The mass spectral analysis of isolated hops A-type proanthocyanidins by electrospray ionization tandem mass spectrometry.
Comprehensive mass spectral fragmentation patterns have been established for sequencing chromatographically isolated A-type proanthocyanidins (PAs) using electrospray ionization tandem mass spectrometry (ESI-MS(n)) in the positive ion mode similar to those used for sequencing previously reported B-type PAs. Sequence-identifying fragmentations for A-type PAs include heterocyclic ring fission (HRF), retro-Diels-Alder (RDA) fission, benzofuran-forming (BFF) fission, and quinone methide (QM) fission. There is commonality in fragmentation patterns between A-type and B-type PAs, but distinguishing features in the mass spectral patterns between the two classes include 2-Da mass differences in the pseudo molecular ions, the propensity for the A-type PAs to undergo QM fissions and yield bis-quinoid ions as opposed to mono-quinoid ions in the upper unit of the sequence, and the reluctance of A-type linkages to undergo RDA, BFF, and BFF/H(2)O fissions from the upper unit. The positions of one or more A-type (C2-->O-->C7') ether linkages have been located in sequences of PAs ranging in chain lengths of two to five monomer units using ESI-MS(n) data. Using the fragmentation information from ESI-MS(n) experiments, a total of 17 PAs were structurally sequenced by systematic real time ESI-MS(n). Among them ten A-type and six B-type hop PAs are reported here for the first time.
Li
Hui-Jing
HJ
Department of Chemistry, Oregon State University, Corvallis, OR 97331-4003, USA.
Deinzer
Max L
ML
D002851:Chromatography, High Pressure Liquid; D027582:Humulus / Q000737:chemistry*; D007202:Indicators and Reagents; D044945:Proanthocyanidins / Q000032:analysis*; D021241:Spectrometry, Mass, Electrospray Ionization; D013056:Spectrophotometry, Ultraviolet; D053719:Tandem Mass Spectrometry
D007202:Indicators and Reagents; D044945:Proanthocyanidins