Seasonal variation of lipophilic constituents in roots of Echinacea purpurea and E. pallida

Echinacea purpurea (L.) Moench and E. pallida (Nutt.) Nutt. are widely used for the unspecific enhancement of the immune system. The plants origin from North America and are grown all over the world as garden flowers or as medicinal plants. Lipophilic constituents such as alkamides and ketoalkenes/ketoalkynes are believed to be among the active metabolites in E. purpurea and E. pallida, respectively, with the highest concentrations being found in the roots. Most investigations on roots have been conducted on plants younger than one or two seasons and few have investigated the season variation of lipophilic constituents in roots of Echinacea species.

From early winter 2009 to fall 2010 five 4–5 year old E. pallida and seven 3–4 year old E. purpurea roots from the same population of plants were collected throughout one year (i.e. before and after soil freeze in winter, mid spring, at high soil temperature in the summer and mid fall). Lipophilic constituents were extracted from milled freeze dried roots with EtOH-H₂O (70:30) and analyzed by HPLC-PDA and LC-MS/MS.

The highest concentration of alkamides in E. purpurea roots was found when soil temperature was just above 0°C after winter and during summer, when the soil temperature was high. In the first case dodeca-2E,4Z-diene-8,10-diynoic acid isobutylamide was the major alkamide and in the latter case dodeca-2E,4E,8Z,10E/Z-tetraenoic acid isobutylamides were the major constituents. For E. pallida roots the highest concentration of 2-ketoalkenes and -alkynes were found when the soil temperature was just above 0°C after winter and here the major constituent was pentadeca-8Z,13Z-dien-11-yn-2-one.