Fragmentation of aromatic sulfonamides in electrospray ionization mass spectrometry: elimination of SO2 via rearrangement

Arylsulfonamides are attractive pharmacophores for drug candidates. Fragmentation behaviors of selected aromatic sulfonamides were investigated using electrospray ionization mass spectrometry in the positive ion mode. Some of the sulfonamides afforded unique loss of 64 (loss of SO(2)) ions upon collision-induced dissociation followed by intramolecular rearrangements in the gas phase. This SO(2) elimination-rearrangement pathway leading to the generation of [M + H - SO(2)](+) ions appeared to be susceptible to substitutions on the aromatic (Ar) ring that would affect the Ar--sulfur bond strength and the stability of the partially positive charge developed at the ipso position upon bond dissociation. Electron withdrawing groups such as chlorine attached to the aromatic ring at ortho position seem to promote the SO(2) extrusion. Although this fragmentation pathway in atmospheric pressure ionization MS is less predictable than in electron impact MS, it is a frequently encountered reaction. The absence of this fragmentation pathway in some of the arylsulfonamides indicates that other factors such as nucleophilicity of the nitrogen may also play a role in the process. With respect to the site of attachment of the migrating NR'R'', ipso-substitution on the aromatic ring is evident since this fragmentation mechanism is operative in the fully ortho-substituted arylsulfonamides.