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 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.
Spencer
Paul
P
Food and Health, AgResearch Ltd., Grasslands Research Centre, PB11008, Palmerston North, New Zealand.
Sivakumaran
Subathira
S
Fraser
Karl
K
Foo
L Yeap
LY
Lane
Geoffrey A
GA
Edwards
Patrick J B
PJ
Meagher
Lucy P
LP
D013058:Mass Spectrometry / Q000379:methods; D015394:Molecular Structure; D044945:Proanthocyanidins / Q000737:chemistry* / Q000302:isolation & purification*; D031804:Rumex / Q000737:chemistry*
D044945:Proanthocyanidins