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The negative-ion fast-atom-bombardment (FAB) mass spectra of procyanidin oligomers are characterized by abundant [M-H]-ions and fragmentation that results primarily from retro-Diels-Alder fission and cleavage of the interflavanoid bond. B/E-linked scanning mass spectrometry established that sequence ions result from unimolecular gas-phase decompositions. A quinone-methide mechanism of interflavanoid bond cleavage is proposed to account for observed ions of different molecular weight originating from isomeric upper and lower flavan units. These ions can be used to establish the sequence of monomer units and also to distinguish a linear from a branched trimer.
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Karchesy et al. (1989) studied this question.
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