Journal
PHYTOCHEMISTRY
Volume 65, Issue 10, Pages 1421-1428Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.phytochem.2004.05.003
Keywords
strawberry; Fragaria ananassa; rosacea; flavanol-anthocyanin; catechin-pelargonidin 3-glucoside; epicatechin-petargonidin 3-glucoside; afzelechin-pelargonidin 3-glucoside; epiafzelechin-pelargonidin 3-glucoside; rotamers; NOESY NMR exchange
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Flavanol-anthocyanin complexes were isolated by successive use of Amberlite XAD-7 chromatography, Sephadex LH-20 gel filtration and preparative HPLC from acidified, methanolic extract of strawberries (Fragaria ananassa Dutch.). These purple minor pigments were characterized by UV-Vis spectroscopy, 1D and 2D NMR techniques, and electrospray mass spectrometry to be catechin(4alpha --> 8)pelargonidin 3-O-p-glucopyranoside (1), epicatechin(4alpha --> 8)pelargonidin 3-O-beta-glueopyranoside (2), afzelechin(4alpha --> 8)pelargonidin 3-O-beta-glucopyranoside (3) and epiafzelechin(4alpha --> 8)pelargonidin 3-O-beta-glucopyrano side (4). The stereochemistry at the 3- and 4-positions of the flavan-3-ol units was based on assumption of R-configuration at C-2. Each of the four pigments occurred in the NMR solvent as a pair of rotamers. Proved by cross-peaks in the H-1-H-1 NOESY NMR spectra of 1, 2 and 4, the two conformations within each rotameric pair were in equilibrium with each other. Even though I and 2 are based on a different aglycone, their structures may be similar to tentatively identified pigments, which have been assumed to contribute to the colour of red wines. (C) 2004 Elsevier Ltd. All rights reserved.
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