Introduction
Germacrenes A–C are secondary metabolites produced by various plants. They are sesquiterpene hydrocarbons bearing the (E,E)‐1,5‐cyclodecadiene structure known to undergo thermal rearrangement through a [3.3]‐sigmatropic reaction. Such a rearrangement was evidenced by comparing the contents of a given germacrene and the corresponding elemene calculated by GC‐flame ionisation detection (FID) with the relative intensities of the signals of both molecules in the 13C‐NMR spectrum of the mixture, recorded at room temperature.
Objective
To develop a protocol to identify and quantify germacrenes A, B and C and in parallel the corresponding elemenes, using a combination of GC‐FID and 13C‐NMR and then provide a correct analysis of Cleistopholis patens essential oils.
Methods
The essential oil was submitted to GC‐FID, GC‐retention index, GC–MS and 13C‐NMR analyses. The relative percentages of every couple of germacrene and elemene measured by GC‐FID were summed. Then, the relative ratio of the mean intensities of the signals of the protonated carbons of a given germacrene and the corresponding elemene was calculated. The contents of both compounds were obtained by combining GC‐FID and 13C‐NMR data.
Results
The true content of germacrene A/β‐elemene, germacrene B/γ‐elemene and germacrene C/δ‐elemene in leaf and root oils from C. patens was evaluated by combination of GC‐FID and 13C‐NMR data. Correct analysis of the essential oils was provided.
Conclusion
Combined analysis of essential oil including 13C‐NMR without isolation of the components, appeared really efficient to identify and quantify germacrene isomers and in parallel elemene isomers in essential oils. Copyright © 2013 John Wiley & Sons, Ltd.