Phenolic compounds in the ethyl acetate fraction of a standardized willow bark extract

Recent pharmacological studies on willow bark extracts have shown that there is more than the effect of salicin and its derivatives alone [1]. Presumably, polyphenols like flavonoids contribute considerably to the analgetic and antirheumatic overall effect [2]. In order to investigate these flavonoids concerning absorption behaviour and pharmacology, a standardized willow bark extract (Steigerwald STW 33-I, extracting agent: water, drug:extract ratio 16–23:1 comprising total salicylalcohol derivatives 23–26% m/m) was fractionated and the polyphenol enriched ethyl acetate fraction used for isolation. All detectable flavanones and flavanonols were purified by open column chromatography, flash chromatography and RP-HPLC. Structure determination was carried out by mass spectrometry and NMR. Naringenin-7-glucoside, naringenin-5-glucoside, eriodictyol-7-glucoside, naringenin-5-O-(6″-trans-p-coumaroyl)-glucoside, dihydrokaempferol, taxifolin, naringenin, eriodictyol and the chalcones isosalipurposide and 6″-trans-p-coumaroyl-isosalipurposide were isolated, as well as catechol. Additionally, the phenolglucoside populoside B was identified for the first time in Salix sp. All compounds are under investigation concerning their anti-inflammatory activity in an ICAM-1 assay. The absorption behaviour of the flavonoids by using an in-vitro Caco-2 monolayer model and application of the whole extract in comparison to the flavonoid enriched fraction and the single compounds are under current investigation.

References: 1. Khayyal MT. et al. (2005) Arzneimittelforschung 55: 677–87.

2. Nahrstedt A. et al. (2007) Wien Med. Wochenschr. 157: 348–51.