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.