Crystal structure of tuguaconitine,a diterpene alkaloid from Aconitum sibiricum

The three-dimensional structure of a natural product, tuguaconitine (C23H35NO7) from Aconitumrn sibiricum was determined by single crystal X-ray diffraction analysis. The compound was recrystallized from a methanol solution into orthorhombic crystal system, with a = 18.093(4), b = 12.075(11), c = 9.824(4) A, Dm = 1.35, Dx= 1.354 g/cm3, space group P2(1)2(1)2(1), and Z=4. The structure was solved by direct method and refined by least-squares procedure to the final R value of 0.046 for 1495 observed reflections with I > or = 2sigma(I). Aconitines are diterpene alkaloid composed of six rings. In the molecule, two 6-membered rings have stable chair conformation, but other two 6-membered rings have unstable boat conformation because of their bonding strain and hydrogen bonds. Based on the three-dimensional structure of tuguaconitine, we suggest another 2D-diagram for the compound which is far better in imagination of the spatial shape of the molecule than the ordinary one.