Isolation and Characterisation of Procyanidins from Rumex obtusifolius

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 13C-NMR spectro...

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Bibliographic Details
Published in:Phytochemical analysis 2007-05, Vol.18 (3), p.193-203
Main Authors: Spencer, P, Sivakumaran, S, Fraser, K, Foo, L.Y, Lane, G.A, Edwards, P.J.B, Meagher, L.P
Format: Article
Language:English
Subjects:
13C-NMR
chemical structure
ESI/MS
gallate
MALDI-TOF/MS
Mass Spectrometry - methods
Molecular Structure
Proanthocyanidins - chemistry
Proanthocyanidins - isolation & purification
procyanidins
Rumex - chemistry
Rumex obtusifolius
spectral analysis
thiolysis
weeds
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Summary: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 13C-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 13C-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 C18 yielded B1, B2, B3 and B7 dimers, an A-type trimer and a B2 3,3-O-digallate.
ISSN:0958-0344
1099-1565
DOI:10.1002/pca.967