Electron ionization fragmentation mechanisms of different substituted 2,3-dihydro- and 2,3,4,5-tetrahydro-1,5-benzothiazepines

The electron ionization induced fragmentations of ten biologically significant 2,3-dihydro-1,5-benzothiazepines and the corresponding 2,3,4,5-tetrahydro-1,5-benzothiazepines have been studied by low- and high-resolution mass spectrometry. The fragmentations follow a general pattern, the details of which are discussed with respect to the nature and position of the substituent in the aromatic ring. The dihydro- and tetrahydro-1,5-benzothiazepines both undergo fragmentation through four routes (A-D). However, the most significant fragmentation takes place through route A, leading to the elimination of ring A or ring B of the molecule. The difference between the fragmentation patterns of dihydro- and tetrahydro-1,5-benzothiazepines appears mainly in route E where a phenylallylhydroxybenzene cation appears in all tetrahydro-1,5-benzothiazepines but is not observed in the corresponding dihydro derivatives.