Dehydro­brachylaenolide: an eudesmane-type sesquiterpene lactone

M Rademeyer; F R van Heerden; M M van der Merwe

doi:10.1107/S1600536808042402

. 2008 Dec 24;65(Pt 1):o196. doi: 10.1107/S1600536808042402

Dehydrobrachylaenolide: an eudesmane-type sesquiterpene lactone

M Rademeyer ^a,^*, F R van Heerden ^b, M M van der Merwe ^c

PMCID: PMC2968103 PMID: 21581650

Abstract

The three-ring eudesmanolide, C₁₅H₁₆O₃, is a natural product isolated from Dicoma anomala Sond. (Asteraceae). The compound contains an endo–exo cross conjugated methylenecyclohexenone ring with an envelope conformation trans-fused with cyclohexane and trans-annelated with an α-methylene γ-lactone. The absolute structure was assigned by optical rotation measurements compared to those from the synthetic compound with known stereochemistry. The crystal packing is consolidated by C—H⋯O interactions.

Related literature

For NMR studies of this compound, see: Bohlmann & Zdero, (1982 ▶); Grass et al. (2004 ▶). For the chemical synthesis and confirmation of the absolute structure, see: Higuchi et al. (2003 ▶).

Experimental

Crystal data

C₁₅H₁₆O₃
M _r = 244.28
Orthorhombic,
a = 9.5648 (6) Å
b = 11.1631 (6) Å
c = 11.5542 (6) Å
V = 1233.67 (12) Å³
Z = 4
Mo Kα radiation
μ = 0.09 mm⁻¹
T = 150 (2) K
0.50 × 0.50 × 0.40 mm

Data collection

Oxford Diffraction Excalibur2 CCD diffractometer
Absorption correction: multi-scan (Blessing, 1995 ▶) T _min = 0.909, T _max = 0.963
12604 measured reflections
2294 independent reflections
1988 reflections with I > 2σ(I)
R _int = 0.016

Refinement

R[F ² > 2σ(F ²)] = 0.033
wR(F ²) = 0.095
S = 1.05
2294 reflections
163 parameters
H-atom parameters constrained
Δρ_max = 0.31 e Å⁻³
Δρ_min = −0.21 e Å⁻³

Data collection: CrysAlis CCD (Oxford Diffraction, 2006 ▶); cell refinement: CrysAlis RED (Oxford Diffraction, 2006 ▶); data reduction: CrysAlis RED; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: Mercury (Macrae et al., 2006 ▶); software used to prepare material for publication: PLATON (Spek, 2003 ▶) and WinGX (Farrugia, 1999 ▶).

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536808042402/bi2330sup1.cif

e-65-0o196-sup1.cif^{(18.5KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808042402/bi2330Isup2.hkl

e-65-0o196-Isup2.hkl^{(110.5KB, hkl)}

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

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C6—H6⋯O1ⁱ	0.98	2.39	3.360 (2)	171
C14—H14A⋯O1ⁱ	0.96	2.57	3.393 (2)	143

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Symmetry code: (i) Inline graphic .

Acknowledgments

We thank the National Drug Development Platform (NDDP) and the NRF for funding.

supplementary crystallographic information

Comment

The title compound, a sesquiterpene lactone dehydrobrachylaenolide, was isolated from Dicoma anomala Sond (Asteraceae). These bi-functional exo-endo cross conjugated dienones are of importance as synthetic intermediates in the preparation of biologically active natural products (Higuchi et al., 2003). NMR studies of the compound have been reported previously (Bohlmann & Zdero, 1982; Grass et al., 2004) and the absolute stereochemistry has been confirmed as 3-oxoeudesma-1,4(15),11 (13)-triene-12,6a-olide by chemical synthesis (Higuchi et al., 2003). Here we report the crystal structure. Although the absolute structure could not be elucidated by X-ray diffraction, unambiguous assignment of stereochemistry was made on the basis of the value of optical rotation ([α] ²⁴_D+68° (c 1/2, CHCl₃)) which is identical to that of the synthetic compound ([α] ²⁴_D+67.9° (c 0.16, CHCl₃)) for which the stereochemistry is known (Higuchi et al., 2003) and very close to the value for the naturally isolated material ([α]²⁴_D+67° (c 0.16, CHCl₃)) (Bohlmann & Zdero, 1982).

The molecular geometry and labelling scheme are shown in Fig. 1. The methylenecyclohexenone ring adopts an envelope conformation, with the C5 atom out of the plane of the ring by approximately 0.7 Å. The γ-lactone ring is twisted on C6—C7, while the cyclohexane ring adopts a chair conformation. An axial position is occupied by methyl group C14, and the methylene carbon atom C15 is in the equatorial position. A weak intramolecular interaction is formed between C15—H15B···O2. Fig. 2 illustrates the molecular packing viewed down the c axis. Weak intermolecular hydrogen bonds are present between atoms C6—H6···O1ⁱ and and C14—H14···O1ⁱ [symmetry code (i): 1/2 - x, 1 - y, 1/2 + z].

Experimental

The compound was isolated from Dicoma anomala Sond (Asteraceae), and recrystallized from propanol at room temperature.