Should We Think Positive or Negative About Dihydrobenzofuran Neolignans? an ESI-MS/MS Study

This study elucidates the gas-phase fragmentation pathways of a series of biologically active benzofuran neolignans (BNs) and dihydrobenzofuran neolignans (DBNs) by means of electrospray ionization accurate-mass tandem and sequential mass spectrometry (ESI-MS/MS and ESI-MSn) and thermochemical data estimated by using Computational Chemistry and the B3LYP/6-31+G(d,p) model. In their deprotonated forms, these compounds produced more diagnostic product ions as compared to the corresponding protonated molecules. Moreover, a series of odd-electron product ions (radical anions) were detected, which has not been reported for protonated DBNs. Direct C2H3O2• elimination from the precursor ion (deprotonated molecule) only occurred for the BNs and can help to distinguish these compounds from the DBNs. Although the product ion [M‒CH3OH]‒ emerged in the spectrum of all the DBNs analyzed here, the mechanism through which this ion originates strongly depends on specific structural features, so that further [M‒CH3OH]‒ fragmentation generates important diagnostic product ions. Comparison between the ESI-MS/MS data of these compounds in the negative ion mode (deprotonated molecule) and in the positive ion mode (protonated molecule) revealed that the negative ion mode provides much more information (at least one diagnostic product ion emerged for all the analyzed compounds) and does not require the use of additives to produce the precursor ions (deprotonated molecules).