research communications
Artemisia reticulata
of a bioactive sesquiterpene isolated fromaBioorganic Division, Bhabha Atomic Research Centre, Trombay, Mumbai 85, India, bClemens Schöpf-Institut für Organische, Chemie und Biochemie, Technische Universität Darmstadt, Petersenstrasse 22, D-64287 Darmstadt, Germany, and cAccident & Emergency Department, Franco, Vietnamese Hospital, 7-Nguyen, Luong Bang Street, HoChiMinh City, Vietnam
*Correspondence e-mail: nguyendonhuquynh@yahoo.com
The title compound, C15H24O2 {systematic name: 1-[6-hydroxy-7-(propan-2-yl)-4-methylidene-2,3,3a,4,5,6,7,7a-octahydro-1H-inden-1-yl]ethanone} was isolated from A. reticulata by over silica gel by gradient solvent elution. The molecule comprises a bicyclo[4.3.0]nonane ring bearing acetoxy, hydroxy and isopropyl substituents, and an exocyclic double bond on the cyclohexane ring. In the bicyclic skeleton, the cyclohexane ring adopts a chair conformation ring and the cyclopentane ring is in an In the crystal, molecules are linked by O—H⋯O hydrogen bonds, forming chains along [010]. These chains are cross-linked by C—H⋯O hydrogen bonds.
Keywords: crystal structure; sesquiterpene; isolation; Artemisia reticulata; antiproliferative property.
CCDC reference: 1455684
1. Chemical context
The title compound is a natural product, which has been isolated from the Indian herb A. reticulata by column chromatography over silica gel. A. reticulata (family: Asteraceae) is a traditional herb which has many applications in folklore medicine for conventional therapy against several diseases such as malaria (Klayman et al., 1984; Malagon et al., 1997; Newton & White, 1999), cancer (Efferth et al., 2001; Lai et al., 1995), cardiovascular (Guantai et al., 1999), vasodilatory (Walker, 1996), hepatitis (Aniya et al., 2000) and diabetes (Iriadam et al., 2006). It is found as a constituent in many ayurvedic or herbal drug preparations such as forkolin and Afsanteen in Indian traditional medicinal systems (Nadkarni, 1954; Satyavati et al., 1987; Subramoniam et al., 1996; Drury, 1978). The Artemisia species are a rich source of bioactive sesquiterpenenoids (Klayman et al., 1984) such as artemisinin, artemisin etc. Artimisinin and artemisin are isolated from herbs of the species A. annua (Klayman, 1985) belonging to the sesquiterpene class. The title molecule possesses antiplasmodial activity and it is now under clinical trial for the treatment of malaria. Our group are currently searching for artemisin, artemisinin or their analogues from other varieties of Artemisia species and as part of these studies, the structure of the title compound is now reported.
2. Structural commentary
The molecular structure of the title compound is shown in Fig. 1. The compound comprises fused cyclohexane and cyclopentane rings. It has been substantiated by a positive LB test (Liebermann Burchard Test), which indicates that it belongs to the sesquiterpene class. The compound is soluble in chloroform but has poor solubility in methanol.
The bicyclic skeleton contains one acetyl group at atom C1 of the cyclopentane ring, one isopropyl group and one hydroxyl group located at atoms C6 and C7 in the cyclohexane ring. An exocyclic olefinic double bond is located between atoms C9 and C15 and attached to the cyclohexane ring. The torsion angles C3—C4—C5—C6 and C9—C4—C5—C1 of −169.2 (3) and −170.9 (3)°, respectively, describe the geometry at the junction of the two rings. The C7—C6—C5 and C9—C4—C5 angles are 107.3 (2) and 109.2 (3)°, respectively.
3. Supramolecular features
In the crystal, molecules are linked by O—H⋯O hydrogen bonds, forming chains along [010] (Table 1 and Fig. 2). These chains are cross-linked by weak C—H⋯O hydrogen bonds.
4. Database survey
A search of Cambridge Structural Database (CSD, Version 5.36, last update May 2015; Groom & Allen, 2015) found only one molecule, Pulioplopane A (15-hydroxy-10 (14)-oplopen-4-one; Triana et al., 2005) that has a similar structural skeleton to the title sesquitertene although it is is unrelated in a biochemical sense.
5. Synthesis and crystallization
The title sesquiterpene was isolated as colourless solid from the methanol extract of A. reticulata by over silica gel with a mixture of ethyl acetate and hexane with a followed by preparative thin layer Crystals were obtained after recrystallization three times from ethyl acetate:hexane (1:4) at room temperature by the slow evaporation method. Bioassay of this molecule has been conducted against human ovarian cancer cell line A 2780 and revealed that it possessed significant antiproliferative activity (unpublished results).
6. Refinement
Crystal data, data collection and structure . H atoms were placed in calculated positions with C—H = 0.93–0.98 Å and O—H = 0.82 Å and refined in a riding-motion approximation with Uiso(U) = 1.2Ueq(C,O). No Friedel pairs were collected therefore the could not be determined from the X-ray data and the assignment is arbitrary.
details are summarized in Table 2Supporting information
CCDC reference: 1455684
https://doi.org/10.1107/S2056989016003236/lh5803sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989016003236/lh5803Isup2.hkl
Supporting information file. DOI: https://doi.org/10.1107/S2056989016003236/lh5803Isup3.cml
Data collection: CAD-4-PC (Enraf–Nonius, 1993); cell
CAD-4-PC (Enraf–Nonius, 1993); data reduction: REDU4 (Stoe & Cie, 1987); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).C15H24O2 | F(000) = 260 |
Mr = 236.34 | Dx = 1.123 Mg m−3 |
Monoclinic, P21 | Cu Kα radiation, λ = 1.54180 Å |
Hall symbol: P 2yb | Cell parameters from 25 reflections |
a = 8.849 (4) Å | θ = 5.5–27.1° |
b = 5.336 (1) Å | µ = 0.56 mm−1 |
c = 14.994 (5) Å | T = 299 K |
β = 99.21 (2)° | Rod, colourless |
V = 698.9 (4) Å3 | 0.50 × 0.18 × 0.15 mm |
Z = 2 |
Enraf–Nonius CAD-4 diffractometer | Rint = 0.052 |
Radiation source: fine-focus sealed tube | θmax = 67.0°, θmin = 3.0° |
Graphite monochromator | h = −10→3 |
ω/2θ scans | k = 0→6 |
1916 measured reflections | l = −17→17 |
1392 independent reflections | 3 standard reflections every 120 min |
1260 reflections with I > 2σ(I) | intensity decay: 1.0% |
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)] = 0.060 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.164 | H-atom parameters constrained |
S = 1.10 | w = 1/[σ2(Fo2) + (0.1147P)2 + 0.0812P] where P = (Fo2 + 2Fc2)/3 |
1392 reflections | (Δ/σ)max < 0.001 |
154 parameters | Δρmax = 0.46 e Å−3 |
1 restraint | Δρmin = −0.22 e Å−3 |
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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 | 0.5467 (3) | 0.0974 (5) | 0.03391 (14) | 0.0580 (7) | |
H1O | 0.5259 | 0.2380 | 0.0135 | 0.070* | |
O2 | 0.9664 (3) | 0.1293 (5) | 0.3910 (2) | 0.0680 (8) | |
C1 | 0.8020 (3) | 0.4666 (6) | 0.33401 (19) | 0.0401 (7) | |
H1 | 0.8184 | 0.6168 | 0.2992 | 0.048* | |
C2 | 0.7177 (4) | 0.5402 (8) | 0.4141 (2) | 0.0539 (9) | |
H2A | 0.7821 | 0.5069 | 0.4715 | 0.065* | |
H2B | 0.6912 | 0.7167 | 0.4112 | 0.065* | |
C3 | 0.5742 (4) | 0.3792 (9) | 0.4035 (2) | 0.0568 (9) | |
H3A | 0.5943 | 0.2188 | 0.4335 | 0.068* | |
H3B | 0.4923 | 0.4633 | 0.4277 | 0.068* | |
C4 | 0.5350 (3) | 0.3473 (7) | 0.3022 (2) | 0.0446 (7) | |
H4 | 0.5020 | 0.5109 | 0.2765 | 0.053* | |
C5 | 0.6918 (3) | 0.2887 (5) | 0.27514 (17) | 0.0355 (6) | |
H5 | 0.7191 | 0.1174 | 0.2952 | 0.043* | |
C6 | 0.6880 (3) | 0.2967 (5) | 0.17229 (17) | 0.0370 (7) | |
H6 | 0.6501 | 0.4629 | 0.1518 | 0.044* | |
C7 | 0.5672 (4) | 0.1059 (6) | 0.13003 (18) | 0.0439 (7) | |
H7 | 0.6039 | −0.0600 | 0.1517 | 0.053* | |
C8 | 0.4103 (4) | 0.1446 (9) | 0.1602 (2) | 0.0590 (10) | |
H8A | 0.3654 | 0.2991 | 0.1341 | 0.071* | |
H8B | 0.3429 | 0.0081 | 0.1371 | 0.071* | |
C9 | 0.4206 (4) | 0.1563 (8) | 0.2604 (2) | 0.0508 (8) | |
C10 | 0.9549 (4) | 0.3515 (7) | 0.3722 (2) | 0.0431 (7) | |
C11 | 1.0900 (4) | 0.5203 (9) | 0.3893 (3) | 0.0671 (11) | |
H11A | 1.1664 | 0.4637 | 0.3552 | 0.081* | |
H11B | 1.1313 | 0.5185 | 0.4526 | 0.081* | |
H11C | 1.0594 | 0.6878 | 0.3713 | 0.081* | |
C12 | 0.8473 (4) | 0.2670 (6) | 0.1447 (2) | 0.0447 (8) | |
H12 | 0.9160 | 0.3774 | 0.1847 | 0.054* | |
C13 | 0.8571 (5) | 0.3509 (9) | 0.0487 (2) | 0.0604 (10) | |
H13A | 0.8294 | 0.5246 | 0.0418 | 0.072* | |
H13B | 0.7882 | 0.2524 | 0.0067 | 0.072* | |
H13C | 0.9598 | 0.3286 | 0.0371 | 0.072* | |
C14 | 0.9125 (5) | 0.0040 (8) | 0.1601 (3) | 0.0613 (10) | |
H14A | 0.8454 | −0.1135 | 0.1251 | 0.074* | |
H14B | 0.9217 | −0.0377 | 0.2230 | 0.074* | |
H14C | 1.0116 | −0.0027 | 0.1419 | 0.074* | |
C15 | 0.3418 (5) | 0.0067 (11) | 0.3076 (3) | 0.0708 (12) | |
H15A | 0.2759 | −0.1134 | 0.2780 | 0.085* | |
H15B | 0.3528 | 0.0225 | 0.3701 | 0.085* |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.0792 (15) | 0.0505 (15) | 0.0419 (11) | −0.0110 (14) | 0.0024 (10) | −0.0077 (11) |
O2 | 0.0730 (17) | 0.0337 (14) | 0.0893 (19) | 0.0019 (14) | −0.0110 (13) | 0.0124 (14) |
C1 | 0.0543 (16) | 0.0251 (14) | 0.0392 (13) | −0.0004 (13) | 0.0022 (12) | 0.0020 (12) |
C2 | 0.067 (2) | 0.045 (2) | 0.0479 (16) | 0.0059 (17) | 0.0046 (14) | −0.0101 (16) |
C3 | 0.0614 (19) | 0.063 (2) | 0.0489 (17) | 0.0040 (18) | 0.0176 (14) | −0.0047 (18) |
C4 | 0.0501 (16) | 0.0376 (17) | 0.0472 (16) | 0.0042 (15) | 0.0112 (12) | −0.0022 (14) |
C5 | 0.0451 (14) | 0.0226 (14) | 0.0386 (14) | −0.0002 (12) | 0.0059 (11) | 0.0015 (12) |
C6 | 0.0513 (16) | 0.0226 (14) | 0.0369 (13) | 0.0002 (13) | 0.0064 (11) | 0.0013 (12) |
C7 | 0.0570 (17) | 0.0330 (17) | 0.0410 (14) | −0.0066 (15) | 0.0052 (13) | −0.0001 (14) |
C8 | 0.0527 (18) | 0.062 (3) | 0.0603 (19) | −0.010 (2) | 0.0022 (14) | −0.004 (2) |
C9 | 0.0423 (15) | 0.049 (2) | 0.0626 (18) | −0.0012 (16) | 0.0135 (13) | −0.0002 (17) |
C10 | 0.0516 (17) | 0.0324 (16) | 0.0438 (15) | −0.0007 (14) | 0.0026 (12) | −0.0008 (14) |
C11 | 0.0541 (19) | 0.047 (2) | 0.095 (3) | −0.0055 (18) | −0.0023 (18) | −0.002 (2) |
C12 | 0.0551 (17) | 0.0307 (16) | 0.0492 (17) | −0.0035 (15) | 0.0108 (13) | −0.0007 (14) |
C13 | 0.078 (2) | 0.052 (2) | 0.0559 (19) | −0.004 (2) | 0.0248 (17) | −0.0006 (18) |
C14 | 0.070 (2) | 0.042 (2) | 0.077 (2) | 0.0144 (19) | 0.0264 (18) | 0.0068 (19) |
C15 | 0.060 (2) | 0.076 (3) | 0.080 (2) | −0.014 (2) | 0.0229 (18) | −0.004 (2) |
O1—C7 | 1.424 (3) | C7—C8 | 1.542 (5) |
O1—H1O | 0.8200 | C7—H7 | 0.9800 |
O2—C10 | 1.219 (5) | C8—C9 | 1.493 (5) |
C1—C10 | 1.513 (4) | C8—H8A | 0.9700 |
C1—C5 | 1.535 (4) | C8—H8B | 0.9700 |
C1—C2 | 1.562 (5) | C9—C15 | 1.335 (6) |
C1—H1 | 0.9800 | C10—C11 | 1.486 (5) |
C2—C3 | 1.521 (6) | C11—H11A | 0.9600 |
C2—H2A | 0.9700 | C11—H11B | 0.9600 |
C2—H2B | 0.9700 | C11—H11C | 0.9600 |
C3—C4 | 1.513 (4) | C12—C14 | 1.521 (5) |
C3—H3A | 0.9700 | C12—C13 | 1.523 (5) |
C3—H3B | 0.9700 | C12—H12 | 0.9800 |
C4—C9 | 1.501 (5) | C13—H13A | 0.9600 |
C4—C5 | 1.539 (4) | C13—H13B | 0.9600 |
C4—H4 | 0.9800 | C13—H13C | 0.9600 |
C5—C6 | 1.538 (3) | C14—H14A | 0.9600 |
C5—H5 | 0.9800 | C14—H14B | 0.9600 |
C6—C7 | 1.537 (4) | C14—H14C | 0.9600 |
C6—C12 | 1.540 (4) | C15—H15A | 0.9300 |
C6—H6 | 0.9800 | C15—H15B | 0.9300 |
C7—O1—H1O | 109.5 | C6—C7—H7 | 106.8 |
C10—C1—C5 | 114.5 (3) | C8—C7—H7 | 106.8 |
C10—C1—C2 | 108.6 (2) | C9—C8—C7 | 112.9 (3) |
C5—C1—C2 | 105.1 (2) | C9—C8—H8A | 109.0 |
C10—C1—H1 | 109.5 | C7—C8—H8A | 109.0 |
C5—C1—H1 | 109.5 | C9—C8—H8B | 109.0 |
C2—C1—H1 | 109.5 | C7—C8—H8B | 109.0 |
C3—C2—C1 | 105.8 (3) | H8A—C8—H8B | 107.8 |
C3—C2—H2A | 110.6 | C15—C9—C8 | 123.8 (4) |
C1—C2—H2A | 110.6 | C15—C9—C4 | 124.0 (4) |
C3—C2—H2B | 110.6 | C8—C9—C4 | 112.2 (3) |
C1—C2—H2B | 110.6 | O2—C10—C11 | 121.0 (3) |
H2A—C2—H2B | 108.7 | O2—C10—C1 | 121.3 (3) |
C4—C3—C2 | 102.8 (3) | C11—C10—C1 | 117.7 (3) |
C4—C3—H3A | 111.2 | C10—C11—H11A | 109.5 |
C2—C3—H3A | 111.2 | C10—C11—H11B | 109.5 |
C4—C3—H3B | 111.2 | H11A—C11—H11B | 109.5 |
C2—C3—H3B | 111.2 | C10—C11—H11C | 109.5 |
H3A—C3—H3B | 109.1 | H11A—C11—H11C | 109.5 |
C9—C4—C3 | 121.8 (3) | H11B—C11—H11C | 109.5 |
C9—C4—C5 | 109.2 (3) | C14—C12—C13 | 109.7 (3) |
C3—C4—C5 | 102.5 (2) | C14—C12—C6 | 113.3 (3) |
C9—C4—H4 | 107.5 | C13—C12—C6 | 114.6 (3) |
C3—C4—H4 | 107.5 | C14—C12—H12 | 106.2 |
C5—C4—H4 | 107.5 | C13—C12—H12 | 106.2 |
C1—C5—C6 | 118.0 (2) | C6—C12—H12 | 106.2 |
C1—C5—C4 | 103.8 (2) | C12—C13—H13A | 109.5 |
C6—C5—C4 | 112.5 (2) | C12—C13—H13B | 109.5 |
C1—C5—H5 | 107.3 | H13A—C13—H13B | 109.5 |
C6—C5—H5 | 107.3 | C12—C13—H13C | 109.5 |
C4—C5—H5 | 107.3 | H13A—C13—H13C | 109.5 |
C7—C6—C5 | 107.3 (2) | H13B—C13—H13C | 109.5 |
C7—C6—C12 | 115.3 (3) | C12—C14—H14A | 109.5 |
C5—C6—C12 | 113.1 (2) | C12—C14—H14B | 109.5 |
C7—C6—H6 | 106.9 | H14A—C14—H14B | 109.5 |
C5—C6—H6 | 106.9 | C12—C14—H14C | 109.5 |
C12—C6—H6 | 106.9 | H14A—C14—H14C | 109.5 |
O1—C7—C6 | 113.9 (2) | H14B—C14—H14C | 109.5 |
O1—C7—C8 | 109.0 (2) | C9—C15—H15A | 120.0 |
C6—C7—C8 | 112.9 (3) | C9—C15—H15B | 120.0 |
O1—C7—H7 | 106.8 | H15A—C15—H15B | 120.0 |
C10—C1—C2—C3 | −116.4 (3) | C5—C6—C7—C8 | 52.9 (3) |
C5—C1—C2—C3 | 6.5 (4) | C12—C6—C7—C8 | 179.9 (3) |
C1—C2—C3—C4 | −31.5 (4) | O1—C7—C8—C9 | −179.9 (3) |
C2—C3—C4—C9 | 166.7 (3) | C6—C7—C8—C9 | −52.2 (4) |
C2—C3—C4—C5 | 44.5 (4) | C7—C8—C9—C15 | −124.2 (4) |
C10—C1—C5—C6 | −95.1 (3) | C7—C8—C9—C4 | 53.1 (4) |
C2—C1—C5—C6 | 145.9 (3) | C3—C4—C9—C15 | 2.1 (6) |
C10—C1—C5—C4 | 139.6 (3) | C5—C4—C9—C15 | 121.1 (4) |
C2—C1—C5—C4 | 20.5 (3) | C3—C4—C9—C8 | −175.3 (3) |
C9—C4—C5—C1 | −170.9 (3) | C5—C4—C9—C8 | −56.3 (4) |
C3—C4—C5—C1 | −40.5 (3) | C5—C1—C10—O2 | −31.7 (5) |
C9—C4—C5—C6 | 60.4 (3) | C2—C1—C10—O2 | 85.3 (4) |
C3—C4—C5—C6 | −169.2 (3) | C5—C1—C10—C11 | 150.5 (3) |
C1—C5—C6—C7 | −179.0 (3) | C2—C1—C10—C11 | −92.5 (4) |
C4—C5—C6—C7 | −58.0 (3) | C7—C6—C12—C14 | −53.3 (4) |
C1—C5—C6—C12 | 52.8 (3) | C5—C6—C12—C14 | 70.7 (4) |
C4—C5—C6—C12 | 173.7 (3) | C7—C6—C12—C13 | 73.6 (4) |
C5—C6—C7—O1 | 178.0 (2) | C5—C6—C12—C13 | −162.4 (3) |
C12—C6—C7—O1 | −55.0 (3) |
D—H···A | D—H | H···A | D···A | D—H···A |
O1—H1O···O1i | 0.82 | 2.11 | 2.927 (4) | 175 |
C11—H11C···O2ii | 0.96 | 2.53 | 3.430 (6) | 157 |
Symmetry codes: (i) −x+1, y+1/2, −z; (ii) x, y+1, z. |
Acknowledgements
The authors thank Professor Dr Hartmut, FG Strukturforschung, Material-und Geowissenschaften, Technische Universität Darmstadt, Petersenstress 23, 64287 Darmstadt, and Professor Kingston, Department of Chemistry, M/C 0212, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA, for their kind co-operation to measure diffraction data for the title compound and to carry out an antiproliferative bioassay against cancer cell lines.
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