) | C15—H15B | 0.92 (2) |
C5—C13 | 1.531 (2) | C15—H15C | 0.99 (2) |
C5—C6 | 1.547 (2) | C16—H16A | 0.96 (2) |
C5—H5A | 1.01 (2) | C16—H16B | 0.97 (2) |
C6—C7 | 1.541 (2) | C16—H16C | 0.97 (2) |
C10—O1—C9 | 113.10 (10) | C9—C8—H8B | 105.4 (11) |
C10—O2—C11 | 114.23 (11) | H8A—C8—H8B | 107.7 (19) |
C9—O3—O4 | 109.24 (10) | O3—C9—O1 | 108.94 (11) |
C1—O4—O3 | 111.62 (9) | O3—C9—C14 | 103.90 (12) |
C11—O5—C15 | 114.01 (12) | O1—C9—C14 | 106.87 (12) |
O4—C1—C10 | 109.52 (11) | O3—C9—C8 | 112.19 (12) |
O4—C1—C2 | 105.14 (10) | O1—C9—C8 | 109.93 (12) |
C10—C1—C2 | 109.97 (11) | C14—C9—C8 | 114.66 (12) |
O4—C1—C6 | 105.50 (10) | O1—C10—O2 | 106.03 (11) |
C10—C1—C6 | 113.58 (11) | O1—C10—C1 | 113.09 (11) |
C2—C1—C6 | 112.65 (11) | O2—C10—C1 | 111.63 (10) |
C3—C2—C12 | 113.82 (11) | O1—C10—H10A | 107.2 (11) |
C3—C2—C1 | 111.41 (11) | O2—C10—H10A | 107.9 (10) |
C12—C2—C1 | 111.05 (11) | C1—C10—H10A | 110.7 (11) |
C3—C2—H2A | 105.1 (12) | O5—C11—O2 | 106.93 (11) |
C12—C2—H2A | 106.5 (12) | O5—C11—C12 | 107.55 (11) |
C1—C2—H2A | 108.6 (12) | O2—C11—C12 | 110.95 (11) |
C4—C3—C2 | 111.26 (12) | O5—C11—H11A | 110.5 (10) |
C4—C3—H3A | 109.5 (13) | O2—C11—H11A | 107.6 (10) |
C2—C3—H3A | 111.2 (13) | C12—C11—H11A | 113.1 (11) |
C4—C3—H3B | 107.2 (13) | C11—C12—C16 | 111.06 (12) |
C2—C3—H3B | 108.6 (14) | C11—C12—C2 | 109.96 (11) |
H3A—C3—H3B | 109.0 (18) | C16—C12—C2 | 112.90 (12) |
C3—C4—C5 | 112.13 (13) | C11—C12—H12A | 105.5 (11) |
C3—C4—H4A | 105.5 (18) | C16—C12—H12A | 108.9 (11) |
C5—C4—H4A | 112.9 (18) | C2—C12—H12A | 108.2 (10) |
C3—C4—H4B | 110.0 (12) | C5—C13—H13A | 110.0 (15) |
C5—C4—H4B | 108.6 (13) | C5—C13—H13B | 113.9 (15) |
H4A—C4—H4B | 108 (2) | H13A—C13—H13B | 106 (2) |
C4—C5—C13 | 109.45 (15) | C5—C13—H13C | 111.1 (17) |
C4—C5—C6 | 111.58 (12) | H13A—C13—H13C | 109 (2) |
C13—C5—C6 | 111.26 (14) | H13B—C13—H13C | 107 (2) |
C4—C5—H5A | 110.0 (12) | C9—C14—H14A | 109.5 (11) |
C13—C5—H5A | 107.4 (12) | C9—C14—H14B | 109.8 (14) |
C6—C5—H5A | 107.0 (12) | H14A—C14—H14B | 109.2 (19) |
C7—C6—C5 | 110.94 (12) | C9—C14—H14C | 107.5 (15) |
C7—C6—C1 | 112.84 (12) | H14A—C14—H14C | 111 (2) |
C5—C6—C1 | 113.96 (12) | H14B—C14—H14C | 110 (2) |
C7—C6—H6A | 109.3 (13) | O5—C15—H15A | 107.2 (15) |
C5—C6—H6A | 106.6 (13) | O5—C15—H15B | 109.5 (15) |
C1—C6—H6A | 102.5 (12) | H15A—C15—H15B | 107 (2) |
C8—C7—C6 | 116.24 (12) | O5—C15—H15C | 110.8 (14) |
C8—C7—H7A | 106.1 (13) | H15A—C15—H15C | 113 (2) |
C6—C7—H7A | 109.9 (13) | H15B—C15—H15C | 110 (2) |
C8—C7—H7B | 109.7 (13) | C12—C16—H16A | 111.5 (14) |
C6—C7—H7B | 106.2 (13) | C12—C16—H16B | 110.2 (14) |
H7A—C7—H7B | 108.5 (18) | H16A—C16—H16B | 108 (2) |
C7—C8—C9 | 113.35 (12) | C12—C16—H16C | 110.5 (14) |
C7—C8—H8A | 110.1 (15) | H16A—C16—H16C | 105.7 (17) |
C9—C8—H8A | 109.1 (15) | H16B—C16—H16C | 111 (2) |
C7—C8—H8B | 111.0 (11) | ||
C9—O3—O4—C1 | 43.92 (13) | O4—O3—C9—C8 | 49.83 (14) |
O3—O4—C1—C10 | 16.81 (13) | C10—O1—C9—O3 | 30.95 (16) |
O3—O4—C1—C2 | 134.93 (10) | C10—O1—C9—C14 | 142.63 (12) |
O3—O4—C1—C6 | −105.80 (11) | C10—O1—C9—C8 | −92.36 (13) |
O4—C1—C2—C3 | 164.58 (11) | C7—C8—C9—O3 | −95.08 (15) |
C10—C1—C2—C3 | −77.60 (14) | C7—C8—C9—O1 | 26.31 (17) |
C6—C1—C2—C3 | 50.20 (15) | C7—C8—C9—C14 | 146.71 (14) |
O4—C1—C2—C12 | −67.41 (13) | C9—O1—C10—O2 | −91.32 (12) |
C10—C1—C2—C12 | 50.41 (14) | C9—O1—C10—C1 | 31.32 (15) |
C6—C1—C2—C12 | 178.20 (11) | C11—O2—C10—O1 | −177.53 (10) |
C12—C2—C3—C4 | 177.13 (12) | C11—O2—C10—C1 | 58.91 (14) |
C1—C2—C3—C4 | −56.37 (16) | O4—C1—C10—O1 | −57.04 (14) |
C2—C3—C4—C5 | 58.87 (17) | C2—C1—C10—O1 | −172.11 (11) |
C3—C4—C5—C13 | −177.72 (14) | C6—C1—C10—O1 | 60.61 (15) |
C3—C4—C5—C6 | −54.13 (18) | O4—C1—C10—O2 | 62.43 (14) |
C4—C5—C6—C7 | 176.82 (12) | C2—C1—C10—O2 | −52.64 (14) |
C13—C5—C6—C7 | −60.62 (18) | C6—C1—C10—O2 | −179.92 (11) |
C4—C5—C6—C1 | 48.15 (17) | C15—O5—C11—O2 | −60.39 (15) |
C13—C5—C6—C1 | 170.71 (14) | C15—O5—C11—C12 | −179.62 (12) |
O4—C1—C6—C7 | 71.41 (14) | C10—O2—C11—O5 | −177.65 (11) |
C10—C1—C6—C7 | −48.55 (15) | C10—O2—C11—C12 | −60.64 (14) |
C2—C1—C6—C7 | −174.43 (11) | O5—C11—C12—C16 | −61.73 (15) |
O4—C1—C6—C5 | −160.89 (11) | O2—C11—C12—C16 | −178.35 (12) |
C10—C1—C6—C5 | 79.14 (15) | O5—C11—C12—C2 | 172.58 (11) |
C2—C1—C6—C5 | −46.73 (16) | O2—C11—C12—C2 | 55.96 (15) |
C5—C6—C7—C8 | −168.34 (12) | C3—C2—C12—C11 | 74.34 (14) |
C1—C6—C7—C8 | −39.08 (17) | C1—C2—C12—C11 | −52.34 (15) |
C6—C7—C8—C9 | 57.24 (17) | C3—C2—C12—C16 | −50.30 (17) |
O4—O3—C9—O1 | −72.13 (13) | C1—C2—C12—C16 | −176.99 (11) |
O4—O3—C9—C14 | 174.24 (10) |
Experimental details
Crystal data | |
Chemical formula | C16H26O5 |
Mr | 298.37 |
Crystal system, space group | Orthorhombic, P212121 |
Temperature (K) | 103 |
a, b, c (Å) | 10.315 (2), 13.620 (3), 11.073 (2) |
V (Å3) | 1555.6 (5) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.09 |
Crystal size (mm) | 0.84 × 0.47 × 0.34 |
Data collection | |
Diffractometer | Bruker APEX II CCD area-detector |
Absorption correction | Multi-scan (SADABS; Sheldrick, 1996) |
Tmin, Tmax | 0.926, 0.969 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 17053, 2434, 2305 |
Rint | 0.029 |
(sin θ/λ)max (Å−1) | 0.691 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.033, 0.087, 1.12 |
No. of reflections | 2434 |
No. of parameters | 294 |
H-atom treatment | All H-atom parameters refined |
Δρmax, Δρmin (e Å−3) | 0.38, −0.18 |
Computer programs: APEX2 (Bruker, 2006), APEX2, SAINT (Bruker, 2006), SHELXS90 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), ORTEP-3 (Farrugia, 1997), SHELXTL (Bruker, 2000).
Artemisinin and its derivatives, dihydroartemisinin, artemether, arteether and artesunate are antimalarial drugs which possess bioactivity with less toxicity (Wu & Li, 1995). Artemisinin is isolated from the leaves of plant Artemisia annua (Qinghao). It is a sesquiterpene lactone with an endoperoxide linkage. Artemisinin derivatives are more potent than artemisinin and are active by virtue of the endoperoxide. Because of their activity against strains of the parasite that has become resistant to conventional chloroquine therapy and due to the ability due to its lipophilic structure to cross the blood brain barrier, they are particularly effective for the deadly cerebral malaria (Shen & Zhuang, 1984). With their shorter life time and decreasing activity, they are used in combination with other antimalarial drugs. However, some derivatives of artimisinine showed moderate cytotoxicity in vitro. The electronegativity and bulk of the substituents attached to the aryl group plays an insignificant role in cytotoxicity. The endoperoxide moiety present in some sesquiterpenoids plays an important role in antimalarial activity. Its 1,2,4 trioxane ring is unique in nature. After being opened in the plasmodium it liberates singlet oxygen and forms free radicals which in turn produces oxidative damage to the parasites membrane. Artemisinin is hydrophobic in nature and is partitioned into the membrane of the plasmodium. In view of the importance of the title compound (I), C23H24O5, as an antimalarial drug, this paper reports its crystal structure.
The six-membered cyclohexane ring (A, C1—C6) is a slightly distorted chair, with Cremer & Pople (1975) puckering parameters Q, θ and φ of 0.5395 (13) Å, 172.41 (14)° and 314.6 (10)°, respectively. The tetrahydropyran group (D, C1—C2—C12—C11—O2—C10) has a normal chair configuration with puckering parameters Q, θ and φ of 0.5512 (11) Å, 177.68 (11)° and 124 (3)°, respectively. For an ideal chair θ has a value of 0 or 180°. Similar conformations for rings A and D were found in 9,10-dehydrodeoxyartemisinin (Shu-Hui Li et al., 2006). The seven-membered ring B (C1/C6—C9/O1—C10) contains the important peroxy linkage [O3—O4 = 1.4745 (14) Å]. The six-membered ring C (O1—C9—O3—O4—C1—C10) which contains both an oxygen bridge and a peroxy bridge is best described by a twist-boat conformation with puckering parameters Q, θ and φ of 0.7460 (11) Å, 94.05 (8)° and 276.11 (7)°, respectively. For an ideal twist-boat conformation, θ and φ are 90° and (60n + 30)°, respectively. This conformation is consistent with both 9,10-dehydrodeoxyartemisinin (Shu-Hui Li et al.,(2006) and dihydroartemisinin (Qinghaosu Research Group, 1980).