Fast atom bombardment-promoted reductive ring opening of 1,2-benzisothiazoles

Fast atom bombardment mass spectral examination of molecules containing a 1,2-benzisothiazole ring, using a thiol reducing agent matrix, promotes reductive ring opening of the benzisothiazole ring, giving an M+H]⁺ two daltons higher than expected. Measurements using a non-reducing matrix produce the expected M+H]⁺. This is a general phenomenon, observed with a number of molecules containing the benzisothiazole ring. The ring-opened structure has been confirmed by chemical synthesis and observed in metabolic studies.