Chromatographic Analysis of Simple Phenols in Some Species from the Genus Salix

Introduction - Salicis Cortex, made from willow bark is a herbal remedy, which is standardised based on the content of salicin, a compound with analgesic and antiphlogistic properties. However, clinical trials suggest that other compounds also present in Salicis Cortex can contribute to the pharmacological effects. Objective - To characterise the composition of phenolic acids in the barks of different species and clones from the genus Salix by use of chromatographic methods-HPTLC and HPLC. Methodology - The phenolic acid composition was analysed by MGD (multiple gradient development)-HPTLC technique. The separation was performed on HPTLC Diol plates with gradient elution using a mixture of chloroform:hexane:ethyl acetate with increasing concentration of ethyl acetate from 10 to 25%. Derivatisation with thymol reagent was employed for the first time for specific detection of phenolic acids containing methoxyl groups. Results - The presence of all phenolic acids previously reported in the genus Salix was confirmed, namely p-hydroxybenzoic, vanillic, cinnamic, p-coumaric, ferulic and caffeic acids. Furthermore, pyrocatechol as a constituent of willow bark was revealed. The highest concentration of this compound was observed in the S. purpurea bark (2.25 mg/g). Conclusion - The presence of a relatively high content of pyrocatechol in Salix species may raise doubts about the safe application of this herbal medicine. Copyright (C) 2010 John Wiley & Sons, Ltd.