Abstract:

A series of six matrine-type alkaloids, including a pair of stereoisomers, was investigated using electrospray ionization quadrupole time-of-flight tandem mass spectrometry (ESI-QTOF-MS/MS) in positive-ion mode. Protonated molecules were fragmented by collision-induced dissociation (CID) and the products identified. The identity of the major product ions was also supported by deuterium-labeling experiments. It was found that sequential four-centered H rearrangements play a significant role in the fragmentation of the piperidine-ring; the RDA reaction dominates the dissociations for sophocarpine and sophocarpidine; and the McLafferty-type rearrangement occurs with neosophoramine. Interestingly, a pair of stereoisomers matrine and sophoridine, can be unambiguously distinguished using CID, and this characterization was supported by the DFT calculations of the potential energy profiles for protonated matrine and sophoridine before dissociation to the product ion at m/z 152.