Mechanism of formation of doubly charged fragments from bis‐benzyltetrahydroisoquinolines under electron impact

Abstract

Some bis-benzyltetrahydroisoqnholhes [ol,ol'-di-N,N-(l-benzyl-1,2,3,4-tetr~ydroisoquino~ne)-p-xylene and various substituted analognes] give rke to very abundant doubly charged fragment ions under electron impact, corresponding to the loss of the two benzyl groups. Substituent effects, ionization and appearance energy measurements and metastable transitions show that these doubly charged ions are formed (at least in part) from singly charged precursors by a heterolytic cleavage (charge separation).

API-ionspray MS and MS/MS study on the structural characterization of bisbenzylisoquinoline alkaloids

“…6), showed as prominent as well as intense in API-ionspray MS/MS, but revealed less abundant in EI-MS and FAB-MS These fragment ions corresponding to ethereal ring E and ring F via dibenzylic cleavages of the dimeric alkaloids, such as product ion at m/z 213 (g) via obamegine, oxyacathine and thalicberine, product ion at m/z 227 (h) via thalrugosine, isotetrandrine, obaberine, O-methylthalicberine, northalrugosine, thalrugosidine and thalidasine, and product ion at m/z 243 (w) via thalibrunine, were less abundant in the MS/MS data of all investigated alkaloids due to less ionic characteristics of these ions (Fig. 6), however, these diphenyl ether ions did not reveal in EI-MS, CI-MS and FAB-MS [1,2,4,[6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. API-ionspray MS and MS/MS analysis of the investigated alkaloids exhibited more sensitivity of detection in Q1 scan MS and more fragment as well as intense product ions in MS/MS in nanogram quantities than those of CI-MS, EI-MS and FAB-MS in more than 10 g quantities.…”

“…Previously, structural elucidation of these natural products have mainly relied on EI-MS, CI-MS and FAB-MS, however, these techniques are not sensitive, and need more than 10 g of material [4,[6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. Early EI-MS and FAB-MS studies displayed low abundances of molecular/adduct molecular ions and fragment ions for these alkaloids [4,[6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. CI-MS showed intense protonated molecular ions for these secondary and tertiary alkaloids with very less fragment ions for the structural information of the secondary and tertiary alkaloids, and no molecular ions detected for the quaternary alkaloids [4,[6][7][8][9][10][11][12][13][14]…”

“…Early EI-MS and FAB-MS studies displayed low abundances of molecular/adduct molecular ions and fragment ions for these alkaloids [4,[6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. CI-MS showed intense protonated molecular ions for these secondary and tertiary alkaloids with very less fragment ions for the structural information of the secondary and tertiary alkaloids, and no molecular ions detected for the quaternary alkaloids [4,[6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. We have reported previously preliminary results for the structural fragments from these 20 monoether and diether links of bisbenzylisoquinoline alkaloids using API-ionspray MS and MS/MS techniques [23].…”