Mass spectrometry of sterols. Electron ionization induced fragmentation of C-4-alkylated cholesterols.
The electron impact ionization of C-4-alkylated cholest-5-en-3beta-hydroxysterols has been investigated. The mass spectra of the C-4-alkylated cholesterols contain a number of ions in the high mass region for which analogous ions are not found in the spectrum of cholesterol. Detailed studies of the composition and origin of these ions have been made by high resolution mass spectrometry and analysis of metastable ions. In addition, a large number of isotopically (deuterium and 18O) substituted C-4-alkylated analogues have been prepared to assist in the interpretation of the spectra. The combined results indicate the occurrence of a number of very complex and unusual electron ionization induced fragmentations. Most notable of the findings reported herein concerns the demonstration of the formation of an ion involving loss of the elements of ring A with an intramolecular shift of the oxygen and hydrogen atoms of the hydroxyl function to the charge-retaining species.
An unusual mass spectral fragmentation of C-4 alkylated cholesterols
The mass spectra of C-4-alkylated cholest-5-en-3β-hydroxysterols are characterized by an ion (m/e 331) resulting from the unusual intramolecular transfer of the 3β-hydroxy-group to the charge-retaining fragment with concomitant loss of ring A.
High resolution mass spectrometry. Bufadienolides—II.
Complete low resolution mass spectra and some high resolution data are presented and discussed for a series of naturally occurring 14β-hydroxy bufadienolides (toad venoms) and their derivatives, but excluding compounds with a 14β,15β-epoxy group. The bufadienolides employed were bufalin, bufotalin, gamabufotalin, telocinobufagin, arenobufagin, 3β-acetoxybufotalien, 3β-acetoxyhellebrigenin, 3β-acetoxybufalin, 3-ketobufalin, 14-anhydrobufalin, 3β-acetoxy-15-ketobufalin and 15α-hydroxybufalin. The relatively unsaturated 2-pyrone functionality at C-17β has been used as an integral label to distinguish (from elemental composition data) ions containing it, from those coming from other parts of the molecule that do not. Structural ‘ion types’ are proposed to interpret this spectral data, and the prognosis for structure elucidation of other bufadienolides by high resolution mass spectrometry appears good.