3-Deoxyaconitine from the root of Aconitum Carmichaeli Debx.

The title compound (systematic name: 8β-acetoxy-14α-benzoyloxy-N-ethyl-13β,15α-dihydroxy-1α,6α,16β-trimethoxy-4β-methoxymethyleneaconitane), C34H47NO10, is a typical aconitine-type C19-diterpenoid alkaloid, and was isolated from the roots of the Aconitum carmichaeli Debx. The molecule has an aconitine carbon skeleton with four six-membered rings and two five-membered rings, whose geometry is similar to these observed in other C19-diterpenoid alkaloids; both of five-membered rings have the envelope configurations and the six-membered N-containing heterocyclic ring displays a chair conformation. Intramolecular O—H⋯O hydrogen bonding occurs. Weak intermolecular C—H⋯O hydrogen bonding is observed in the crystal structure.

The title compound (systematic name: 8-acetoxy-14-benzoyloxy-N-ethyl-13,15-dihydroxy-1,6,16-trimethoxy-4methoxymethyleneaconitane), C 34 H 47 NO 10 , is a typical aconitine-type C 19 -diterpenoid alkaloid, and was isolated from the roots of the Aconitum carmichaeli Debx. The molecule has an aconitine carbon skeleton with four six-membered rings and two five-membered rings, whose geometry is similar to these observed in other C 19 -diterpenoid alkaloids; both of fivemembered rings have the envelope configurations and the sixmembered N-containing heterocyclic ring displays a chair conformation. Intramolecular O-HÁ Á ÁO hydrogen bonding occurs. Weak intermolecular C-HÁ Á ÁO hydrogen bonding is observed in the crystal structure.

Experimental
Air-dried and powdered roots (400 g) were percolated with 0.1 M HCl solution (5 L). The obtained acid aqueous solution was basified with 10% aqueous NH 4 OH to pH 10 and then extracted with ethyl acetate (6 L×3). Removal of the solvent under reduced pressure afforded the total crude alkaloids (2.0 g) as a yellowish amorphous powder, which was chromatographed over a silica gel column, eluting with cyclohexane-acetone (9:1→1:2) gradient system, to afford deoxyaconitine (180 mg) in cyclohexane-acetone (7:1) gradient system. The crystals suitable for X-ray structure analysis were obtained by slow evaporation from an acetone solution at room temperature.

Refinement
Hydroxy H atoms were located in a difference Fourier map and refined as riding in their as-found relative positions with U iso (H) = 1.5U eq (O). Other H atoms were located geometrically with C-H = 0.93-0.98 Å, and refined using a riding model with U iso (H) = 1.5U eq (C) for methyl and 1.2U eq (C) for the others. The absolute configuration has not been determined from the X-ray analysis, owing to the absence of strong anomalous scattering, and Friedel's pairs were merged. Bond distance restraints for three bonds were applied. Fig. 1. The molecular structure of the title compound with 30% probability displacement ellipsoids for non-H atoms. H atoms not including in hydrogen bonding have been omitted for clarity.

Special details
Experimental. The absolute structure of the title compound can not be determined by the X-ray analysis, owing to the absence of strong anomalous scatterers. But it can be deduced by the comparision to the known diterpenoid alkaloids, for the unique absolute configuration of the similar natural products.
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 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 > σ(F 2 ) is used only for calculating Rfactors(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.