Gas-phase fragmentation of gamma-lactone derivatives by electrospray ionization tandem mass spectrometry.

Fragmentation reactions of beta-hydroxymethyl-, beta-acetoxymethyl- and beta-benzyloxymethyl-butenolides and the corresponding gamma-butyrolactones were investigated by electrospray ionization tandem mass spectrometry (ESI-MS/MS) using collision-induced dissociation (CID). This study revealed that loss of H(2)O [M+H-8](+) is the main fragmentation process for beta-hydroxymethylbutenolide (1) and beta-hydroxymethyl-gamma-butyrolactone (2). Loss of ketene ([M+H-42](+)) is the major fragmentation process for protonated beta-acetoxymethyl-gamma-butyrolactone (4), but not for beta-acetoxymethylbutenolide (3). The benzyl cation (m/z 91) is the major ion in the ESI-MS/MS spectra of beta-benzyloxymethylbutenolide (5) and beta-benzyloxymethyl-gamma-butyrolactone (6). The different side chain at the beta-position and the double bond presence afforded some product ions that can be important for the structural identification of each compound. The energetic aspects involved in the protonation and gas-phase fragmentation processes were interpreted on the basis of thermochemical data obtained by computational quantum chemistry.