STUDIES ON ALKALOIDS OF ACONITUM EPISCOPALE LE'VL

Four new diterpenoid alkaloids, episcopalisine, episcopalisinine, episcopalitine and episcopalidine were isolated from the root of Aconitum episcopale Le'vl native to China. On the basis of their IR, UV, MS, ¹H NMR, ¹³C NMR spectra and chemical derivatization, the structures of the first three alkaloids has been elucidated (3,4,5) and the structure of episcopalidine has been postulated (8). Recently, according to the result of X-ray diffraction study the structure- of episcopalidine. should be revised as (9).Consideration of structural features seem to justify the classification of the C₁₈diterpenoid alkaloids as a separate group and not as a 4-nor subgroup under the C₁₉-diterpenoid alkaloids. In these alkaloids the C-3(in most) and C-6 positions are not oxygenated. According to the substitution pattern at C-4 they can be further subdivided into two types: one possessing oxygenated groups. (e. g., ester, hydroxyl or epoxy) and the other possessing none. In the ¹H NMR spectra of C₁₈-diterpenoid alkaloids a multiplet of four protons at 1.1～1.6 ppm was due to C-3 and C-6 methylenes. The mass spectra of some C₁₈-diterpenoid alkaloids containing ester groups at C-4, for example ranaconitine and lappaconitine, display base peaks corresponding to the loss Of the acidic moiety from the molecular ion⁽¹⁶⁾, the carboxylic hydrogen being furnished by C-5. This is different from C₁₉-diterpenoid alkaloids, where the base peak corresponds to loss of OR from C-1.