MASS SPECTROMETRIC STUDY ON EPISCOPALIDINE AND ITS ANALOGUES

This paper reports the mass spectral characteristics of episcopalidine and its analogues (1～15). The features of its fragmentation under electron impact are as follows:1. The substituent groups, especially the ester group, of episcopalidine and its analogues affect significantly the relative abundance of the molecular ion peaks. In general, compounds with the ester group (such as 1, 3, 5)exhibited weak molecular ion peaks, and the alkamine (such as 2, 8) fairly strong ones.In the high mass range, characteristic peaks, such as M-17, M-18, M-28, M-43, M-59, M-60 and M-121, showing losses of substituent groups were observed. The oxygenated groups at C-3 and C-2 always give rise to even mass intense ion peaks(M-OR³) followed by elimination of the oxygenated groups at C-2(M-OR³-HOR²).3. In the middle mass range, characteristic ion peaks of songorine-type fragmentation of ring A (the loss of C-1—C-3), m/z 282(254, 122) (1～8), m/z 284(256, 122) (9～10), m/z 286(258, 122) (12, 13), may be discerned. It is of interest to note that in the mass spectrum of hetidine another fragmentation of ring A (the loss of C-2—C-3) also may be observed. The present study shows: veatchine-type(such as songoramine), denudatine-type(such as 15-acetyldenudatine), hetidine-type(such as 1～13) and some carbinolamine ether-containing (such as gadensine) diterpvnoid alkaloids give rise to the ring A fragmentation of songorine-type. This fragmentation is absent in hetisine-type and non-carbinolamine ether-containing C₁₈, C₁₉, and lactone-type diterpenoid alkaloids. However, the failure of compounds 14 and 15 to show this fragmentation is possibly a result of some structural peculiarities. Similar extrusions of fragments (except the carbonyl group) from other rings are also detectable.The fragmentation mechanisms were based on high resolution data and metastable measurements and may prove useful in structural elucidation of unkown alkaloids of the same types.