Crystal structure of N-deacetyllappaconitine

The title compound, C30H42N2O7 [systematic name: (1S,4S,5S,7S,8S,9S,10S,11S,13R,14S,16S,17R)-20-ethyl-4,8,9-trihydroxy-1,14,16-trimethoxyaconitan-4-yl 2-aminobenzoate], isolated from roots of Aconitum sinomontanum Nakai, is a typical aconitane-type C19-diterpenoid alkaloid, which crystallizes with two independent molecules in the asymmetric unit. The conformations of the two independent molecules are closely similar. Each molecule comprises four six-membered rings (A, B, D and E) including one six-membered N-containing heterocyclic ring (E), and two five-membered rings (C and F). Rings A, B and E adopt chair conformations, while ring D displays a boat conformation. Five-membered rings C and F exhibit envelope conformations. IntramolecularN—H⋯O hydrogen bonds between the amino group and carbonyl O atom help to stabilize molecular structure. In the crystal, O—H⋯O hydrogen bonds link the molecules into zigzag chains propagating in [010].


S1. Comment
The title compound, N-deacetyllappaconitine, is produced by several species of the plant genus Aconitum (A. sinomontanum, A. barbatum, A. septentrionale, A. leucostomum, A. orientale) and its structure was confirmed by the NMR and MS data. It possesses antiarrhythmic, analgesic, local anesthetic, sedative and anti-inflammatory activity (Peng et al. 2000;Wang et al. 2009Wang et al. , 2010Romanov et al. 2008). Herewith we present the crystal structure of N-deacetyllappaconitine (I).
The title compound (I) crystallizes with two independent molecules in the asymmetric unit ( Fig. 1).

S2. Experimental
The title compound was isolated from the roots of Aconitum sinomontanum Nakai following the known procedure (Peng et al., 2000). Colourless single crystals suitable for X-ray diffraction were obtained by slow evaporation from a methanol solution for two weeks at the room temperacture.

S3. Refinement
The hydrogen atoms were placed in calculated positions and refined as riding with U iso (H) =1.2-1.5 U eq (C, O). The positions of methyl and hydroxy hydrogens were rotationally optimized. In spite of acceptable value of Flack parameter of -0.07 (15) in the abscence of anomalous scatterers, the absolute configuration of the title compound has been assigned to be the same as that reported for typical natural aconitane-type C 19 -diterpenoid alkaloids (Wang et al., 2007;He et al., 2008).

Figure 1
Two independent molecules in the asymmetric unit showing the atomic labeling and 30% probabilty displacement ellipsoids. H atoms omitted for clarity.

Figure 2
The overlay of two independent molecules.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 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.