Studies on the stability of diester-diterpenoid alkaloids from the genus Aconitum L. by high performance liquid chromatography combined with electrospray ionisation tandem mass spectrometry (HPLC/ESI/MSn).

The stability of diester-diterpenoid alkaloids (DDA) from plants of the genus Aconitum L. has been studied in different solvents and pH buffers. The HPLC/ESIMS method for analysing the concentration of DDA was established and DDA's decomposition products were elucidated by HPLC/ESI-MS/MS(n). In different solvents, e.g. dichloromethane, ether, methanol and distilled water, the decomposition pathways of DDA are quite different and their difference in stabilities depends on the difference of their structures, in which substituents at the N atom and substituents at C-3 are different. The pyrolytic products of DDA, such as deacetoxy aconitine-type alkaloids, have been observed in the above solvents, whereas 8-methoxy-14-benzoyl aconitine-type alkaloids have been obtained only in methanol. Furthermore, the experimental results demonstrate that the stability of DDA depends on pH values of the buffer. Aconine as hydrolysate has been only found in pH 10.0 buffer, and the other hydrolysates and the pyrolyzates of DDA, such as benzoylaconine and deacetoxy aconitine, have been observed in all pH aqueous solutions. The decomposition pathways of DDA in buffers are related to the substituent on the C-3 position. The decomposition pathway of aconitine is similar to that of mesaconitine, but different from that of hypaconitine. Copyright 2007 John Wiley & Sons, Ltd.