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-tetrahydro- 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 measurements using fast-atom bombardment ionization. All compounds show a tendency to eliminate a neutral propene, or substituted or unsubstituted styrene, from the thiazepine ring to yield 1,2,4-oxadiazolo[5,4-b][1,3]benzothiazole ions, and further undergo reverse 1,3-dipolar cycloadditions to give benzothiazole ions. The formation of stable conjugated fused tetracyclic systems, substituted 1,2,4-oxadiazolo[5,4-f]phenanthridine ions, was also observed. Copyright © 1999 John Wiley & Sons, Ltd.