Although procyanidins constitute a unique class of polymeric plant secondary metabolites with a variety of biological properties including potent antioxidant activity, structure determination has been challenging, and structures of many complex procyanidins remain uncertain. To expedite the characterization of procyanidins, negative ion matrix-assisted laser desorption ionization high-energy collision-induced dissociation tandem time-of-flight (MALDI-ToF/ToF) mass spectra of 20 isolated procyanidins containing catechin and epicatechin subunits with degrees of polymerization up to five were obtained and evaluated. Structurally significant fragmentation pathways of singly charged, deprotonated molecules were identified representing quinone methide, heterocyclic ring fission, and retro-Diels-Alder fragmentation. The interpretation of the tandem mass spectra for sequencing A-type, B-type, mixed-type, linear, and branched procyanidins is explained using specific examples of each.
Keywords: MALDI; fragmentation; mass spectrometry; procyanidin.