<p>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-MS<sup>n</sup>) 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 C<sub>2</sub>H<sub>3</sub>O<sub>2</sub>•
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‒CH<sub>3</sub>OH]<sup>‒</sup> 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‒CH<sub>3</sub>OH]<sup>‒</sup> 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). </p>