Journal
PHYTOCHEMICAL ANALYSIS
Volume 18, Issue 3, Pages 193-203Publisher
WILEY
DOI: 10.1002/pca.967
Keywords
MALDI-TOF/MS; ESI/MS; C-13-NMR; thiolysis; gallate; Rumex obtusifolius
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An acetone:water (7:3) extract obtained from the leaves of Rumex obtusifolius was fractionated into procyanidin oligomer and polymer fractions using a linear gradient and a simple step method on Sephadex LH-20. The chemical characteristics of the procyanidin fractions were studied by C-13-NMR spectroscopy, acid-catalysed degradation in the presence of benzyl mercaptan, matrix-assisted laser desorption/ionisation time-of-flight (MALDI-TOF) MS and electrospray ionisation (ESI) MS. The C-13-NMR showed that the polymer fraction consisted predominantly of procyanidin polymers, some with galloyl groups attached. The thiolysis reaction products indicated a mean degree of polymerisation (DP) of 4.3 for the step method, and a range of 2.3-8.2 mean DP for the gradient fractionation., with epicatechin as the most abundant flavan-3-ol extension unit, while the terminal units consisted of equal proportions of catechin, epicatechin and epicatechin gallate. Singly charged ions observed in MALDI-TOF/MS showed a range of oligomeric procyanidins and their polygalloyl derivatives. These species (in the range DP 2-7) were also observed by ESI/MS but the spectra were more complex due to overlapping multiply charged ions. Isolation of oligomers from the Sephadex LH-20 fraction by chromatography on polyamide and C-18 yielded B1, B2, B3 and B7 dimers, an A-type trimer and a B2 3,3'-O-digallate. Copyright (c) 2007 John Wiley & Sons, Ltd.
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