Three tetraene alkamide isomers were identified in Echinacea angustifolia DC. and Echinacea purpurea (L.) Moench roots by comparison with their synthetic cis-trans 8,10 counterparts which were synthesised using novel pathways. The three tetraenes were:
(2E, 4E, 8Z, 10Z)-isobutyldodeca-2, 4, 8, 10-tetraenamide, the ZZ isomer,
(2E, 4E, 8Z, 10E)-isobutyldodeca-2, 4, 8, 10-tetraenamide, the ZE isomer,
and (2E, 4E, 8E, 10Z)-isobutyldodeca-2, 4, 8, 10-tetraenamide, the EZ isomer.
The EZ isomer has not been previously reported to be present in Echinacea species.
The relative concentration of each tetraene was examined in several commercially available samples by GCMS. The amount of each tetraene as a percentage of the total differed between the two species, with 10% and 29% of the ZZ isomer, 80% and 63%of the ZE isomer and 10% and 8% of the EZ isomer in Echinacea angustifolia and Echinacea purpurea respectively. These species differences between Echinacea angustifolia and Echinacea purpurea roots may help to explain experimental differences in the activity of preparations from either species as well as the variations in their efficacy noted in clinical trials.
