Mesaconitine

The title compound, (1α,3α,6α,14α,15α,16β)-3,8,13,14,15-pentahydroxy-1,6,16-trimethoxy-4-methoxymethyl-20-methylaconitan-8,14-diyl 8-acetate 14-benzoate, C33H45NO11, a C19 diterpenoid alkaloid, obtained from the roots of Aconitum kusnezoffii, has been crystallographically characterized in this study. Rings A, B and E have chair conformations, rings C and F display envelope conformations, and ring D adopts a boat conformation. There are inter- and intramolecular O—H⋯O hydrogen bonds, the latter resulting in the formation of a non-planar seven-membered ring. The intermolecular interactions link the molecules into a two-dimensional network.

of most biologically active molecules plays a role in governing their interactions and activities. It is important to obtain information on the mode of action and selectivity of mesaconitine so that it can be used safely and efficiently. Many X-ray crystal structure determinations of C 19 diterpenoid alkaloids have been reported, such as pseudaconitine, delphinine (Parvez et al., 1999;Pelletier et al., 1982.). However, the crystal structure of mesaconitine has not been reported. In view of this, the crystal structure determination of the title compound was carried out and the results are presented here.
The structure of mesaconitine is similar to that of aconitine (Codding, 1982). The only difference between aconitine and mesaconitine is a methylene group at the tertiary nitrogen atom. The bond lengths and angles in the title compound are in good agreement with expected values. In the molecule of the title compound, (Fig. 1), rings A, B and E have a chair conformation, rings C and F display an envelope conformation, ring D adopts a boat conformation. The packing of the title compound is shown in Fig. 2. In the crystal structure, there are inter-and intramolecular O-H···O hydrogen bonds.
The former link the molecules into a two-dimensional network, while the latter results in the formation of a non-planar seven-membered ring. These intramolecular hydrogen bonds may be effective in the stabilization of the structure.

Experimental
The title compound was isolated from the roots of A. kusnezoffii according to the literature procedure of Li et al. (1997) and crystals of X-ray quality were grown from methanol at room temperature by slow evaporation.

Refinement
The H atom attached to C2 was located and refined freely [C-H = 0.97 (2) Å]. Other H atoms were included in the refinement at idealized positions and refin ed as riding, with C-H = 0.95 (aromatic), 0.98 (CH 2 ), 1.00 (CH), O-H = 0.84 Å. U iso (H) = xU eq (carrier atom), where x = 1.5 for O and methyl, 1.2 for all other H atoms. In the absence of significant anomalous scattering effects, Friedel pairs were merged. The absolute configuration was assigned on the basis of the related literature (Pelletier & Djarmati, 1976;Tsuda & Marion, 1963;Zhapova et al., 1986). Fig. 1. A view of the structure of the title compound, showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. H atoms have been omitted for clarity.  3,8,13,14,15-pentahydroxy-1α,3α,6α,14α,15α,16β-20-methyl-1,6,16-trimethoxy-4-methoxymethylaconitan-8,14-diyl   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.