Salix daphnoides: A Screening for Oligomeric and Polymeric Proanthocyanidins

• Main Authors: Stefan Wiesneth, Frank Petereit, Guido Jürgenliemk
• Format: Article
• Language: English
• Published: MDPI AG 2015-07-01
• Series: Molecules
• Subjects: procyanidins; proanthocyanidins; flavan-3-ols; Salix daphnoides; willow bark; low temperature NMR; thiolysis; polarimetry; polymeric proanthocyanidins
• Online Access: http://www.mdpi.com/1420-3049/20/8/13764

In the present study, a qualitative analysis of proanthocyanidins (PAs) from an aqueous-methanolic extract of Salix daphnoides VILL. bark is described. Procyanidin B1 (1), B2 (2), B3 (3), B4 (4), C1 (5), epicatechin-(4β→8)-epicatechin-(4β→8)-catechin (6) and epicatechin-(4β→8)-epicatechin-(4β→8)-epicatechin-(4β→8)-catechin (7) have been isolated by a combination of different chromatographic separations on Sephadex® LH-20-, MCI®-, Diol-and RP-18-phases. Mass spectrometry, 1D- and 2D-NMR, circular dichroism and polarimetry were used for their structure elucidation and verification by comparison with the literature. Additionally, two fractions of very polar flavan-3-ols were compared: “regular” polymeric PAs received at the very end of the Sephadex® LH-20 chromatography showing no mobility on silica TLC and “unusual” PAs with the same RF-value but already eluting together with flavonoids in the Sephadex® LH-20 system. These “unusual” PAs were subsequently enriched by centrifugal partition chromatography (CPC). 13C-NMR, polarimetry, thiolysis, acid hydrolysis and phloroglucinol degradation were used to characterize both fractions. Differences in the composition of different flavan-3-ol units and the middle chain length were observed.