Gas-phase fragmentation reactions of protonated benzofuran- and dihydrobenzofuran-type neolignans investigated by accurate-mass electrospray ionization tandem mass spectrometry

We have investigated gas-phase fragmentation reactions of protonated benzofuran neolignans (BNs) and dihydrobenzofuran neolignans (DBNs) by accurate-mass electrospray ionization tandem and multiple-stage (MSn) mass spectrometry combined with thermochemical data estimated by Computational Chemistry. Most of the protonated compounds fragment into product ions B ([M + H-MeOH](+)), C ([B-MeOH](+)), D ([C-CO](+)), and E ([D-CO](+)) upon collision-induced dissociation (CID). However, we identified a series of diagnostic ions and associated them with specific structural features. In the case of compounds displaying an acetoxy group at C-4, product ion C produces diagnostic ions K ([C-C2H2O](+)), L ([K-CO](+)), and P ([L-CO](+)). Formation of product ions H ([D-H2O](+)) and M ([H-CO](+)) is associated with the hydroxyl group at C-3 and C-3 ', whereas product ions N ([D-MeOH](+)) and O ([N-MeOH](+)) indicate a methoxyl group at the same positions. Finally, product ions F ([A-C2H2O](+)), Q ([A-C3H6O2](+)), I ([A-C6H6O](+)), and J ([I-MeOH](+)) for DBNs and product ion G ([B-C2H2O](+)) for BNs diagnose a saturated bond between C-7 ' and C-8 '. We used these structure-fragmentation relationships in combination with deuterium exchange experiments, MSn data, and Computational Chemistry to elucidate the gas-phase fragmentation pathways of these compounds. These results could help to elucidate DBN and BN metabolites in in vivo and in vitro studies on the basis of electrospray ionization ESI-CID-MS/MS data only.