Fast-atom bombardment mass spectrometric studies of trisubstituted 3a,4,5,11-tetrahydro-1,2,4-oxadiazolo[5,4-d][1,5]benzothiazepines

The fragmentation pathways of nineteen 1,3a,5-trisubstituted 3a,4,5,11-tetr ahydro-1,2, 4-oxadiazolo[5,4-d][1,5]benzothiazepines have been studied with the aid of mass-analyzed ion kinetic energy spectrometry and exact mass me asurements using fast-atom bombardment ionization, All compounds show a ten dency to eliminate a neutral propene, or substituted or unsubstituted styre ne, from the thiazepine ring to yield 1,2,4-oxadiazolo[5,4-b][1,3]benzothia zole ions, and further undergo reverse 1,3 dipolar cycloadditions to give b enzothiazole ions. The formation of stable conjugated fused tetracyclic sys tems, substituted 1,2, 4-oxadiazolo[5,4-f]phenanthridine ions, was also obs erved. Copyright (C), 1999 John Wiley & Sons, Ltd.