9α-Acetoxy-1β,10α-epoxyparthenolide

The title compound, C17H22O6, was semi-synthesized from 9-hydroxyarthenolide, which was isolated from the chloroform extract of the aerial parts of Anvillea radiata. The molecule contains fused five- and ten-membered rings: the five-membered lactone ring has a twisted conformation, whereas the ten-membered ring displays an approximate chair–chair conformation. The dihedral angle between the rings is 24.76 (9)°.

The title compound, C 17 H 22 O 6 , was semi-synthesized from 9hydroxyarthenolide, which was isolated from the chloroform extract of the aerial parts of Anvillea radiata. The molecule contains fused five-and ten-membered rings: the fivemembered lactone ring has a twisted conformation, whereas the ten-membered ring displays an approximate chair-chair conformation. The dihedral angle between the rings is 24.76 (9) .

Comment
The Natural sesquiterpene lactone (9α-hydroxyparthenolide) is the main constituent of the chloroform extract of aerial parts of Anvillea radiata (El Hassany et al., 2004), and of Anvillea garcini (Abdel Sattar et al.,1996). The reactivity of this sesuiterpène and its derivatives has been the subject of several studies (Castaneda-Acosta et al.,1993;Neukirch et al., 2003), in order to prepare products with high value added, used in industrial pharmacology. In the same context, we carried out the acetylation followed by epoxydation of 9α-hydroxyparthenolide. Thus, the action of one equivalent of acetic anhydride on this sesquiterpene in pyridine at 0°C leads to quantitative yield 9α-acétoxyparthenolide. The treatment of this latter with one equivalent of meta-choroperbenzoïque acid (mCPBA) in dichloromethane at room temperature gives 9α-acetoxy-1β, 10β-epoxyparthenolide with a yield of 95%. The structure of this new product was determined by NMR spectral analysis of 1H, 13 C and mass spectrometry, and confirmed by a study of X ray crystallography. The structure of (I) was established by 1H and 13 C NMR and confirmed by its single-crystal X-ray structure.The molecule is built up from two fused five-and ten-membered rings. (Fig. 1). The five-membered ring adopts a twisted conformation,as indicated by Cremer & Pople (1975) puckering parameters Q = 0.26 (2) Å and φ = 23.77 (4)°. The ten-membered ring displays an approximate chair-chair conformation. This is the typical conformation observed for other sesquiterpenes lactones (Moumou et al., 2010;Watson & Zabel, 1982;Castaneda-Acosta et al., 1997).

Experimental
To a solution of 1,2 g (4,54 mmol) of 9α-hydroxyparthenolide in 30 ml of pyridine was added 10 ml of acetic anhydride.
The mixture is left stirring for 12 h at room temperature and then treated with 100 ml of ice water and extracted with chloroform. The residue obtained after drying and evaporation of solvent was chromatographed on silica gel eluting with hexane-ethyl acetate (80/20) and allowed to isolate in pure form with a yield qantitatif the 9α-acétoxyparthenolide. To 0.5 g (1,6 mmol) of this latter dissolved in 40 ml of dichloromethane is added an equivalent of acid meta chloroperbenzoïque (mCPBA). The reaction mixture was stirred at room temperature for 3 h, then treated with a solution of sodium bisulfite at 10% and extracted with dichloromethane. The organic phase is dried over sodium sulfate and then evaporated under vacuum. chromatography of the residue obtained on silica gel column eluting with hexane ethyl acetate (75/25), allowed us to obtain the 9α-Acetoxy-1β, 10α-epoxyparthenolide with a yield of 80%.Crystallization of this product was carried out at room temperature from an ethyl acetate solution.

Refinement
All H atoms were fixed geometrically and treated as riding with C-H = 0.96 Å (methyl),0.97 Å (methylene), 0.98Å (methine) with U iso (H) = 1.2Ueq(methylene, methine and OH) or U iso (H) = 1.5Ueq(methyl). In the absence of significant anomalous scattering, the absolute configuration could not be reliably determined and thus 2417 Friedel pairs were merged and any references to the Flack parameter were removed.