Trimethylsilyl group migration in the mass spectra of trimethylsilyl ethers of cholesterol oxidation products. product ion characterization by linked-scan tandem mass spectrometry

Abstract

Loss of the A ring in the electron-impact mass spectra of the trimethylsilyl (TMS) derivatives of several cholesterol oxidation products is accompanied by intramolecular migration of the 3-O-TMS group to the charge-retaining portion of the molecule. Linked-scan techniques (B/E and B(2)/E) were used to establish the fragmentation processes leading to the formation of the rearrangement ion. The TMS group appears to migrate to heteroatomic sites in the 5-; 6-, or 7-positions of the B ring. This structural assignment is supported by isotopic labeling studies and collision-induced dissociation of the resulting product ion.