Euphorbia factor L8: a diterpenoid from the seeds of Euphorbia lathyris

The title compound [systematic name: (2S*,3S*,4R*,5R*,9S*,11S*,15R*)-5,15-diacetoxy-3-nicotinoyloxy-14-oxolathyra-6(17),12(E)-diene], C30H37NO7, was isolated from the seeds of Euphorbia lathyris. The tricyclic diterpenoid molecule contains an 11-membered ring, a five-membered ring exhibiting an envelope conformation and a three-membered ring. The 11-membered ring is cis-fused with the three-membered ring and trans-fused with the five-membered ring.


Experimental
The seeds of E. lathyris (10 kg) were collected in Sichuan province, People's Republic of China and extracted with 95% EtOH at room temperature. The extract was concentrated in vacuo and filtered. The filtrate was partitioned between EtOAc and H 2 O. The EtOAc soluble materials (1 kg) were subjected to silica-gel column chromatography (160-200 mesh, 4 kg) with petrol-EtOAc stepwise elution. The column chromatographic fractions (500 ml each) were combined into 12 fractions according to thin-layer chromatography monitoring analysis. Fraction 5 (7.5 g) was applied to a RP-18 silica-gel column and eluted with MeOH/H 2 O (7:3) to yield five fractions. Fraction 5.2 (1.4 g) was subjected to silica-gel column chromatography (200-300 mesh, 50 g) and eluted with petrol-EtOAc (5:1) to afford the compound (I). The isolated product was recrystallized at room temperature from acetone to afford the block crytals. 13

Refinement
All hydrogen atoms were located geometrically with C-H distances of 0.93-0.98 Å, and refined using a riding model.
The absolute configuration could not be determined from the X-ray analysis, owing to the absence of strong anomalous scatterers, and Friedel pairs were averaged. However, the absolute configuration can be suggested on a biogenetic basis (Appendino et al., 1999).

Data collection
Enraf-Nonius CAD-4 diffractometer R int = 0.003 Radiation source: fine-focus sealed tube θ max = 25.5º Monochromator: graphite θ min = 1.7º Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 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 (Å 2 )