Analysis of the constituents of aqueous preparations of Stachys recta by HPLC-DAD and HPLC-ESI-MS

Herbal teas are one of the most common forms of oral aqueous preparations, used also externally in traditional medicine. They are obtained from one or more herbal substances by means of decoction, infusion or maceration [1]. In continuing our studies on traditional preparations of herbal drugs [2,3] we report the investigation of infusions and decoctions of Stachys recta L. (yellow woundwort). A method based on HPLC/DAD coupled to an ESI interface was developed for the determination of phenolic constituents in three aqueous preparations of S. recta. The assay was simple, effective and permitted the quality control of S. recta decoctions and infusion. The method was validated for the linearity, repeatability of the standards and samples, time precision, limits of detection and quantification. Overall, 30 constituents were detected and identified, belonging mainly to three classes of compounds: caffeoylquinic acids, phenylethanol glycosides and flavonoids. 15 of them were quantified having a lower limit not less than 0.02% of the lyophilised extracts. Only 7 of them were previously reported in this species, while 23 were identified for the first time as constituents of S. recta. HPLC-DAD-ESI-MS analysis provided evidence for the certain identification of the main constituents and in some cases of their isomers. Eight constituents were isolated and their structure elucidated by HPLC-ESI-MS and 1D- and 2D-NMR spectroscopy. Among the investigated preparations, the infusion is the best method to extract the native costituents of the plant, while decoction is a more aggressive treatment and causes partial degradation of some acylated flavonoids.

References: 1. European Pharmacopoeia 6th edn, Vol. 1, Council of Europe, Strasbourg, 2008. p.685.

2. Bilia, AR et al. (2007)J. Pharm. Biom. Anal. 44: 70–78.

3. Bilia, AR et al. (2002) Drug Dev. Ind. Pharm. 25: 611–22.